Devin Devine, contractor based out of Blakeslee Pennsylvania, projects competed across the USA
contact devin@devineescapes.com serious inquiries only
This DIY article; and the rest of the how-to section of my blog, cover much of the basics of how-to properly build flagstone patios. If you need guidance for site-specific issues for your stone hardscape installation I offer consultation services as well.
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Flagstone: what to use, sand, cement, or gravel?
So getting right to it then, what type of foundation are we going to build for our flagstone patio: sand, cement, or gravel?
Short answer: well it depends. Quarry screenings are generally best for under the flagstones. Screenings are also one of the best options for in between the stones. However, there are other options available which can be utilized to achieve different aesthetic effects. First we will address the structural issue “what to use beneath the flagstone”.
Cement—it will (probably) crack, at some point. May last for quite awhile, but when it does fail it will be much more work to repair it then to repair dry flagstone work.
Sand—ants will dig it up and get it all over the place…also the sand may wash away, causing stones to settle.
Gravel—really no problems here, just use the right type of gravel. Better yet, use road base gravel for the foundation and then use stone dust aka quarry screenings aka grit aka quarry dust as the final leveling agent.
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Short video showing how to level a dry set flagstione, wobble free.
flagstone patio with branching mosaic, stone art….in old San Francisco! (yes, I travel for work)
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Why is gravel the best choice for your your flagstone patio’s foundation?
Cement will (probably) crack. Especially grade level cement. Especially in a climate with winters like ours in Pennsylvania. A worse way to go about it would be to lay the flagstone upon a bed of gravel and then cement the joints between stones. Horrible idea. The gravel base is flexible and will move ever so slightly during freeze-thaw. Well, if the base was done poorly the movement might be more then slight, but let’s assume the base was done well. A gravel base will definitely move a bit—looking at any of my patios, you’d never know that, but the movement does happen. Cement is rigid—if you put a rigid top on a flexible base then systemic cracking is inevitable.
Cement based mortar is a fine joint filling material if the flagstone happens to rest upon a concrete foundation. But why on earth would you want to have a concrete foundation anyway? The concrete itself will crack, eventually. In a northern climate it will likely crack within ten years—and the chances of it cracking within the next three years are pretty high too. Environmental impact of concrete production is no small issue either. Anyway, I personally prefer dry stone work. More harmonious, warmer, just better. The feeling you get from a well done dry laid flagstone patio, in my humble opinion, is just better than a flagstone patio set in cement.
Related Content: what about paver base panels?
A flagstone patio set in cement can of course look good and last a long time. I’ve built many that look great,–many years later too. But if there is cement between the joints, there just had better be a concrete foundation. I mean it.
Tools needed to build your stone patio on a gravel base:
- GRABO, the hot new vacuum lifter that makes lifting flagstones a bit easier. My review can be found HERE. Do you need one? No, but on a larger patio it will save time and save you some strain on your fingers. Bigger than 200 square foot–maybe get one. Bigger than 400 square foot–yea, probably get two.
- dead blow type mallet. Many types to choose from….lately I mostly use my rawhide mallet, but the rubber headed modern style deadblow is in my tool bucket too, and I’ll use whichever is closer on hand.
- brick hammer, for cutting flagstone.
- Angle grinder. Same one I use. Keep this on hand for cuts that the hammer won’t successfully make, or that will take too long with the hammer
- Diamond blades.
- Brick chisel.
- A couple of 5 gallon buckets (for stone dust, when leveling stones)…shovel, wheel barrow…..4′ level.
- Pick maddock. Best way to dig. Break up soil with this, then use shovel.
- Knee pads–essential.
- Hand tamper and/or plate compactor. For 100 square foot or less, I’d just use the hand tamper. Bigger than that–you might want to rent plate compactor.
stone dust is the answer
Sand….well, if you use a really heavy course sand then you might get away with it. For awhile anyway. Most of the sands that are packaged for sale however are way too fine. You can use a course sand for under the flagstones, sure. Back when I used to lay brick patios I would use course sand or quarry screenings inter-changeably and it was fine. Them patios still look good. Those are brick patios however, where the space between the paving units is about a quarter inch wide. The problem with sand is that it washes away by action of water, blows away by action of wind, and gets carried away by action of ants. That’s why stone dust AKA screenings AKA decomposed granite works much better, for underneath flagstones, than sand.
Learn how-to use the stone dust as a leveling agent: the process is described HERE.
New! dry set mosaic path
Not as good as my flagstone patios though! Problem with using even course sand beneath flagstone is this: Bricks are of uniform thickness. Thus it’s not too much trouble to just get your gravel foundation pretty close to perfect, then go ahead and screed out one inch of sand for your bricks to rest upon. With flagstone however, the thickness will vary too greatly—you may need half an inch of sand for one stone, but 2 inches for another. If you are using sand, then that variation in thickness will cause problems. Screenings are almost the same thing as modified gravel—they are indeed one of the two ingredients in modified gravel…they are heavy enough that it really is no problem to use 2 inches on one stone and half an inch on another—ten years down the road, that patio will still look sharp.
flagstone patios that are set in sand are vulnerable to ants and wash-out
Occasionally I’ve seen a paver patio messed up by ants. But with flagstone patios that are set in sand ants always attack. I suppose it’s because the joints are inevitably wider with flagstone and/or because the flagstones are varying in thickness meaning you end up with deeper sand in some places. Whatever the exact reason, I can tell you that all of the flagstone patios that I have seen that are set in sand eventually get run amok by ants.
Another reason to use screenings is because screenings also make an excellent joint filler.
You do not want to use sand, even course sand between your flagstone joints because it can wash away—unless of course your flagstones are absurdly tight. For pattern-cut flagstone, yes, you can maybe get away with using sand as the joint-filler. Just make sure the base is course sand, not fine. You will need to use fine sand for the joints however because of how tight they are. Again, ants love fine sand—but in this application, pattern-cut stones, tiny joints—fine sand will not be the end of the world—so long as the base is course, of course. That’s for pattern-cut flagstone–or any flagstone where the joints are super tight–in those cases you can maybe get away with sand, so long as you follow the guidelines that I’ve set earlier in this paragraph. For irregular flagstone, or any flagstone with a joint wider than a quarter of an inch, you really really should try and avoid sand, and instead use stone dust.
Can you set flagstones down on your own native soil?
Your own native soil –This one would be great, if your own native subsoil consists of about 20-40 percent clay and the rest mostly sand and gravel. And hadn’t been disturbed in ten years. Then you’d have a good solid base already 🙂 You could most certainly take clay from your subsoil, figure out how much sand and gravel it already contains, and then calculate how much gravel ought to be added, and then fetch some gravel from elsewhere nearby.
What I am talking about here is using the onsite materials, to attempt to mimic the performance characteristics of road base and/or to create a gravel cob-like mixture of soils, well draining, compactable and stable. This type of work is still in the r&d phase for me. More on this, as the research progresses. Suffice it to say that yes, it can be done, but it’s a bit complicated and beyond the scope of this present article.
Okay, so let’s stick with gravel for the foundation, and screenings AKA stone dust as the leveling agent
Back to screenings—when you use screenings for both the leveler and the joint filler for in-between your flagstones you are creating a good scene. If there is ever any minor issue with the screenings underneath the stone it shouldn’t matter too much because the joint filler will settle down and fill the void beneath the flagstone. Having screenings up top and down below, it just works out well.
You can expect to top off the screenings once within the first year—a small bit will settle or wash away. No problem, just sweep in some new material and you’re good. After that, in future years, you’ll be fine. My best recommendation is that clients hire me to do maybe a couple hours maintenance once a year—by no means is this necessary, but I like my work to sparkle.
And it does. Check out what my past clients have to say about my work.
One thing I have not gotten into in this article is polymeric sand. I point you now to another hardscape how-to blog post, if you are curious about poly-sand. If you are poly-curious, that is.
I don’t know what you do with your leftover flagstone, but here’s what I do with mine:
Stacked stone spheres and garden sculptures, by Devin Devine.
I should maybe also add that using the above system I have never once had a single flagstone patio fail. Okay, maybe one stone with some minor settling—fixable in a few minutes (and rare, very rare that ever happens) but never any major problems. Been doing this a little while too(since 1997). On my largest flagstone patios I generally would recommend 3 hours of maintenance work should be done, every few years or so. This will keep the patio in optimal shape. I’m picky and want my work to look perfect forever. Often I’ll return to a client’s house years and years later and it will still be in perfect shape. Without any maintenance needed!
Related content:
- leveling flagstone in stone dust, a detailed how-to
- DIY phone or email consultation services
- Do not overfill your joints: read this post
- Learn how-to use a hammer to cut and fit your stones nicely: check out THIS article.
- how to build a stone bird bath
Patio I built in Northern California circa 2018. If a project interests me I can be convinced to travel for.
Looking for Expert Advice from a flagstone professional? Phone Consultations now available!
If you still have questions and would like some help, that’s okay because I now offer consultation services. Shorter questions and comments are most welcome in the comment section below. Donations are appreciated.
Thank You
Hi Devin! So excited I found your blog! My fiancé are DIYers hoping to cover an existing concrete slab (10 years old with no cracks we live in Houston, Texas–no freezes) with flagstone and have been researching the best way to go about it. We were told by the guys at the stone yard to adhere with mortar and fill joints with either mortar or polysand but I’m concerned about cracks and even more issues now that I’ve read your other posts. I’ve also read about using a poly construction adhesive to adhere pavers around the circumference of the patio and then lay sand for the flagstone in the middle of the pavers. This is supposed to keep the sand from washing away and maintain the border of the patio but I hate for the sand to be coming out of the joints all the time and making a mess on the patio. I looked around to see if there’s any stone dust/grit here in Houston but can’t seem to locate any. What do you think? Is there another option you would recommend?
Using construction adhesive to adhere pavers along the outer edge of a concrete slab–this a common enough practice, and one which I used to do myself, back in my paver laying days. It’s entirely applicable–if you are using concrete pavers, or similar, small sized paving unit. As you described, you just glue the outer ones, inner pavers are contained thusly.
For flagstone, I personally just set larger stones on the edge–stones to big to wobble or come loose. Sight-unseen, I can really only provide general guidelines. I do not know what your stone looks like, how thick, how much surface area…..what your local sands and other soils are like…..which quarries sell stone dust/grit/screenings…..
One good piece of general advice–use what you have close at hand. In my area, screenings are the local material with the best physical properties for the task at hand: leveling out flagstones and filling in their joints. But then, I could use local clay soil as the leveling agent–I’d make sure no organic material got in there. i could use sand….and simply deal with the fact that ants often love it.
So yeah, that’s probably what I’d do in your case: set larger stones on the edge of the patio. Use the best local soil/sand/grit for leveling that you can find. a heavier duty sand, with larger, chunky bits would probably be best. I hope this helps–and let me know how it turns out, and good-luck!
Thank you so much Devin! We’ll see what happens and keep you posted! 🙂
Devin, I enjoyed reading your articles. Thanks for all the informative advice. Do you have articles that discuss sealer on flagstone patio and flagstone path? Thanks.
Nope. I’m not into sealing flagstone though. First of all, it usually becomes slippery. Second of all it’s just not needed. I’ve occassionally used it on repair jobs, when repairing cemented in flagstone. That’s about the only time I’d consider sealing flagstone–in a wet-laid job where I was repairing a patio/walkway that’s over a decade old. After re-pointing the flagstone and re-setting any stones that are loose, I’d maybe worry about the mortar that’s underneath the flagstones that I did not need to re-lay. That old mortar–is it compromised by water getting down there? If I think it may be, then yeah, I might recommend sealing the flagstone as an added insurance measure….not needed at all for dry laid flagstone. And I whole-heartedly recommended going with dry stone–unless your doing a repair of course. Good luck!
Hi! We are in Southern California and Our landscaper put DG (and sealed) between our flagstones with wide gaps. It’s always a mess and my kids may have gotten too much water on it. Now a portion of it has turned darker and is sort of muddy and it’s been that way for a week or more. I really don’t want this filler anymore and would prefer something more stable and solid but i keep seeing mixed information. A cement mixture sounds good because of its stability and no mess, but do you have a better suggestion??
I sure do. What you want is a DG joint–but not too wide and not over-filled. I never recommend a sealer, or cement/mortar, for a flagstone joint because the gravel foundation is flexible–put a rigid joint there, a sealed joint there and the joint will crack. Even a plastic joint that can bend a bit, will crack. The other problem with a sealed joint is that voids will form underneath a flagstone. Using DG as the joint material, the DG will settle down into those voids. Now imagine that DG is sealed and the top inch or so stays put….now there’s voids beneath the joint. Joint will fail because of this, someone steps on the hollow joint and it breaks up. A cement joint will have the same sort of problems. With a DG joint…it just settles down, and only needs to have some new DG swept into place. Takes a couple minutes.
Have the flagstone well-fit, with an inch wide gap between the stones (half of the reason why polymeric sand and joint stabilizers are popular is because people think they can use such a product and it will allow them to get away with poorly-fit, wide gapped flagstones. It will not.). Fill this even, 1″ gap with DG, hose down, sweep off, then top off again and hose down, sweeping off excess–and leave the joint about 1/4″ recessed. Follow this procedure, and you’ll be in good shape.
I’ve used this method in California and also in many northern areas, with heavy rains in the spring/fall and hard frost in the winter.
Hello Devin, Your info is great on here but I have a unique situation. About 15 yrs ago, we put a paver and brick patio over a flagstone patio. The flagstone was a mess and the patio was too low. They filled the joints with what I think they said was portland cement and coarse sand that had shell bits in it. I am not sure about that but I need to repair some sections. I have no idea what to use. I don’t want to take all of it out because it is too costly. I am in South FL and I was thinking of stone dust but will that hold with the base of another patio? I researched the polymetric sand that was non staining but it doesn’t sound great either. I am at a total loss. The fill was a light gray color that has lightened over the years. I liked that it had texture to it. Any suggestions would be greatly appreciated.
There’s too much here that I don’t know. The short answer will probably end up being stone dust… But without seeing photos I can’t be confident with that answer. I’m reluctant to say even that though, because with incomplete data, I don’t want to give you an incomplete assessment. If you want to set up a phone consultation, then email me photos, before and after if possible. My answer will likely be clean out the old joint material and replace with stone dust. Since this is a paver patio though…. I might recommend play sand/fine sand.
If the old joints are cement based, then you may likely need an angle grinder and/or chisel to remove the old material.
Hi devin im in SW florida and i punched out a walkway entrance thats basically 4’ x 9’ ( i swirled it a little so its more interesting i have natural flagstones how much base of gravel should i use and then how much screening on top of that
In Florida, 4 inches of road base will be plenty. Lay out your flagstones on top of your foundation and then level each stone individual in 0-1.5″ of stone dust/screenings as needed, in order to level it up.
More info
And a bit more
regarding post about DG. What is DG?
Decomposed Granite.
Devin,
I have a question regarding the base material & screed layer for a dry laid bluestone patio in north western NJ. The bluestone is a 2 inch uniform thickness with variable shapes. Here in this area, crushed stone road base is called QP (quarry process) which consists of 3/4 inch crushed stone with fines. Can 3/4 inch clean crushed drainage stone (no fines) be used as the base layer with a 1 inch layer of clean crushed 1/4 inch stone as the screed/leveling layer? The joints will be stone dust (1/8 inch & fines) as you recommended. Since this proposed base & screed layer are “porous” (clean stone), the joint filler material may be more prone to settle?
Your thought?
If your foundation and your bedding material are both clean stone, free draining–then fine joint material will just settle and sink.
I see no reason to use clean stone as the foundation or for the leveling agent. Fines–are compactable.
If I was to use clean gravel for foundation and 1/4″ clean for the bedding—then I’d use the same 1/4″ clean for the joint.
Be warned, such 1/4″ clean gravel may get all over the stone surface and be a bit of a mess. So if you do use it–then leave your joints well recessed. I leave them recessed when using fines–but with no fines, I’d leave them a good half inch recessed.
Also, the clean joint material doesn’t lock in well like the fines –so each stone should be large enough that it doesn’t wobble underfoot. Use larger stones, certainly nothing less than a square foot, but maybe nothing smaller than 2 square feet.
Meanwhile……I’ve been working in PA, NY and NJ for decades, using fines. No problems have been found……I check in on my patios 10 years later–and they look great.
https://www.devineescapes.com/wp-content/uploads/2024/05/Screenshot-2024-05-28-at-14-53-58-devine-escapes-Google-Search.png
Decomposed granite for leveler, and joints. As far as the border goes, you can just glue your pavers down with liquid nails. You’ll do fine!
Good point. Stefanie had indicated that she looked and couldn’t find stone dust or grit in her area. Of course the same product is also called decomposed granite, 1/8 inch minus, 1/4 inch minus or screenings, quarry dust…. Stone dust has many names and is available just about anywhere in the us.
Then again, her question was asked about 4 years ago 🙂
OMGoodness! Devine has saved me from the same fate! Had I not stalled and found Devine’s articles, I would have gone with the recommend road base and sand under my flagstone and then filled with polymeric sand.
The road base turned out to be only ONE inch and the sand was 2-3 inches. Nightmare. I’ve since dropped continuing the project and having to do it myself. That is, after I had them take out the sand–but of course, there is still much sand remaining. I am trying to do this myself. I would hire Devine is a second if he were several states closer. I’m in CA! Devine you have been a godsend!
Yea, 1 inch of road base and 3 inches of sand doesn’t sound sufficient–even in CA where you don’t have the harsh winters.
I do travel for work, and have done jobs in CA, but with the current covid situation I probably won’t be out west again until maybe winter/spring. So IDK, but if your project still isn’t finished in December/January…then maybe?
Sounds like you’re going DIY though, so you might want to check out this article too:
Cut flagstone hammer
Glad I could help!
I am also in So California (no ground freeze here) and i am about to install 1-1/2 Oklahoma blue flagstone (2 ft x 3 ft pieces) and i live on clay soil.
Can you please suggest a recipe for the gravel thickness and the DG thickness ?
An emphasis on reducing the amount of gravel (unless foolish) would be great so that there is less soil to remove
The industry standard for dry laid flagstone foundations in California is 3″ road base gravel. When I’ve worked in California we always did 4″-5″. Local guys said that was overkill….but the local guys who are serious about stone agreed that 4″ is better.
Do the foundation, lay out the puzzle, then level up each stone one at a time, using pathway fines or dg as your leveling agent.
More info
What does DG mean? I had large flat stones put in my yard and the guy put pea gravel between the stones weeds grew up between them . He now wanted to put a sealer over them to make them stay put. Should I or not. We have a granite place not far from us where it comes out of the ground. I saw a show on tv where they used the same thing but sprinkled a powder in the pebbles that when moist gets on it it will make they stick together. Any idea what it is?
Decomposed Granite is crushed stone, in small size and with fines. More info on this material. Use this to level your flagstones and as a joint material. Pea gravel is no good, no adding of binders will correct the situation. There certainly are tv shows where they tell you how to pour plastic in between pebbles, to keep them in place–these are bad shows, giving bad advice. Fact is, if you are using stone in your landscape then there is no need to also use plastic. You don’t need fabric, you don’t need plastic edging, and you certainly don’t need any liquid or powder plastic binders.
Stone dust/DG/pathway fines is crushed stone, than contains stone flour–fine, flour-like particles that semi stick together, when damped and dried. The plastic versions cost more, are toxic, and do not work as well (will crack up, and take more work to repair).
Your system of using stone dust for the joint filler is the best method, is there any way to get a different color established with using it to match different shaded flagstone.thank you
You mean a way to get the stone dust to a particular color–in order to get it to match the tone of your flagstone? Sorry, I’m not perfectly clear on your meaning…
Most gravel quarries produce screenings, different quarries will have different colored stone.
I have mixed red stone dust a dark grey stone dust before, to get a more purple looking joint.
In South eastern Pennsylvania, where I do most of my work, I can readily get off-white/cream colored stone dust, grey/blue, dark grey/black and red screenings.
Good luck!
Hi Devin, I’m in southeastern PA and hoping to DIY a flagstone patio. I’m having trouble sourcing stone dust. Anywhere local you recommend? Thanks!
Any masonry supply/hardscape supply will sell quarter inch minus stone dust, the local name for it being “screenings”. Buy it by the yard.
I have a field stone walkway on a slope that is laid on a base of stone dust and using stone dust between joints. Problem I have is that the stone dust between joints washes out after a rain and I have to add more stone dust several times a year. I want to use polymetric sand to seal the joints and make them more waterproof. Do you recommend?
I do not recommend using polymeric sand with flagstone.
https://www.devineescapes.com/polymeric-sand-is-often-recommended-for-filling-in-the-joints-between-patio-stones-i-do-not-recommend-this-practice-and-i-will-tell-you-why/
A) the joints may be too wide. I prefer to keep my flagstone joints pink-width. Thumb-width is good too.
B) the walkway may be pitched to hard.
You want your walkway pitched to shed water, about 1/4″ pitch per foot. So, if you’re checking a four foot long atea of flagatone, then it should be off-level by about 1 inch.
C) if all the above is correct then maybe what you’re looking at is not a problem. It’s maintenance.
https://www.devineescapes.com/how-to-clean-dry-laid-flagstone/
I tell my customers that usually we can expect that a flagstone patio or walkway could use a joint top up once or twice a year.
If the joints are pinky-width…then it shouldn’t be much of a problem, if a joint or two is a bit low. You want your joints recessed a bit anyway.
In my experience, the joints often need less and less topping off as the years go by. The stone dusts settles over the years, locks in tighter. Ambient dust gets in there and helps bind it up a bit. Moss may up residence.
Shouldn’t be a problem. Should be 20 minutes of sweeping and hosing per year….polymeric sand (more often then not) will fail miserably within 3 years.
What about using item four for a base
Yes, whenever I do jobs in New York this is what I buy. Item 4 (in New York) is 3/4″ crushed stone with fines aka 3/4″ minus, aka road base gravel.
Hi Devin,
Thank you for this post about using rock screenings to fill the gaps. We had a flagstone patio professionally done for us this past summer. After seeing the quality and artistry of your work, I’ve realized that our contractor was a novice. He used the local roadbase – gravel and soil to level the grade and lay the flagstone, and then went over it with a compactor. The problem is that we have mud, dust, and loose gravel everywhere. Some of the gaps between stone are more than an inch wide. How would you approach filling the gaps with screenings. A sweeping and topping off? Or some other method? Thank you for your expertise.
Tessa,
Sorry to hear your difficulties. I just take a shop broom and brush the screenings across the flagstones, back and forth until the gaps between the stones are filled to the top. Do this for the whole patio, Gathering the extra screenings into a pile then into a bucket and out of the way. Then soak the whole patio with a hose on shower setting or similar…..let it dry off a bit, then get out the broom again, because some of the joints will have settled, so you’re going to want to repeat the process.
Takes some time and patience, a bit of back and forth, but it’s a pretty simple task.
Good luck!
I just had 2 areas of my patio done professionally in flag stone
He used sand as a base, the joints were filled with pea rock.The problem is that the pea rock is coming out of the joints.is there something we can do to keep them in place?
My advice is to remove the pea gravel. Terrible choice for flagstone joints.
Now I’m happy to advise further, but first I would really need to see a photo of the patio and know where you are located/what type of winter your region experiences.
How wide are the joints, is it pattern-cut flagstone or irregular flagstone and is your region warm enough that sand is actually a proper foundation? All these questions are more can be solved with a photo and a location. Thanks.
If the joints are tight, stone dust might be the way to go. If they are wide and/or irregular, than soil and grass might work. Or moss, clover, irish moss, or some other ground cover. But pea gravel. Pshhh, nope. And on sand? Not in my hardiness zone.
When I call around in my area and ask if they have stone dust or screenings, they say they have 8910. Is that the same thing? They also mention manufactured sand (apparently very fine limestone). I have 8910 as my base and am looking for something for my joints.
Thanks
You must be from the South. Yes, same thing. 8910 is stone dust, dines, screenings–same stuff.
Thanks so much
At what width of joint will the stone dust not work well? Any?
You’ll want to try and keep your flagstones fit pretty tight together. You get much wider than 2 inches or so, and you tend to get into problems. This doesn’t mean that you need to measure every joint–with irregular stone, the joints are not going to be uniform–but when I see flagstones that are set half an inch to 2 inches apart, there tends to be no problem–you get into 3 inches plus, and the stone dust tends to get kicked out, by foot traffic, wind and rain.
Hi Devin,
We are located outside of Denver, CO with clay soil. We have a DIY project to set good-sized irregular flagstone in a wide-set single row, 1-2 fist width apart, as a meandering path in front of the porch, in place of the river rock that currently fills the area (20 years).
We thought to remove the river rock where we want to set the flagstone and leave the rest (around the flagstones).
Should we set anything under the flagstone or just level it, with a grade for water runoff? Thanks so much.
For a stepping stone path, I dig down, tamp, set 3 inches or so of gravel, tamp, and then set the flagstones on that, at the proper height.
Hi Devin, great information! What size gravel do you recommend to use underneath the flagstone as foundation?
3/4″ minus. The name, and the exact consistency will vary depending on where you are located, but generally speaking you’re looking for 3/4″ or 1″ gravel with smaller bits of stone mixed in, all the wall down to stone dust or stone flour. Some places will call it crusher run, or paver base….in New Jersey we’ve seen it sold as crushed stone #411, in Pennsylvania it’s called 2a modified, in Ohio they sell it as #304 stone, California calls it road base.
Hi Devin, I am planning a new 16’ x16’ flagstone patio in Ontario. The foundation will be crushed stone and screenings. The flagstones are 1” thick straight cut. My challenge is I am going over two 28” diameter septic tank covers ( the tank is 4” wall concrete – installed 5 years ago). To create a foundation to span the covers I was going to build a 29” square wood frame around the covers from 2×8” wood. On top I would put 3/4” pressure treated plywood then 1/2” concrete board then a layer of schluter ditra membrane. On top of that would go a 30” square piece of flagstone. Any thought on my solution?
I’d put the membrane between concrete board and wood–not between concrete board and stone. If using membrane at all.
Okay–so I just looked up the barrier you’re talking about using. I don’t see why it’s necessary here, and I don’t see just why you’d need both the barrier and the concrete board. Fact is, you could probably get away with gluing directly to the pt lumber. But lumber can shrink and swell, even pt lumber, over years. So I’d attach cement board/hardy backer to the wooden frame via exterior screws (and glue) and then glue the stone to the cement board, using this sort of adhesive.
Also, I’d consider building the frame from smaller lumber, like 2 x 4″ or something. I’d adhere the flagstone to the concrete board using pl loctite premium construction adhesive–or similar
Have you dealt with gophers? Can you recommend best patio choice and method of installation for unstable land and gophers?
Thank you!
Gophers aren’t so much of an issue on the east coast and most places I’ve worked at. But I do communicate with people across the usa and have heard of using chicken wire as an underlayment and as a perimeter. Like an underground fence. I’d look for a wire mesh of some sort with openings too small for a gopher. Of course peppermint oil, hot sauce, loose tobacco and etc are all things that will help keep the gophers away. Maybe use the peppermint for a month or so to get them away from the area–then build, using the wire underlayment. I also might* consider going deeper with my foundations, possibly using larger aggregate than usual, and maybe a layer or 2 or fabric–to both stabilize the soil and make it less attractive to gophers.
Hi again Devin, I’m from Santa Cruz Ca and planning a front yard flagstone path and patio. I like your recommendations of using screenings over base rock with the screenings also used in the joints. Couple other questions if you don’t mind, what do you use an an edge to the flagstone? I hate plastic bender board but a lot of the pros use it. I’m thinking of using larger 4-8 inch river rock. Will that work to retain the path and patio? Any suggestions? Also, would you use a weed cloth in between the gravel and the leveling screenings?
thanks!
Chris
Plastic edging should not be needed in a flagstone path. it looks tacky and is just unnecessary.
Weed cloth is used underneath flagstone, usually not to prevent weeds (it does NOT prevent weeds anyway) but to stabilize the soil in places that have a freeze thaw, like in Pennsylvania–not santa cruz. It’s generally laid beneath the gravel, between the subsoil and gravel layers. if you try and lay it between the gravel and the screenings you may have frustrations when it comes time to level out each flagstone.
Plastic edging…nope. I address this issue here:
https://www.devineescapes.com/ask-devin-plastic-edging-for-flagstone/
In short; just use larger and thicker stones at the edge of your patio or walkway. Any stone at the edge ought to be at least one square foot in surface area. Smaller stones can be used in the center of the patio or walkway, but larger ones for the borders. A river rock edge could also be used. You can also use smaller pieces of flagstone, laid on edge like a a curb stone and buried over halfway into the ground, as an edging. But again, use big enough stones on the border, and no edging will be required. Follow the above link for more detail on this issue.
Properly laid flagstone does not need any edging. It takes a bit of skill….for a “pro” it should be no problem. But then, some “pros” uses plastic edging, so real pros may be hard to find.
Attention universe: I would like to travel. There seems to be a lack of flagstone pros in this world. Give me a place to stay for the duration of the project and I can travel to your location–might not cost as much as you think.
Anyway, I hope my advice has been helpful 🙂
enjoyed reading your posts, getting educated about hardscape… would you like to spend a few days in Virginia beach? warmer than pa, and we have a diy project now that the concrete guys took my 50% deposit and never came back!!
Oh–sorry to hear that. I do travel for work, and I do offer professional assistance for DIY hardscape projects, so me paying you a visit is possible. Send me an email or give me a call during the daytime then, let’s talk.
Thanks for sharing all of your expertise, Devine. I completely forgot to use the weed barrier on my project. I’ve already laid my stones. Will this present a major problem?
It shouldn’t. I sometimes use filter fabric between the soil and gravel–this does nothing at all to prevent weeds, and is considered unnecessary and inessential. The filter fabric can possibly help minimize future maintenance and can help to stabilize soils which are prone to movement or excessive dampness. You can build a stone walkway or patio without fabric…I do, nine out of ten times (at least) there’s no fabric beneath my jobs.
Thank you, this answered my question about using weed barrier. I’m pulling up flagstone from original owners design and it is full of weeds and I’m just hoping the method of weed barrier, gravel, decomposed granite/quarry dust will do the job for my patio that will serve as our firepit area. BTW, I’m in IL so we definitely get all seasons up here.
I am a DIY retiree building my 1st patio with a fire pit.
It is 17’ in diameter with a 40” diameter x 12” deep pit.
I’ve removed 8” of top soil and fill in 6” (3; 2”lifts packed).
My issue is I’m wanting to use a brown sandstone rock that averages 5” thick and weigh 40-60lbs each. I have 1/2 of the rocks laid out in a pattern and am leveling them up now.
Should I stay with the decomposed granite in between the uneven adjoining sides or are you suggesting something different and I was thinking 2” separation or do you recommend a tighter connection?
Thanks
That’s rather thick stone. May be more of a cobble than a flagstone even. But, either way, I use 1/4″ minus or decomposed granite, both as the leveling agent and as the joint material. As far as how close they need to be, I wouldn’t go any wider than 2″. Maybe inch/inch and a half. Often, if you set the stones and inch apart, they end up looking 2″ apart–because the sides are not a 90 degree angle in relation to the top–the tops being somewhat rounded off. My method is described here.
Hi Devin, do you recommend using weed cloth between the stone dust and base rock? If no weed cloth will the stone dust filter down into the base rock layer over time? My base rock is pretty well compacted so I’m trying to not use any landscape cloth if I can avoid it.
thanks,
Chris
What do you mean by base rock? If your base rock is well compacted, and is comprised of gravel mixed with stone dust/2a gravel/road base/modified gravel/whatever your local term is–then there really shouldn’t be voids for your stone dust to travel down to.
I have never once laid landscape fabric between the gravel foundation and the stone dust bedding. I used to lay landscape fabric beneath the gravel–and I still do in wetter conditions/if I have any reason to want greater stability then normal. I well compact my sub grade, well compact my gravel base, and I do not worry about transmigration of soils.
My older flagstone patios that had a layer of fabric beneath the gravel, are in great condition, still. My newer jobs, from the past 5 years or so that usually forgo the fabric, are also in great condition.
Fabric: usually, not so critical. I’ll use it if the area has a lot of ground water. Or surface run-off. Or if I’m limited in how deep I can go with my gravel. Or if the area with have vehicular traffic. Or if there are trees nearby that have aggressive roots–anytime that I wish to give the gravel foundation more stability than is normally called for.
Thanks Devin, that’s exactly what I was hoping to hear. The base rock must be a CA term for crushed rock and stone dust mixture and it compacts quite well. I felt like I’ve built myself a small version of a Roman Road so I think I will forgo the fabric as well. Thanks!
I have a flag stone area in my back
Yard. It’s been there for four years. The weeds keep coming up through the sand. I have used different sand and would like to know what to do. There was never a fabric cloth used by the professionals.
I have taken the sand out of the seems and have all the weeds removed. What can I do next to ake my area look great again
Re-fill in the cracks between your flagstone with stone dust and if weeds ever grow there again, just pour boiling water on them to kill them.
Weed fabric underneath your flagstone will not help really anyway. Any weeds that can live in sand and that have roots that will penetrate beneath the sand and the gravel, will already have a few inches of root buried and will live in spite of the fabric….and if the root got that far down anyway, the root is probably tenacious enough that it will laugh at the weed fabric and got right through it. Stone dust is a better material for your flagstone joints than sand, and boiling water will handle weeds. Good luck with your flagstone!
Devin, you have some really good information here! I think I’ve read your articles now about 4 or 5 times! You’ve already helped me so much, but I may be calling in a couple weeks about the filling between flagstone. It just all makes good sense what you’re saying about the base and the use of screenings. You saved me already with going with the contractor’s polymeric. I don’t have him anymore.
Hi Devin,
I have been in our home about a year (Triangle area, NC), and thought I was being smart and saving money in the Fall when I had a lot of yard leveling done – they had machinery so I had them dig out our 520 sq ft patio area. Has been a nightmare to keep it dry, and been largely having to pump water out whenever it rains. Only partially successful, and it’s pretty muddy back there (red clay).
How dry does it need to be before they instal the patio to avoid settling etc in the future?
Also, being told that gravel base (vs concrete pad) will eventually get sink holes beneath it as water drains through it. Is that right?
Thanks!
better get that clay soil pretty dry. Dig it out with a steeper slant and remove anything that may be obstructing the downhill flow of surface water. And let it sit for weeks, if you can.
Probably, the soil will simply need to be excavated further, until you hit stable soil. The subsoil, the earth beneath your foundation should be stable and well compacted. Dust won’t compact, too dry. Wet clay is doughy and no amount of tamping will help. Trying to lay gravel on top of damp, doughy clay just does not work.
To lay a gravel foundation on top of wet clay, you will have to dig down. About as far as it takes. Might be a foot down. When the soil is starting to get more solid, less spongey, you can then lightly tamp it. Or let it sit in the sun to dry for a few hours, and then tamp. Lightly is key, with damp clay soil. Tamping it too hard will just make the situation worse.
Now take the dryer soil from your excavation and add gravel to it and mix it up a bit. Lay four inches of gravelly soil, then lightly tamp. After laying a few gravely and/or drier lifts, your soil should start feeling a bit more solid underfoot, getting more solid at every lift.
Your actual gravel foundation should be thicker than usual. Say 8″ maybe. By the time you get to the top couple of lifts you should be feeling stable. The stability test: tamp the soil/gravel. Step there. Kind lean/bounce from foot too foot.
The stability test is what it is all about. The whole thing you are trying to avoid is a spongey foundation. What you are looking for is for it to simply feel nice and sturdy underfoot.
I’ve gone to build lots of patios on days when the soil was too damp to get it to properly compact–and the above is about how I usually handle it. Numbers are approximate, you have to do it by feel.
Reiterating more simply:
dig down a foot or so and lightly tamp.
take the dryest soil you have and mix it with gravel. Spread it out and lightly tamp.
lay four inch lifts, lightly tamping each time.
Then lay straight gravel, deeper than you normally would.
As for your last question, well, for my opinion on the matter of gravel foundation versus concrete foundation, I direct you to this post:
http://tinyurl.com/pcvry4z
Seriously, sink holes? You should also beware of quick sand and icebergs. Have heart then, for a well built dry stone patio will serve you for decades in good stead.
Hey Devine, first of all thanks for all the informative posts! I live in Southern New Mexico where unlike PA we may not have the extreme cold (although we do get below the freezing mark), but do get extremely dry heat which has the adverse effect on concrete in which it will expand slightly. So I am about to lay some flagstone in my front yard which is largely xeriscape, but have a couple of concerns that I was hoping you could help ease.
Part of the flagstone will be on a slope, and I am worried that this will cause issues if I utilize only screening/stone dust. I have seen instances where the stone dust will shift down ending up near the bottom of the slope leaving a mess covering the bottom flagstone and the top flagstone spacing empty. Any way to avoid this?
Another issue that concerns me is that in my region we get extremely high winds, which not only carries in a lot of fine sand, but will also move out a lot of the finer materials. Do you believe that this will this cause any cosmetic or functional issues?
Lastly due to my xeriscape yard, in order to remove leaves or other debris I must use a blower to remove from the gravel, and am worried I would find myself constantly refilling the stone dust after maintaining my yard, should this even be a concern?
Thanks again,
Adam
Adam,
1)
I really can’t say. How steep is the slope? Anmd how much rain do you get? Around here, it rains a lot…and I rarely lay flagstone on a very steep slope anyway.
2) I have many times used a leaf blower to clean debri from a flagstone patio. The stone dust stays put. I’m not too worried about winds removing the fines–you hose down the patio when you are finished installing and the stone dust “sets up”–the fines bind together.
In this case I’m also going to recommend that you talk to some local guys and/or do your own research and experimenting–I know, you are researching right now, right?…what I’, saying is that I really do not have any experience laying flagstone in the desert.
You should get a prize for stumping me. Email me your address to claim your prize! (I’ll give you a hint…it’s a Devine Escapes t-shirt)
Anyway, good luck and happy flagstoning!
Hi Devin, I am in pgh pa. Wondering what depth of gravel do we need under the flagstone? We ate planning about 100 sq foot walkway. Don’t think that pgh is traveling the globe but depending on cost we would definitely have the space to have you stay here. …. And it may save our marriage. Hahaha!
Approximately 4 inches of gravel beneath the flagstone. At 100 sq ft, you’ll want to get about 2.5 tons of gravel road-base aka modified gravel. If you wish to have me over to help with the project, then you should send me an email and we can discuss the matter.
Hi Devin,
We just removed an above ground pool and now have this 24′ circle of sand. We would like to install a flagstone patio and was wondering if we could do that right over the sand, or if we have to remove all of the sand (uuuugh) and put gravel down first? The pool was there for approx. 14 yrs so the sand is pretty compact and level. I’m not sure how many inches of sand is there, if I were to guess maybe 4″. We live in upstate NY where winters are pretty brutal. I just want to do it right. Thanks in advance.
You are saying “ugg” at the mere concept of removing 4 inches of sand….well, building a flagstone patio is hard work. A lot of it.
Get that sand out of there.
And read this article: https://www.devineescapes.com/flagstone-what-to-use-sand-cement-or-gravel/
Ants love sand. Sand with bricks or stone atop it is a big flashing neon invitation to ants who go marching a thousand by a thousand and they all go down to the ground, to excavate your patio! You have your flagstone sitting right on sand and then they will undermine you, and within a few years you will have flagstone with big voids under them, and it will be a big big big problem.
Best of luck! If my advice is at all helpful to you, then please share some of my gallery photos on whatever social media you use. Thanks 🙂
Devin,
Just tore out a couple of bushes and have about 60 square feet consisting of 2 “holes” bounded by concrete patio (Dallas area so it’s clay). Wanted to put flagstones in so I excavated (only to about 5 inches) and laid 2 to 3 inches of crushed granite with the intention tamping and putting flagstones on top with something like larger crushed granite to fill the large joints. Before I could get the flagstones on top of the crushed granite base, we received 100 years worth of rain in 2 weeks. It’s drying out now but is very spongy in places. Any options other than rip everything out and dig deeper?
Thanks,
Soggy in Texas
Soryy, but yes, you want to dig deeper.
I can’t tell you exactly what I would do, because I am not there to feel the soil as it is worked, but often, it goes kinds like this for me:
Dig down 6-12 inches deeper then I usually would. mix up the recently excavated subsoil with stone dust/gravel/whatever. Mix it up good. Tamp the excavted area LIGHTLY. The harder you tamp, the spongier it will become. You just end up vibrating the moisture upwards. Lay a few inches of the soil with gravel mixed, and then tamp that LIGHTLY.
Keep building it up in 2-4 lifts. First lift or two might be the driest soil you have on hand mixed with gravel. Higher lifts will be all gravel/stone dust. As you go up, lightl;y tamping at each lift,, it should be getting less and less spongy. If you get to the top and the soil still has a springy/sponginess to it, then you may need to just let it air out some more, bake in the sun, for up to a week even if it’s really bad. After a time, come back and re-tamp, lightly, again. If rain comes in the meantime, you may need to tarp the scene.
If you dig deep enough and tamp lightly enough, then you will not have to wait, but it will be solid enough when you get to the top. But if you do need to wait, then you’ll want to tarp the scene if more rain comes along.
Okay, fine. The other trick I’ve learnt is landscape fabric. The spun fabric stuff, or the stuff that feels like felt–NOT the woven stuff and certainly not the woven plastic stuff that’s just like silt fence. In the very worst of cases, I will lay some landscape fabric/filter fabric, in between gravel/soil lifts. maybe 2 layers of fabric, for the who think–maybe only using the fabric on the most persistently spongy spots. The fabric just disperse the soil movement out further/disperses the weight load–just a bit.
Good luck.
Please like and share some of my work on facebook/social media/tell a friend kind thing. Thanks!
Hi Devin,
I’m getting ready to dry lay a flagstone patio (using an IndianRidge product that is cut and uniform to 1″ thick). This patio would butt right against the house and adjoining, existing concrete patio. Anyway I got mostly through the excavation and my wife asked if I could use the same stone to cover a bit of concrete patio.
So, from what I have read, this can be done, but the base layer for the patio must be really well compacted and aligned. Then screed the whole thing and lay stone (using glue or mortar to hold the edges on the concrete).
So my question really is can this be done? Is it wise? Are the 1″ thin stones prone to lifting in the past over the concrete?
Thanks!
Having not seen the concrete pad, nor the stones you are using, I offer you my best take on the situation. Use your own judgement though, for sight-unseen, I can’t say anything for certain. Your mileage may vary is what I mean to say.
Well, if you were to cement the flagstone on the outside, and lay the inner flagstones just in a bed of stone dust, then you’re not leaving a place for the water to go. Water gets under the flagstone, and flows down atop the concrete pad–but then gets stuck when it gets to the edge of the concrete patio, because it encounters the cemented in stones and can’t get past.
If the stones are cut stones, to uniform thickness, then they can probably just be laid flat on top of the concrete pad. Glue the outer ones and dry lay the inner may work…but if the inner stones have a wobble, even a minor one, you may just want to glue all the flagstones down. Any exterior masonry adhesive will work. Make sure the patio and the stones are both fairly clean. You’re not covering the entire underside of the stone with the product, the water is able to move around the glue and keep flowing.
EVEN BETTER solution, if the cut stones are large enough, and you have enough patience and ability, then you can possibly just lay the larger stones on the outside edge of the patio and lay them dry. Lay them all dry. A mix of small medium and larger stones on the inner part of the patio, larger stones, ones that are too big to pop up under foot, go along the outer edge. That’s how all my patios are built really–dry laid, with large ones on the outside. No glue, no edging, no cement.
1 inch stones are a bit thin, for dry laid. I prefer 1.5- 2.5 thick for dry laid flagstone. But, if they are saw cut and the foundation is screeded nice and perfect, then the stone can be made stable underfoot. Just make sure foundation or bedding material is perfectly smooth, and gently mallet each stone into the bedding material. Stones less that 1 square foot in surface area will be prone to not sitting stable.
Best of luck! Take your time and don’t get mad at the stones 🙂 and I’m sure your patio will turn out great!
Polymer sand between irregular flagstones was a new concept for our installer about seven years ago in Prince Edward County Ontario Canada (peninsula in the eastern end of Lake Ontario) when we put in our patio. Our contractor didn’t do a lot of research into the process and the sand started almost immediately to lift in patchy pieces from from the joints. We now have a mess of weeds and polymer sand left in the joints. The flagstones are solid and aren’t shifting but it looks very messy. We are in the country and weeds are a major problem. I’m looking for a solution that will be neater and easier to maintain going forward. From reading your articles I am guessing I will have to remove the polymer sand filler and refill with screenings. My question is how deep should the area be between flagstone before adding the screening. When the polymer sand lifts out, it’s only about 1/4 to 1/2 inch deep (gravel below). Short of redoing the entire patio which is a last resort, can we rescue the flagstone joints with screenings after removing the remaining sand?
I’d prefer it if you had a good inch of screening depth…or better yet, screenings all the way down to the bedding material. Still, a half inch screenings depth between your flagstones will work better than a half inch bed of poly sand, any day. Poly sand will require a greater depth–and will be more of a headache when it fails.
So just clean out your polymeric sand from between the flagstones as planned, and sweep in screenings and hose down, let it air dry, then top off with more screenings and hose down again.
It might be fine, but it might not really succeed so well. Like I said, an inch deep is better, so you may want to spend some time to manually pull out some of the gravel on the higher spots. Knees pads wear knee pads.Hire a local kid to spend a couple hours doing this simple, tedious task–or just gt into it yourself. Play some tunes you like and pull out one stone at a time 🙂 Or just sweep in for the first try–if it fails, top off with screenings….if it fails thrice, then you know it’s time to pull out gravel, one stone at a time.
Best of luck!
Can I add small rocks of my own selection to my polymer-modified sand in between my flagstones? Is it strong enough to bond with them so they don’t dislodge and leave holes in the joints? I am thinking about filling the joints almost all the way with the polymeric sand and then pushing a thin layer of very small 3/8″ – 5/8″ rounded black gravel (Mexican beach pebbles) on the top and sprinkling more polymeric to fill between the pieces of grav el.
Any words of wisdom you can offer will be appreciated.
I do not recommend this. First of all, polymeric sand is prone to failing–as described in the above article, and many of the replies.
Adding the pebbles to it is just adding another weakness to an already failure-prone system.
To achieve the look that you are talking about, the best that I can offer is 1″ river pebbles, with stone dust around them. I have used river pebbles, 1″ in size, filled the flagstone joints with them, then sweep in stone dust over the same joint. Hose down, the add more stone dust to replace that which has settled. This method is a bit trickier and may need more maintenance, then the simple stone dust method. Still, it is much better than using polymeric sand for your flagstone joints. In my opinion that is 🙂
Good luck, whatever you decide to go with!
Hi Devin,
This is all great info that I wish I had found when I started re-doing our patio! We live in the northeast and had to tear out the old warped and cracked cemented flagstone patio before starting it over. I used the methods you described and just finished leveling all of the stones and have the grit used for leveling swept between the joints. My question is about raised patio edges… Ours is about 4″ taller than ground level on one side. I was going to cement a small barrier wall to keep the screenings from washing away under the stones on this side but was wondering what method you use to finish a slightly raised edge like this? Thanks
Well, my raised patios are raised upon very well built stone walls.
And the flagstones that come out to the edge, the stones on the edge, are thick–and set very stable.
These flagstones at the edge of the patio, the stones touch at the joint. You know what I mean? The joint gets real tight, at the edge. Grit CAN still wash away. And will. In my experience, the grit at the edge needed to be topped off a couple of times, but then stabilized.
I’ve returned to a raised patiop like that, years later, and seen most of the joints still filled, at the edge, but a couple joints were kind of empty, like for the last 3-8 inches, near the edge. The owner had not topped them off because…it really caused no problem at all. And I could see another trick I’d emplyed too–the joints near the edge had gravel in them. Grit was swept in around and on top of the gravel, but a few chucks of gravel were in there too, to kind of slow down the washing away of grit.
Based on all this, you’ll never see me resort to cement in this situation.
There’s other ways to go about it. My way is simple, patient stone placement. Some maintenance will be needed. If you go with cement….you MAY avoid needing to do maintenance. Down the road however, the cement maintenance may end up being more of a headache, then dry stone maintenance. Hey, you chose to go DIY, so it will be a learning experience, way way or another!
Good luck, and enjoy your patio 🙂
Hi Devin,
This site is awesome! You’re incredibly detailed with your responses too.
Okay, here’s my situation. We’re hosting a wedding in our backyard here in Toronto, Canada. I’ve got a ton of stuff to do in the next six weeks and in some cases, I have to take shortcuts just to get it all done. I have a 12′ by 12′ patio built with 2’x 2′ ugly old pink and yellow concrete slabs. They’re very solid; about 2″ thick. The patio was professionally built many years ago with a little interlock retaining wall around it, weed cloth, and limestone underneath. Very little shifting of pieces seems to have occurred, though I’m aware that the freezing and thawing process will continue to have an affect.
I know it’s not the right way to do things, but I’m going to lay flagstone in mortar on top of these. I spoke to a very, very experienced mason friend of mine about this and he said it might work and it might not. (Unfortunately, I can’t get in touch with him now.) I’m assuming that if it does work, I may have to fix the grout once in awhile and I’m okay with that. I’m also thinking that, if it doesn’t work out great, since all the stones would be cut in their mosaic, I could take them up, get the mortar off, then do it right next year without having to worry about the cutting part of the process since that would already be done (although I’m not sure how hard it would be to sufficiently get the mortar off).
I’d love some general comments about all this. In addition to that, one other big question I have is this: I saw another guy on a video who dealt with a a major crack in a concrete slab by using metal lathe to bind the concrete together before putting flagstone on top. Should I consider doing this to bind together all these 2×2’s? If so, could I do it just along the seams or would i put it on the whole 144 square feet?
Thanks! -Jay
Due to the intense volume of blog comments, calls, emails and texts that I have been receiving, I can walk you through any flagstone or patio repair or installation challenges that you may be facing.
https://www.devineescapes.com/phone-consultations/
Yes, my responses were rather detailed 🙂 but sorry, I just can not possibly continue to offer up that service for free.
Good luck with your flagstone! If you need help beyond just my articles, I take paypal 🙂
I have an existing concrete cap that is 630 sq feet. Then I’m extending half of the perimeter by 7-8 more feet. Using large Pennsylvania Fieldstone that I bought here in Atlanta area. Over the concrete cap, we’re mortaring it in. Over the soft ground perimeter extension, we’re using crusher run under.
Originally, we thought about mortaring in joints between stones. Decided I want consistent grout lines… I’ve started filling with slate mini chip. This is about 1/2″ pieces. the supplier told me this would work, but I’m having doubts. I’m seeing your recommendation here to use “screenings”.. Can I go back and top over the mini chip with screenings ? I’m concerned that the chips will not be as stable as I want. the mini chips do sweep in and fill nicely. Also, I get even better drainage, as water seeps down the mini chip grout lines. Any advice here? I love Flagstone !!! (new love always the best) Happy to send photos of my job in progress.
FOr the best results, I’d recommend that you get them chips out of there and replace with screenings.
If you want me to go over photos and advise further, that’s cool, but I’ll direct you here first:
DIY flagstone consultations
Than you and best of luck!
Hi devin,
How thick should my base be? GoING to use modified and top off with stone dust to level. I live in PA so you are aware of the climate.
Four to six inches.
I have heard of people using a 1/12 ratio of portland cement to screenings/grit for both a setting material and joint filler on dry set bluestone patios. Is adding the Portland really necessary?
In a word–no.
Might create problems. The again, a ratio of one part cement to twelve parts screenings…um, it might be alright.
My feelings are that it will A) be too rigid and crack. Or it might semi-solidify in the way that it is intended. IF it actually does that then I certainly foresee problems. Or else b) it just won’t make the screenings bind up much more than they already do.
“when you use screenings for both the leveler and the joint filler you are creating a good scene. If there is ever any minor issue with the screenings underneath the stone it shouldn’t matter too much because the joint filler will settle down and fill the void beneath the flagstone. Having screenings up top and down below, it just works out well.
You can expect to top off the screenings once within the first year—a small bit will settle or wash away. No problem, just sweep in some new material and you’re good. After that, in future years, you’ll be fine. My best recommendation is that clients hire me to do maybe a couple hours maintenance once a year—by no means is this nessesary, but I like my work to sparkle.”
The above quote is from this article.
In conclusion, the system that I use, where screenings serve for both under the flagstone as the leveling agent, and for the flagstone joints too, works The 1-12 cement notion might work alright…idk. But I’ve observed my patios over the course of more than a decade. My bet, and I will put money on it, is that the 1-12 system is much more of a maintenance hassle over the course of years–much like the poly-sand method.
Devin, Enjoy reading all your advice. I do get confused with the different materials. Making a 180 square foot area as a walk way. Live in San Jose California. Some rain , rare freeze. It had weed block and 2 inch river rocks in place . River Rock a little wobbly under foot as a daily path . I removed river Rock and old weed block. I have 2-3 foot gray flagstone. Should I use granite gravel 1/4 inch as base, then flagstone with granite fines. Gaps are large 2-6 inches . Was concerned about placing smaller rocks between flagstone- can get messy. I could replace the river rocks between flagstone? The current dirt is quite compacted from the heavy river Rock resting on it, is 1-2 inches of base gravel good? Thank you for your expertise.
Sorry for the delayed response! My software had misidentified your message as spam, so I ignored it. My mistake!
Anyway, You have a lot of questions. You seem to need help, from square one. I could help you with a phone consultation Or I could just direct you to read more of my blog posts.
Anyway, I’ll try my best to help here, if possible:
4 inches compacted road base
An inch or so of granite fines (screenings) for leveling the flagstone
No joints wider than a couple inches
Screenings for in between the flagstones.
That’s how I build ’em. Individual taste preferences, unique site conditions, and local material availability can all factor in as to why you might vary from what I’ve suggested above.
Best of luck!
Read more of my blog, stuff like this:
https://www.devineescapes.com/category/how-to/
Or contact me for a phone and/or email consultation, if you still are unsure of anything 🙂
Hi Devin,
I have a question for you about screenings. We had a patio installed
using irregular Tennessee stones (I don’t know if that’s it exactly, I
know it’s Tennessee something or other..). They tried using Techniseal
polymeric sand, but it would not set. I think the first 2-3 times they
tried it, they didn’t use enough water, but I’m not sure about the 4th
and 5th tries (yes, that many). In some areas it remained spongy and
anything heavy or sharp would break through. Since they’re tired of
trying, I’m told they’re going to use screenings in between the joints.
Is that okay?? Because we have irregular shaped stones, some of the
joints are quite large. I’m concerned about having loose gravel coming
out and making a mess, making it not good for bare feet, having the dog
track it in the house, etc. Not to mention that I don’t like the colors
available. Can you help, give advice, tell me all my worries are for
naught, anything? Thank you!
Polymeric sand is not good stuff.
Screenings are the right thing to use.
If the joints are “quite large” as you said, then it may be a problem. That’s why I take my time and get the stones to fit nicely, with joints that are about an inch wide or so. Whether or not the wide joints will be a problem for you, I just can’t say. Site conditions, how wide the joints actually are, how big the joints are in relation to the flagstones, and other site specific factors would have a bearing on that.
When the joints are too big and/or they are over filled, then screenings can get all over the place and be a bother…sometimes I’m called in to fix these situations. Usually, I end up spending a day or so re-fitting the stones and making them look like a skilled flagstone guy did them.
Anyways, that’s about the best I can offer you here. Good luck! If you still need more flagstone or hardscape related advice, you can email me photos and set up a 1 on 1 phone consultation.
Sure wish I had read this 3 years ago before someone convinced me that they could relay my flagstone walk and put material between the stones so it would not be a trip hazard. Well, the put in Polymeric sand and it’s worse now than it was before. And I’m out $700 because they warrant their work 1 year. It was only 1 year and it was falling apart. I can scoop out that “sand” with a plastic spoon. Now I have a ton of work to do and I’m afraid the stones were reset too far apart and the gaps are so big nothing will last very long.
Thanks for your site – just trying to find a new and better solution!
Sorry to hear of your flagstone troubles! My recommendation is that you fit them flagstones a bit tighter, 2 inches or so will be alright, and then sweep in stone dust.
Laying flagstone when you’re frustrated is not the way! Flagstone responds much better, to a happy jobsite. If it were me, I’d wait until you have a weekend free, without any stress on your mind. Play some music that you love and enjoy your time outdoors.
Good luck with it then!
I’m also a member of the ‘no plastic in the backyard’ group and use only organic lawn care. So here’s my problem. I have two patios of natural irregular flagging stone that was laid on gravel/sand about 12 years ago. The joints are fairly large in some spots so it has a very ‘natural’ feel to it. Considering it’s NY and the crazy weather we have here, it’s held up really well but about 3 years ago the cement joints started cracking and lifting out and the weeds started growing. It’s so messy now that we finally decided to power wash and refill the joints. I won’t use the poly sand stuff but know if I use cement again I will have the same maintenance issues. I like your idea of using screening, it would give me exactly the look I want, but:
1. As one patio surrounds a pool I’m concerned that the screening will come out and make a mess in the pool- either carried in by foot or wind.
2. The dog will bring too much of ‘the outdoors’ in!
Any thoughts?
1. Screenings getting out and getting into your pool…..is a common worry, but done right, it should be no problem. First of all, your flagstones should be graded away from the pool already, right? If not, then that needs to be fixed…but so long as the flagstones are pitched properly, then you just need to do two things: do not overfill the joints with screenings. Leave the joints an 1/8th of an inch to a 1/4 of an inch low. Hose them down real well, add more screenings if need be…even fill them basically flush with the top of the flagstone, but then hose off–and they’ll settle.
Hello Devine
First like to thank you for all the detailed answers you provide. I live in cedar mountain nc and I’m about to start a dry lay flagstone patio. This area is a rain forest and with that in mind was thinking to lay down 4″ of 3/4 gravel and than lay another 4″ of crush&run to be compacted and on top of it 2″ of screen for the flagstone.
Do you think my 4″ of 3/4 gravel is a good idea or necessary. Thank you
Well, I can’t say that it’s necessary, but it probably can’t hurt.
I haven’t built any flagstone patios in N.C yet, but I imagine freeze-thaw is a lot less of an issue for you than it is up here in Pennsylvania. Hmmm…
The 4 inches of 3/4″ clean gravel (without fines) underneath the crusher run….first of all, if I was putting clean gravel beneath the crusher run/road base for a patio, I’d make sure there was a good filter fabric (not weed barrier) between the two types of gravvel, so that fines can not migrate down into the clean stuff. One concern that I do have….you may be creating an underground pond with your system. Water would just sit there, in the voids….not that that would hurt anything, per se`.
Okay, sight unseen, here’s what I’d consider doing: just lay an 8″ base of crusher run. Forget the clean gravel. The crusher run (here in Pennsylvania we call it “modified gravel”) will drain pretty well on it’s own.
I’d consult with someone local to your area though. Better yet, pay someone, a landscape designer or a contractor, to come out and offer their own advice. In all probability you’ll be alright with the 8″ foundation. Lay your flagstones pretty tight, build the patio with a good pitch– 2.5 inches of fall over a ten foot span–and you should be alright. But I’d have to see the site, to say that with great confidence.
Good luck with your patio then, and I hope that helps.
Hi Devin- I’m trying to use up scrap pieces of quartzite flagstone from my main patio to make a small patio in So. Cal. I have clay soil that’s packed down from holding all the stone and spec-mix. Being on a hillside I decided to cement the outer edge on a small retaining block wall. I was going to set the rest of the stone in sand, but after reading your advice I am stumped. Please advise.
Thank you.
Just set your flagstones on stone dust instead of sand. I’ve written other articles, like the one I’m linking to below, that explain how I would go about building this type of patio–but in your southerly location, freeze/thaw is not an issue, plus, you’re already like half-way built, so maybe you can just get away with replacing the sand with stone dust. Might have some maintenance issues down the road though….. https://www.devineescapes.com/flagstone-what-to-use-sand-cement-or-gravel/ Also, I make myself available for phone consultations, if you do want to start all over again and have someone walk you through it. Best of luck, and I hope that helps!
Hi Devin.
I was on the lookout for some used flagstone here in Toronto Ontario. A demolition sale has offered some, but of course I would have to remove them myself.
Do you have any experience in removing flagstone, keeping it intact for reuse? Is there any way to tell by a picture if it would be easy or hard? I dont have any special tools, just the usual stuff.
Here is a link to the stones I am thinking of bidding on: http://maxsold.maxsold.com/auction/1699/item/flag-stone-c-160533
All help greatly appreciated.
Sure, these flagstones should pop right up for you, with little risk of breakage. Nice thick stones, with little or no spalling/delamination. The steps give you a nice lip to get started from–you start removing flagstones at the steps–cause it’s easier to get a pry tool or chisel under there. .
Your hard part will be weight. These flagstones look like they might be 2″ thick and near 2’x3′ in surface area. Bring a hand truck/dolly with you and maybe a helper to get them up on to the truck. Chances are that only the stones on the edge, the ones at the step, are that thick–and the inner ones thinner. As a matter of fact, I think I’ll buy these stones myself.
j/k, but if I was local, you’d be bidding against me.
Pickaxe/moddock, pry bar, digging bar, chisel, hammer… should be all you need. Good luck!
Devin:
We’re preparing to lay a 17’wide x 33’long quarry stone patio in northwestern Montana. Our new home sits on the side of a mountain and we have a compacted 4″ gravel base already in place from the contractor, (Underneath this base is the “native soil, which is actually a mixture of natural Rocky Mountain granite rock, gravel, along with some clay mixed in for good measure). The gravel base installed by the home contractor currently has a “fall” of 1/4″ per foot on the 17’patio width). The cut quarry stone we are planning on using is “Montana Ledge Stone” that is of various widths and lengths, but all are approximately 3″ to 3 1/2″ in thickness, (and heavy).
We were thinking of using a 3″ thick “leveling” layer of stone screenings between the gravel base and the 3″ Montana Ledge Stone slabs and filling the voids between stones with stone screenings as well. Would appreciate your input as to whether or not this approach would provide us with a solid patio structure with minimum maintenance over the coming years.
It’s not exactly the way I do it, but it sounds good.
What I’m usually doing is 4-6 inches gravel, then 1-2 inches of screenings. But I’ve seen other methods for laying flagstone, some of which work pretty well. I used to work with a guy who laid flagstone like this–a 4 inch bed of compacted screenings, then a 1 inch bed of loose screenings for the leveling. I’ve seen a walkway built like that that was 10 years old and was sitting nice and level still. That way might not be best practice, but it’s not terrible.
4 inches gravel and then 3 of screenings? I can’t speak from experience, but it sounds alright.
Devin, very informative site. We have followed your recommendations and we have a great looking bluestone patio (various rectangular cut stones). The only problem is the screenings used as the joint filling do tend to displace to the stone surface – painful for bare feet! And untidy. Our joints vary but average half an inch wide and the screenings come to about the same distance from the top of the stone. Patio is only one year old. Question: will the problem become less as time goes on? One issue was the landscapers were blowing the patio after lawn cutting and that caused screening displacement. But it still occurs naturally though not as bad. Thanks
Honestly none of my customers have ever complained to me about this….but then I do spend quite awhile hosing the patio down when we’re finished.
Yes, over time the joints should stabilize, needing to be topped off less often, and spilling out unto the flagstones surface less often.
Devin,
Looking to do a stone walkway, approx 30×3 ft. I live in Vermont and we get some rain, but the ground is firm and no drainage issues. Curious what your thoughts would be for an appropriate gravel and screenings depth would be. I planned to put a layer of fabric down first. We are looking to use smaller irregular rocks, min 1 foot size. Thanks.
So an update. I dug it out today and encountered quite a bit of sand at 4-5 inches and below. I went down a total of 12 inches. I plan to get crushed gravel for the base. Can I reuse this fine sand for a layer above the gravel and do a finer mason sand for the top layer?
Hey Devin. Somewhat of a brief question. I have a concrete patio that is about 40+ years old, in decent shape besides a roughed up surface as far as chips(no major cracking). I am looking to dry fit directly above the existing patio with flagstone about 1″ thick. The existing patio is graded away from the house.
Should i take any measures to ensure proper drainage if i am laying over screening and dust between joints as you recommend?
Also about how thick of a layer do i need under the stone?
Thank you so very much.
Mike From PA
This is not a quick question…sorry. I’d need to see photos and spend some time on it. https://www.devineescapes.com/diy-flagstone-help/%
I can tell you that 1″ is a bit thin for dry lay…1.5″ inches is recommended.
I removed an above ground pool a couple years ago and have kept the liner lying in place to save the sand that was under the pool for almost 20 years. I’m now ready to make that circular area into a flagstone patio. Would you consider the sand base to be adequate for the patio given that it was in place for so long? My plan is to level the sand and add some sort of gravel for between the flagstone OR what do you think of grass between the flagstone? I’m doing this myself with a little help so easy is good.
This depends on how deep the sand is and what the soil underneath the sand is.
If it’s clay subsoil, or otherwise mineral soil–not organic soil, then yeah, the soil can be considered stable at this piont.
I’m not a huge fan of sand as a flagstone patio base because ants love it and might undermine it..but sure, it can be used. Just might have some maintenance in the future. But how deep is the sand? I would not recommend using sand more than a couple inches deep. You have to decide on how easy you want your patio to be to build…and how good you want it to be. Get rid of the sand and replace with stone dust. Use stone dust in-between the flagstones, as described in the article–and others on my blog. If you want to cut a corner you can skip the gravel and go straight to stone dust/quarry dust/decomposed granite/whatever they call it in your area. Since your soil has sat undisturbed it will be stable enough you can get away with skipping the gravel…cut more corners than that and your patio will maybe just not stay nicely level. Your call. Good luck! More help here https://www.devineescapes.com/category/how-to and here https://www.devineescapes.com/diy-flagstone-help/%
Hey Devin, found your blog just in time. We just moved into a 150 year old heritage home and have a flagstone walk and patio for the first time. I’ve laid miles of pavers but never did flagstone. The previous owner put sand between the joints then, at some point, put polymeric sand over top of that. Needless to say, it failed-but came off in large satisfying strips. I pressure washed the stone and the great colours were revealed from the dingy dirt for the first time in years. My problem is what to put in between, like many of your readers. Your work (which is awesome) have quite tight joints, my flagstone joints are quite far apart. Would the screenings still work with areas over 2 inches? I did consider pulling the sand out (which I will probably do anyway-beneath the stones themselves is screening material) and replacing with soil and putting in thyme or some creeper like that, but I’m a little indecisive about what would be best in this situation. Right now it is a bit of a pain pulling a chair over the patio, because it gets caught in the flagstone. I guess I could always try to tighten the joints. If you have any thoughts on this, I’d really appreciate it.
Sight unseen…I’d probably still go with screenings. With 2 inch, or 2 inch + gaps between your flagstones, it will need a but more maintenance than the tight joints I usually have…will likely need to be topped off more than once within the first year. Might need another top-ff during the second year…but should stabilize and probably be fine anyway–provided the patio is pitched properly with no major dips/puddle areas. Stone dust might escape to the surface of your flagstone though…and get tracked inside. This will happen less though, if you avoid the common mistake of overfilling the flagstone joints. more on that here: https://www.devineescapes.com/taking-care-of-your-patio/%
Also, steppable ground covers can often be planted right in screenings. Moss for example will do fine in plain screenings/stone dust. I’ve seen thyme do well, in a mix of 2 parts stone dust 1 part topsoil.
That’s really helpful. Thank you for taking the time. I think I will do the ground covers in the front and what you suggest with the screenings in the back. The patio drains quite well, with no major dips, so it should work out. Cheers, A.
Hey…so I thought I had already responded, but maybe not. Sorry, busy time of year for a hardscape/masonry guy, lots of DIY consultations, site consultations, design work and actual hardscape installation work going on in my world right now.
Yeah, I’d pull out the sand and top off with screenings. Screenings will work with larger joints…but will work better (less weeds, less wash-out and better looking) with tight joints. So if it’s not too much trouble, you might consider tightening those stones up a bit.
I hope it goes well for you.
Hi Devin:
I’ve been told that we can/should use half inch clean/washed stone as our six inch base because it doesn’t require tampng and allows for good drainage. We live near Toronto. Do you think this would be fine or should we insist on three quarter inch gravel?
Thanks for your help.
Tom R.
Clean gravel does not compact.
Modified gravel is what we use…. half inch versus three quarters is not really the issue for me. My concern is the lack of fines. For a proper dry laid flagstone foundation, I want the gravel to be firm and compacted–that means it must have fines. I’ve built patios on quarter inch minus–meaning the largest stone in the mix was passed through a quarter inch screen–the “minus” indicating that the gravel was graded to included all smaller sizes–down to the all-important fines. Flour like stone dust, that binds up when damp and makes the gravel compactable.
…but maybe it’s okay to used clean gravel. Maybe this guy has a technique I’ve never heard of. Me, I’d ask to see a portfolio and/or for references.
Best of luck!
Hi devin, my husband and I are building a firepit with a patio around it made of flagstone and we have never done it before. Im wondering if u have any tips for us as far as if we should compact the ground and what to use for the foundation. The area we are using was leveled a few years ago with sand for a pool but of course the grass and dirt have grew back throught the sand over the years of not having the pool up. We live right behind a granite quarry so there is alot of granite around and under our land. I would greatly appreciate it if you could help us out with some tips.
The above article kind of answers that question…
Dig down, tamp, lay gravel. Road base gravel.
I offer consultation services, if you need individual guidance.
Hello Devin,
Thank you for the blog. I see lots of questions for flagstone patios and such. I’m relatively new at yard DIYs so when I built my patio I decided to do it out of pea gravel. However, it is very loose and constantly moves under you. I was wondering if I should put some sort of sand mix in to keep it sort of compacted. Patio is 19×15. In Milwaukee , Wisconsin. Can get very cold and lots of snow.
Hey Devin,
Awesome site! Read almost every word on it….and plan on using your technique to the tee! Love the color scheme of your patio with the white bench on this page. Can you tell me what you used for the joints for the lighter color? My local quarry only carries bluestone screening which is what I plan on using for the base of my 140′ walkway. The flagstone I chose is med/dark brown and I’d like a lighter joint.
Thanks for any advice.
The lighter color screenings are limestone screenings. It’s actually not recommended as a base for flagstone, because it holds on to water longer than other types of stone dust. It’s somewhat clay-like. Makes a good joint material though. I rarely use it, but when I need it, I just call around to landscape supply places and masonry supply places until someone has it. I know I could go to the limestone quarry–but I believe they have a minimum order that they’ll take, and I’ve never needed more than half a ton.
Good luck
Hi Devine, I love all this flagstone info -thank you! We bought a house a few years ago with a pretty ugly concrete patio that we are planning to cover with some Pennsylvania blue stone. I was thinking of bulding a treated wood surround, then using about 2 inches of screening for base and gap filling material. What do you think? Am I on the right track?
Thanks again,
Mike
You stand a good chance of experience some significant settling and heaving of your flagstones with such a small amount of base material. Really, it somewhat depends on what your soil is like. If it is all mineral (no organic matter) and well compacted subsoil, then *possibly* 2 inches of screenings would be just fine.
What is generally recommended is a solid 4 inches or so of well compacted roadbase.
As for the treated lumber…I’m not a fan of using any sort of edging material for around flagstone. Also, treated lumber being laid on the ground like that is going to be exposed to the elements, wand will thus leach out roxins into your yard. Personally, I’m not a big fan of toxins in my yard. And in this case, it can certainly be avoided. I’ve written an article explaining why I do not use plastic, treated wood, or concrete edging material for my flagstone work, here.
OH WAIT A MINUTE…
you’re covering an old concrete patio with dry laid flagstone. Um, I still don’t like it. What you’re doing with the screenings is creating a place for moisture to sit. Sure, the concrete patio that you are building on top of is probably pitched well enough tyo shed water…but then if you use the treated lumber at the edge, then that water is trapped.
Despite my being a huge fan of dry laid flagstone, if you’re going to build on top of concrete, I’d probably just mortar the flagstones down. When I dry lay on top of screenings, there’s gravel beneath the screenings. Water has a way to percolate.
SO if you were going to insist on dry laying, then just use larger stones at the edge. And keep the joints tigh enough that most of the water can shed downhill on top of the patios surface. Better yet, wet lay. Set the flagstones on a bed of mortar.
Whatever you do, do it with heart.
Best of luck with your patio!
Hi Devin, I have an old (20yrs) flagstone patio that is sinking & water going under/into my foundation when there is a heavy rain. I live Battlement mesa, CO. We want to raise it & reset the flagstone. What would be the best base & joint material to use for no water seeping into the foundation and away from our home.. Thank you for your time & professional opinion… Sandy
Concrete is likely to crack, in a northern environment….but a cemented in patio will of course be much less likely to allow water to get to your foundation.
Of course, I like to keep it natural, and eco. I like to use dry laid tactics, creating a patio that can flex with the freeze-thaw cycles.
One way to make a dry laid patio so that little or almost no water gets through would be to simply fit your stones super tight. Perhaps going with dimensional flagstone–squares and rectangles. Do that and also pitch the stones abit harder than you usually would and the water will run off. Say for the first 5 feet or so along the house, you’d pitch the stones so there is plenty of pitch. Usually you’d want a patio to pitch about 2.5 inches over a ten foot span, or 1 inch over a 4 foot span. Same difference, see?
Another method that I’ve used, at the customer’s request, was to bury a sheet of plastic beneath the flagstone. Not my favorite method. We laid gravel, raked it out with proper pitch, tamped it, got it really flat and smooth, then laid plastic. Then we laid the flagstones in stone dust. Water no longer got into the foundation on that side of the building. My only concern with that method is that moisture might then just sit in the stone dust. I visited the site later and if moisture is sitting there, you really can’t tell. Then again, it might be attracting creepy crawlies…maybe salamanders. Salamanders are cool though, who doesn’t love salamanders? Someone with a sensitivity to mold *might* hypothetically feel a bit of an allergic reaction there…but this is very hypothetical. Maybe the water is flowing right off the flagstones, what little makes it down to the plastic might actually flow along the plastic and down into the gravel (sufficiently far away from the house). So it’s probably not too much of a concern–you can probably use the plastic method.
We should go back and measure the moisture underneath that patio, to be sure. Science people, I’m talking science. I see you’re name is Darwin. Science!
Good luck with your flagstone and foundation issues.
We have just completed constructing flagstone path. We used 4 inches gravel, then 2 inches limestone screenings and compacted everything. The flagstone are all different thicknesses, and about half the stones need to be raised up so the path stones are all fairly even and there’s a flat walking surface. I have a little gravel leftover from the project. Is it okay if we mix the leftover gravel with yet to be purchased screenings to go underneath those stones that need to be raised up and then use only screenings for in between the stones? I just don’t want to throw the gravel out if I can use it yet.
Yeah, that sounds fine to me.
https://www.devineescapes.com/wp-content/uploads/2014/03/kohr-2.jpg
what is the flagstone used here?
Thx
The flagstone used for that patio is Varigated Pennsylvania Bluestone.
I am trying to order crusher run but when I asked for it the company called it ‘squeegee’. Is that the same thing or should I keep looking for a company that sells ‘crusher run’?
I’ve came across a lot of names for crusher run…screenings, stone dust, decomposed granite, 8th inch minus, ect. But squeegee? That’s just too silly. Ask them to describe it–or visit the place yourself. What you want is gravel that is sized from 8th inch chips down to flour like dust. Good luck with your patio or walkway, and good luck finding the right gravel and flagstone joint materials 🙂
Thank you! I should be using crusher stone for my base, correct? Our soil is very wet – grass will still be soaking wet after two days of not running sprinklers in that area. We also live in Utah where the ground freezes, so I figured we needed a very strong base. Our plan is to dig 8 inches down to accommodate a 4 inch crusher run base compacted then we are going to do 2 inches of stone dust then our 2 inch flagstone. I’m wondering if it’s a bit overkill? Any advice?
Okay…I’m not certain of the product names in your area. The foundation should be 3/4 inch gravel (or 1″…yes, I’ve seen it sometimes with pieces up to inch and a half. the important part is that it has fines), with the smaller bits, 8th inch chips and fines/dust/powder as well. Around here that’s called road base, item number 4, 2a, modified gravel, ect.
Anyway, your plan sounds about right. What I do is dig down about 7 or 8 inches, tamp the soil, then lay 4-6 inches gravel. (the 3/4″ inch stuff with fines) My goal is to have at least 4 inches, that’s why I say 4-6. If the goal is only 4, you’ll end up with spots that only have 3. Anyway, then I lay out my flagstones and one at a time level them out, raising them up as needed, with a half inch to an inch and a half thick stone dust. I don’t thick I ever go a full two inches thick on the stone dust myself…and if I needed that much to raise an individual stone in order to get it high enough, then I’d probably just lay an inch of gravel first, for that stone, tamp it, and then bring in an inch of stone dust. Reason being is that stone dust is not quite as sturdy as the road base.
Anyway, that’s not overkill, I think you’re on the right track.
Hi Devin,
I am so glad I found your site! We are planning a flagstone walkway from our front door – roughly 500 sqft. We live near Toronto. I have been interviewing contractors – the first quoted for a gravel base, the second cement. You are convincing me more and more that a gravel dry lay is the best way to go, both aesthetically and to prevent cracking in our cold winter/hot summer climate. My question is: We have a large maple whose roots lie above the ground in the path of the future walkway. Would a dry laid walkway be better to navigate the roots? Would a wet laid walkway be absolutely detrimental to the life of the tree? Thank you! Jocelyn
Hi Devin – I live in the Northeast. I have 12″ x 18″ flagstone that I want to use as a walkway to my driveway. I’ve found pictures that have the flagstone or concrete with river stones or those mexican smooth stones in between. I’ve included a couple of sites for you to see what I’m talking about. My question is: Will I be able to mow OR use a snowblower over the stones??? What do you think?
http://ideas.ipassyou.com/walkway-ideas-for-your-backyard-project.html
http://godecorator.xyz/backyard-pavers-ideas/backyard-paver-walkway-ideas/
https://s-media-cache-ak0.pinimg.com/236x/66/fb/2a/66fb2a23b1508f62bb4c43e621e51827.jpg
https://www.pinterest.com/pin/180566266283188761/
Going off the one photo: http://ideas.ipassyou.com/walkway-ideas-for-your-backyard-project.html
I’d say you should have little or no problem, if you built your flagstone walkway like this. So long as you do not overfill the gravel…you’d want the gravel just lower than the flagstone, your flagstone about 1/4″ or an 8th of an inch higher than the gravel.
But the other photos show gravel pathways with flagstones just set every once in awhile–those I am calling gravel paths. Or stepping stone paths, with gravel set between the stepping stones. Paths like them, yeah, the blower will probably pick up some gravel. A lawn mower will likely be fine…okay, decades ago I did work as a lawn guy, and we ran those zero turn mowers, the big ex-mark or lazer z, or whatever they are called…anyway, yes, everyone once in awhile one of those things can pick up a piece of gravel. I saw a window busted because of that once. It’s rare though 🙂
My recommendation then is that you eliminate your lawn, and plant a garden instead. Hire me to build your walkway…and we’ll work out a partial barter–reduced price in exchange for you providing me with green vegies, for life.
Do we have a deal?
Thank you! I love my lawn. I just finished excavating old paver walkway, (steps to sidewalk) widened, added new 6″ base, bedding sand, and installed new pavers with polymeric sand for front walkway. So now, just wanted to change the path from the walkway (12″x12″ that’s sinking and too narrow) to my driveway that I have there now. Thought the flagstone with mexican pebbles would look nice. But, was nervous about the mower and snowblower.
You’re welcome. Good luck with your hardscape, with whatever you decide to go with.
The two hundred year old large sandstone pavers on the verandah needs a filler in between gaps.not grout please i need info what type of filler and recipe mix. I heard of lime and fat sand here in tasmania/ australia.please advise.
I’ll need to see photos before I can advise. Post them here, or email me.
devin@devineescapes.com
Hi, one thing I’ve always wondered about sand-filled (& screenings, in this case) is —
Can’t dirt from mulch-mowing, etc. get on top of the sand, settle in, and start growing weeds, etc? I want the most maintenance-free & easy to sweep stone pathway I can have. I’m in mid-TN. If you sell me on this (which you’re really close….if not all the way ;-), then I’ll go this route instead of mortaring the stones above a concrete base. )
So, my main question is — does sand/screening filled prevent as many weeds from growing at concrete does?
Thank you. You’re nice to post & to answer our questions. You obviously know what you’re doing.
Tracy
Weeds will grow in stone dust, with or without any soil actually getting into the cracks, some weeds will find a way to grow between your flagstones.
Tighter flagstone joints will mean less weeds. Larger joints will tend to collect more mulch and soil than smaller joints will….soil gets on top of the patio, rain comes, and soil washes right over tighter joints, for the most part. Wider joints catch significantly more soil, because soil that washes on over the larger joints gets lodged in easier.
Boiling water will easily kill any weeds that do grow in between your flagstones–no bending over and pulling needed, no toxic weedkiller needed…no need to mix soap+ salt+ vinegar or anything like that (and such home weed killer recipes like that will harm nearby lawn and garden plants as well)–just boil some water.
Good luck with your stone pathway, I hope this helps 🙂
Hi,
I would like to install a flagstone patio but without cement. I had a swimming pool removed and the area was filled with course sand. I have waited 2 years for the sand to settle. I live Canada where the winters are commonly minus 30. What do you suggest? Many thanks.
Myra
I’d suggest having 4-6″ compacted road base AKA “3/4″ minus”
gravel for your foundation, stone dust as your leveling agent and get that sand out of there. There’s more how-to articles on this website. Spend some time reading them…if you’re planning on building the flagstone patio yourself and feel you could still use more guidance, then it usually takes me about an hour to walk someone through the whole process: https://www.devineescapes.com/phone-consultations
I stumbled across your article while looking for different types of Polymetric Sand, thank you for your in depth information! However, now I am second guessing my decision… I have natural sandstone that I am using in a 6×9 pathway and some of the joints can get up to 4″. Would you recommend screenings for that application also?
Yes, I certainly recommend stone dust rather than polymeric sand in your situation. Now, 4″ is a bit wide for a dry laid flagstone joint…if the area is steep and or prone to rain, then stone dust joints like that can wash out sometimes, but will tend to stabilize eventually. Might need to be topped off a few times. Planting a ground cover is usually a good option for such large flagstone joints–or just allowing/encouraging whatever wild plants (“weeds”) happen to pop up there. Either one will stop the stone dust from washing out. Polysand will likely just crack and get ugly and let weeds grow anyway.
I built a 15×30 foot stone patio several years ago. I spent so much time getting all of my joints perfect but unfortunately I have been having trouble keeping the stones flush/level. I tamped the ground and then used varying thickness of road gravel as my base anywhere from 3-10 inches due to using some really thick stone. I live in NY which doesn’t help because of the frost. I just spent today fixing a 5×5 area where it sunk in 2-3 inches. My gaps are mainly right around an inch give or take a half inch. I used the same gravel to fill the joints as I did my base but it gets messy with lots of traffic. Would mason sand be alright to use or would I be better off with something else for the gaps. I’ve already let some grass start to grow in and it held up much better in those spots so I was tempted to let the grass take over.
Also I feel my biggest issue is location. My patio over looks a large stream out back where there is an upper and lower bank. Two of the edges of my patio (one 30 feet long the other 15) sit on top of a stone wall I built (3-4.5 feet tall) ants, snakes, and water make it a battle to keep the gravel from sliding from under the patio out the wall. What would you recommend I use to prevent this? I’ve tried wedging stones but to no avail and wasn’t sure I would like the look of concrete to fill the gaps.
It sounds like you did the foundation a bit differently then I would have. Mason sand is not the best option for the joints, as it will wash away. Stone dust is the way to go then.
I’ve built a few dry dry laid patios with dry laid walls to support them…but I build dry stone walls all the time and go to extra measures to ensure there are no voids in my walls, if they are supporting a dry laid patio. Site conditions, such as ants and snakes and water, as you say, may be complicating the issue even further, in your case. More than that I really can’t say, without seeing the wall and patio.
Not sure if I’ve offered you anything helpful, but I wish you luck with your patio and walls!
Hi Devin:
Great informative blog! We have a hand cut, ground level flagstone patio under an existing second story wood deck. The flagstone was laid on limestone screenings and polymeric sand was used for the joints. Looked lovely until it rained! The rain drips from the above deck into the joints and splashes polymeric sand all over our patio doors. I am now looking at adding black granite screenings to the joints? Question: Do I have to remove all the polymeric sand first or can I go down about 1″ and then fill in with the screenings. We hope this works! We are in Muskoka, Canada. Thanks for your help!!
I would recommend removing all of the polymeric sand. Small voids exist underneath some of the flagstones… having stone dust for the joint material means that if a new void forms beneath the Flagstone, then the stone dust from The Joint can wash down and settle down into that void. If you leave some polymeric sand down there, it could serve like a barrier stopping the stone dust from sinking down in there if it needs to. This could cause individual flagstones to settle and sink or develop a wobble.
HI Devin: Great article and interesting/useful information in the questions and answers. I live in central OK and am doing a DIY flagstone patio (18X20 feet). It abuts the house on 2 sides. Don’t have a lot of elevation to deal with and the soil seems fairly solid. I’ve already build a cut stone (3.5X6Xvarious, HXWXL) low wall for outside edge. My question was what is the minimum depth of gravel and then screenings work OK for a 1.5 inch irregular flagstone pavers (hope 1.5 inch is thick enough for normal foot/furniture usage). Really like you screenings suggestion.
1.5 inch is generally thick enough for dry laid flagstone, unless the stones are less than a square foot or so in size–if the stone is both thin, AND has a small amount of surface area, then it may wobble a bit undrerfoot. Anyway, I’d say you’re fine there.
Minimum gravel and screenings….is a tricky question. A site-specific question. I do not know how stable your soil is. But I do know OK has less of a freeze-thaw issue than the areas where I usually work. Around my area I’d say to use 4-6″ of gravel. 4″ is fine. 6″ is overkill–but I usually recommend 6″ because if you tell someone to use 4″, then they are going to have some thin areas where it’s more like 3″. Telling them 6″ covers for mistakes, and is a bit of overkill that helps ensure success. the real answer, for most areas I work within, is 4″–but in a situation like yours–where the existing soil is quite stable, and you have site conditions limiting your elevation then okay, 3″ is fine.
But there’s some things I do not know–your soil is “stable”. How stable? Is the soil gravelly? What are the percentages of gravel, sand, silt, clay and organic matter? If you have a lot of gravel if your soil, a bit of sand and silt and some clay, but basically zero organic matter then, I mean, it’s possible your soil is already a good base for flagstone. The worst thing to build upon is organic soil. The best, is gravelly soil.
You could do a jar test:
goo.gl/fn2UbZ
A truly stable soil will be mostly gravel and sand–and will have been undisturbed for over 5 years. No one will have dug, the soil will have sat, and will be well compacted into itself. I hope that helps. 3 inches? 2 inches? 4? I do not know. If you took a jar test and sent me the results, and emailed me photos of the jobsite along with measurements for the existing elevations, and amount of yearly rainfall, then I could determine what you need for your foundation and just give you a simple number and other site specific recommendations. If you need all that, then we’d want to set up an email consultation.
Otherwise, good luck!
Morning Devin,
I’ve been reading up on everything on your blog and trying to figure out what would work best for a flagstone walkway we laid in the back of our house. We removed an old flagstone walkway as the joints were cracking and we changed the layout a bit, but we’ve relaid a flagstone walkway. The only difference this time is we installed stepables in-between the stone with soil instead of polymeric sand.
Our base is 3″ or so of manufactured sand as our base, but we are having wash out problems on our slope. We installed a drain at the top of the slop to capture some of the water before it ever gets to the sloped area which has helped but now the washout has moved down the slope but still exists. Have you ever put a drain under a flagstone walkway to capture water and get it away from the walkway or would there be a better way to approach the drainage? I’m also thinking if we excavate more and be sure there is more soil on top of the base it would hold more water and slow the flow down as right now the soil is only in-between the stones and the stones sit directly on our base material. Thanks
Clever grading should be able to fix this issue. I’ve never installed such a drain and have never built a flagstone walkway that required a drain. The walkway needs to be pitched right, to take away surface water, and the areas surrounding the walkway need to be pitched right. Possibly your walkway will need to be raised in elevation in order to conquer this issue. That’s about all I can offer, without studying photos and without access to elevation measurements. I wish you luck and I bet you can handle this yourself…but of you’re really stumped and need further guidance then I will need photos and can instruct you on what I need by way of elevation measurements. But hey, maybe I’m mistaken and a drain is the right solution. Can’t say for sure, without more info to go on.
Devin,
What is the best kind of stone to use under the flagstone (Crusher?). The last people that lived in this house had flagstone set on sand in some areas and top soil in other areas. The ones with sand shifted and would sink. We saw increase in ants during the spring as also ground bees at the beginning of spring. Also is there a big difference between stone dust and pea gravel for finishing?
I recommend using 3/4″ gravel with fines for flagstone patio foundations, then stone dust for the leveling agent. This 3/4″ gravel with fines is just 3″4″ gravel, with stone dust mixed in. Pea gravel, if used as the joint material between your flagstones, will not tend to stay in place, will get all over and generally be a mess. Stone dust, will consist of 8th inch chips of stone, then small bits, all the way down to fine stone dust, like flour. This stone flour, when dampened, binds up a bit, helping to keep the flagstone joint material in place. Also, read this article about flagstone joint material.
Great advice! I am about to put in a flagstone patio. I am not sure if I will use irregular or square cut stone. I am concerned about 2 things. What is the best way to lay it for drainage. I was thinking wider gaps filled with the stone dust would allow drainage. I am also concerned about shoveling snow on the part of the patio which will be a walkway from my garage to the house. I don’t want the edge of the shovel running into the edges of the stone too much. I understand that proper installation and leveling is key, but am concerned that gaps that will allow drainage will also be an obstacle for the snow shovel. Appreciate your comments.
Sure, with wider gaps water can settle down into the ground a bit faster, but not by all that much. The difference between a 3 inch gap and a half inch gap between your flagstones is usually not all that great, as far as storm water draining away goes. To handle storm water, I set my flagstones at a pitch of about 2.5″ fall over 10′ of span. This is the same as saying 1″ of fall over 4′. So as I’m leveling out my stones I can use a four foot level and know that the bubble should center itself neatly, if I lift the level up one inch. In practice, the way that it works is I set up string lines, and get my gravel foundation set at about 2.5″ fall for ever 10′. This number is approximate–for some projects it may be more like 2 inches, or 3. Less than 2 and water might not flow off the patio fast enough, might leave a bit a puddle that takes some time to settle. If you make the patio much steeper than 3 inches, it could potentially feel like you are on a slant, rather than feeling level.
Yes, wider gaps may make shoveling snow a bit more difficult. This would probably cause you to end up removing less snow, leaving some down upon the flagstones, so tighter joints are preferable then, in that regard.
I am in the process of planning a 5’x11′ walkway to my front door. I have a variety of slate in blues, grays and reds. The slate is various sizes and shapes; some rectangular and some with an irregular shape. I would like to set the pieces in cement to avoid the problem of weeds growing in between the stones like in the past (the walkway originally had stone dust in the joints). However, I do not like the light gray-white color of the cement. Can I sprinkle a layer of stone dust into the cement to create the illusion of stone dust joints? Thank you for your advise!
No, not really…Sorry, I just don’t know of any effective way to create the illusion of having stone dust for your flagstone joints. Good luck though, whatever you go with–and I hope you find my How To articles helpful.
Hi Devin,
Thank you for all your input and advice! 🙏 My partner and i are novices and have taken to doing stepping stone courtyard thats approx 80 sqm 😲. We are in Australia in qld. We have pretty hard compacted clay soil and one end was mostly dirt (where grass once was) and a grassy prickle infested area at the other. Area tends to stay “damp” (though not soft) when rains (not that it does much) and during winter. We have now covered the entire area in crusher dust (one level thinner than road base). There is a slight grade towards the house and one end needed more fill to level it out (about 6in one end to 3in the other – the grassy end.) We have a combination of rectangle pavers for the outer edges and crazy pave for the inner. I intend to plant out between the pavers with wild thyme.
So to my question…do we mortar under each stone or just lay straight onto the crusher dust? And if the latter how do i stabilise each paver if I’m wanting to put soil between each? There’s not much play in height (to the top height of a retaining sleeper that runs the length on one side) at the thinner end.
Hope the makes sense and happy to rmail pic of area and what im hoping to acheive if that helps.
Namaste Shana
No mortar. You should re-read the article, and then read the rest of my how-to articles. Never, ever (x 10,000) use mortar underneath a flagstone unless you are building on top of a concrete foundation. To stabilize your flagstone a) make sure your flagstone is of an appropriate size. A small thin stone will wobble. b) get your stone dust right. c) set the flagstone in place with a mallet.
When I finish laying a flagstone patio, it’s usually about 85 percent wobble free. Then I sweep in the stone dust between the joints, hose it all down and repeat, multiple times. After that, I’ll check the whole patio for wobbly stones, and use the mallet to correct any that I find, lifting up stones and placing more stone dust beneath them as needed, malleting them down, sweeping in stone dust and hosing down again. At the very end, the patio may be like 98% wobble free. The flagstones feel rather stable. If you walk around, you may notice a minor wobble underfoot…if you used stone dust as both your leveling agent, and as you joint material, this small amount of minor wobbles will correct themselves over time. I’ve never once noticed any wobble, on any of my dry stone patios and flagstone walkways, when I return months, or years later–so minor wobble will definitely correct themselves. Mind you, I spent a lot of time working to get everything 98% wobble-free, before calling the job finished.
EDIT Okay, I see now that you want to use soil between your flagstone joints. No problem, just mix that soil with stone dust….I’d recommend at least 1 part stone dust to 1 part soil–and probably heavier on the dust dust, more like 2 to 1 or ever 3 to 1.
Good luck!
Devin, thanks a lot for all this information. We live in Northern Virginia (suburbs of DC), and we are planning to get our patio done with Flag stone. We were really confused between mortar or dry set, but your article helped us a lot in making our decision of going with dry set.
I just have a quick question for you – have you heard of weed problems with dry set, is it difficult to keep them out/ take them out without taking out the poly sand?
Basically all the contractors here are telling us not to go with dry set. They are saying that there will be lot of weed problem and we have to regularly maintain it.
We will really appreciate any advise you can give us.
Thanks!
Your local contractors are mistaken.
With Dry set, you get a weed, just pour some boiling water on it.
That’s with real dry-set–which involves zero polysand. Polysand will crack and weeds will get in there and now fixing it is a major problem. Here’s an article where I go into a little bit of detail about some of the failures that polymeric sand causes.
The thing about dry laid is it takes a lot more skill. You have to fit the stones tighter, because you are filling the joint with stone dust, rather than cement or plasticy-sand. You have to pay attention when leveling out the stones, because you are not just squishing them down into wet mortar. As such, most contractors just don’t know how to do dry laid. I know this because contractors call me almost as often as homeowners do, for phone consultations.
I do travel for work, sometimes. Did a job in Silver Spring MD last year. Email me some photos and measurements–sometimes it works out where you can hire me, an actual specialist in all things flagstone, and even including my accommodations the price is still comparable with your locals.
11 years in business–not a single patio of mine has ever had a significant maintenance problem. That’s why I never ever install a new job in mortar–unless I’m laying it on top of an already existing concrete foundation, then sometimes it is better just to wet-lay. And of course I also do some repair jobs–repairing wet-laid patios that other guys build.
best of luck!
Hi!
Really enjoying your insight on flagstone! My husband and I laid a goregous firepit patio last year. We dug out the area used pebbles, then screening and leveled our flagstone in the used Gator Dust on top🤦🏻♀️. A year later in New Jersey after a horrible winter the Gator Dust is either cracked or gone! The staff at the Rock Yard we purchased the flagstone from recommended the Gator Dust, and we listened 🤦🏻♀️ . You can see the screening in between the stones in the places the Gator Dust washed away. We want to fix the patio, hopefully without digging up the flagstone and starting over. Can you offer any suggestions?
There’s too much here that I don’t know. If the foundation is in decent shape, then you can simply remove the gator dust and replace with real stone dust. First, you’re going to have to get down and use a screw driver, pocket knife, or something, to dig out the old polymeric sand from in-between the flagstones. Then just sweep stone dust in between the flagstones, hose down, then repeat a couple times because every time you hose down, the stone dust will sink, will find voids down there and fill them.
But you said the foundation is “pebbles”. What do you mean by pebbles–pea gravel, river rock, what? Are the pebbles jagged, or rounded? Is it just pebbles of one size, like 3/4″ or 1″ pieces–or is there small chips of stone and fines mixed in? How deep is the foundation? Did you tamp the subgrade? Did you tamp the gravel?
In New Jersey, Pennsylvania and the region, you want a good 4-6 inches of foundation…usually. I’ve seen people get away with building just on clay soil though–as a professional, I can’t take chances like that, neither can I advice homeowners to work with zero foundation BUT, if you’ve already done something unconventional, it’s not a certainty that it will fail. My concern about pebbles is the voids in between the pebbles–chances are, if you have 3 inches of uncompacted pea-gravel (which is what I’m assuming at this point) then over the years there will be some settling of the flagstones. The surface may still be walkable, just not nice and flat, you may or may not need to re-level the stones once or more, throughout the lifetime of the patio. Also, if the foundation is like I think it is, then you’ll likely need to top off the stone dust in the joints more often then you would otherwise, like a few times in the first few years, until all the voids down way beneath the flagstones are filled.
I hope that helps!
Hi Devin, great reading all your articles. We live in MD and have a flagstone patio, that has been done twice. The first time we used grass between joints which worked for awhile, it was beautiful! But our trees grew over the years and most of the grass had too much shade and the grass died. We had some guys redo it, they reset the flagstones but they still left the joints almost 3 to 4 inches part, to save on flagstones and used some type of filler that hardened, that worked for awhile, but not long. They were inexperienced workers and we were told they did not install the filler properly in the joints so it failed, cracked and now most of it is coming out or already has. Question, the flagstone is still in tight, they don’t move underfoot happily they did that well,the patio drains well, etc., we don’t want to redo the whole thing. I just don’t know what to put in those wide joints to make it work because they are so wide. Would stone dust work mixed with pebbles, just a lot of stone dust, or should I bag that and try moss or some type of vegetation in the joints. The idea of doing vegetation also makes me hesitate because I will need to put in a little soil and if it fails, doesn’t grow well, dies, it will be a pain to fix the joints again. It’s a pretty nice sized patio so anything will take some work and we really can’t afford someone to do a redo. Help!!
Use stone dust. Since you liked it with grass in-between the flagstones, and now there’s too much shade for grass, the first idea that comes to my mind is moss. This will give you a stable flagstone joint, with a similar look to the grass. Also, you needn’t mix any soil into the stone dust, as moss will grow directly on the stone dust. I would recommend buying some 1/4″ minus quarry fines, filling in the joints with that. Then, find some moss already growing on your property, if there is any. Mix up the moss in a blender with butter milk, stale beer, or even just water. Pour that slurry into the spaces between your flagstones. Will need to be watered on occasion, until it takes. I like to plant a couple clods of whole, living moss, as well, here and there–and then do the slurry method for the rest of the patio.
This method may take awhile. In the meantime 4 inch wide joints are generally considered too wide for flagstone joints that are filled with stone dust BUT I have seen people get away with it. It’s not guaranteed to fail…but rather, if trying this method you just will likely have to top off the joints a few times, over the first couple of years, while waiting for the joints to stabilize themselves and/or for the moss to take hold and stabilize that stone dust for you.
Hope that helps–good luck!
Devin. Your advice and detailed responses are fantastic. My question is about the maintenance of the s screenings between the flagstones. How do I keep the tiny gravel bits from releasing every time I sweep, wash or leaf blow the patio? Do they eventually release the loose ones and stay stable? Can I add some polymer sand filler to hold them in place?
Thanks,
Doug
Don’t overfill the joints with screenings/stone dust. You want your screenings to be a bit shy of the top of the flagstone–if the stone dust comes up even with the top of the flagstones, then the stone dust will easily kick out and spill all over the place. Sweep your stone dust into the joints, then hose down, on shower setting. You can use the hose to wash out excess stone dust.
https://www.devineescapes.com/how-to-clean-dry-laid-flagstone/%
Just say NO (thank you) to polymeric sand:
https://www.devineescapes.com/polymeric-sand-is-often-recommended-for-filling-in-the-joints-between-patio-stones-i-do-not-recommend-this-practice-and-i-will-tell-you-why/%
Devin, I’m so glad to have found your site before starting my project. Definitely going to be going with breeze under and in between my flagstone despite everyone pushing Polymeric sand!
My question concerns spacing. I’m going to be using dimensional cut red sandstone flagstone. I’d like to get them as tight as possible to avoid issues with patio furniture. How tight is too tight? 1/4 too close? I live in Colorado, so freeze-thaw is a concern. I’m also potentially concerned about drainage as the area is flat. The patio will be 450 sq ft. The back of the house is, if anything, actually 2″ lower than the alley-facing garage 30 ft. away. While the previously-laid brick didn’t have drainage issues (other than low spots where it’d sunk), I’m afraid of this project creating an issue. How would that affect my gaps?
Also, how would that affect my depth of sub material? Since it’s a 130 y.o. house with well-compacted soil, the stone sellers suggested just going with an inch of sand for leveling and not worrying about putting a layer of road base underneath. Would you change that recommendation based upon it being flat? Does breeze and/or road base drain better than soil?
1/4 inch gap is fine. Dimensional flagstone is usually cut to nominal size–a 24″ flagstone will actually be 23 5/8″, give or take an 8th of an inch. As such, you’ll end up with gaps between your stones of 1/8″ to 1/2″, and that’s fine.
With your freeze-thaw cycle….as a professional I would certainly still go with a road-base foundation. In fact though, if the soil is 130 years undisturbed then sure, you could most likely get away with simply removing the top soil, sod, anything organic, and then compacting the sub-soil and laying down breeze. You could lay an inch or so of breeze, then lightly dampen that, ramp it, then lay out all of your flagstones, then use loose (not tamped) breeze to level up each individual stone.
You want the water to drain though. I don’t want your new patio to have adverse effect on your homes foundation. Ideally, you’d direct the water flow away from the house with about 2.5″ inches of fall for every ten feet of patio. If that is not possible, then direct the water along the length of the house. You can pitch it a little bit harder, more like 3″ fall for 10′, or even 3.5″, and it will still feel level.
Before trying that however, I’d first try and find a way to pitch the water directly away from the house. Perhaps a small retaining wall, even 6″ high curbing or something, along the alley.
Hopefully that makes sense and is enough to get you going. If not, you can email me @ devin@devineescapes.com, and send me payment via paypal to set up a phone consultation, during which time I can review photos, describe how I would handle the grading challenge.
And yes, stone dust and/or road base will drain faster than clay soil. If your soil is topsoil, then that may drain fast–but again, you don’t want to build on top of organic top soil.
Hey Devin,
Great site you have – thanks so much for having it up. When making a flagstone path on a slope is there a limit of steepness that you generally follow that you will step the path rather than keep it smooth? I ask because the path I’m going to put in will be functional as well as aesthetic (wheelbarrow/lawnmower/etc) rolling on it. It will be on a slope, and I would like to keep the path “stepless” if possible, but don’t want the stones to slip. I guess I’m looking for a number, like “don’t go past a 10% grade” or something like that. What do you think?
Brian,
I don’t have a hard and fast rule….I’ve gone as steep as 20%. But that was with thick sturdy flagstones. If you go much steeper than a 5% grade then you can expect stone dust to wash out of the joints. Depending how steep it actually is, how much rain and surface run-off the area is exposed to, you might–or might not eventually get the stone dust to stay in place, after filling it and re-filling/spot filling as needed, over years.
Dimensional flagstone with square pieces of stone fit snug might be a good option in such a scenario. Or, perhaps irregular flagstone with grass planted in-between them. So at this point, I really can’t say what is best for your project, aesthetically and functionally–hopefully I’ve still been helpful. If you want to set up a phone/email consultation, send me some photos and we can design something specific for your site.
…or maybe consider shallow steps, that you can get a wheelbarrow (but maybe not the mower) over easily.
Devin I’m right down the road from you in Media PA, I was going to do an irregular stone patio and I’m concerned I wont be able to get my joints really tight so I was thinking of doing grass or clovers in the joints. Any suggestions what would grow well here in PA and not overgrow the stone itself ? Thanks
Sorry–I thought I’d already responded to this. Creeping thyme, ajuga, moss, grass–depends on the look your prefer. Also on the sun exposure. Myself, I’ve mostly only worked with grass and moss, for living material within stone patio joints. Moss if it’s shady, grass if it’s sunny. Sometimes, I’ve planted moss, grass or ajuga taken from the same property–if there was something growing there, or near to there, before you put a patio there, the you already know it does well on your property, with it’s conditions.
Be aware that whatever you use it will likely require some attention, to get it rooted and doing well.
There’s a website called steppables https://www.stepables.com/ if you’re looking for something that doesn’t already grow there.
Good luck!
Hi Devin,
In the Milwaukee area I have not been able to find granite dust, stone dust, etc that is 1/8” minus in size. The closest I have come is 3/8” minus after calling all the local suppliers. I’m concerned it will be too large. The gaps between the stones in my project are about 1.5 inch for the most part. Using 1.5 to 2 inch thick flagstone. What is your recommendation? Go with the 3/8 inch minus, or resort back to a sand?
3/8th minus should be alright–and a much better pick than sand. First of all, don’t overfill the joints. Ultimately, joints should be about a quarter inch below the tops of the stones. If the joints are filled all the way to the top, they will tend to kick out and be all over the place.
I hired a guy to do concrete work from a new paper ad and now as he is doing the work i am not sure about the quality. I asked for his license and just checked the number and it shows expired earlier in the year. It’s a small one car driveway and he is supposed to set quartzite flagstone on the front porch. However, my neighbor just mentioned permits and when I asked my contractor he said we don’t need one. Also the area where concrete needs to be pored is very uneven and the rebars are super skinny. the ground is not leveled and neither does it looked well compacted. There are huge chucks of my old drive buried in this thin layer where he expects to pour concrete for the driveway and set pavers over concrete on the front porch. Any recommendations?
At this point no recommendations…. check references, look at online reviews, and definitely look to see a portfolio of similar projects completed– before hiring.
However most of what you have to say doesn’t really sound all that alarming to me. For example I’ve seen concrete guys pour concrete on top of loose gravel, that is all 3/4 inch chunks of gravel without any small bits filling the voids, meaning it is what we call clean gravel, which is not really compactable. I mean, what you describe is not really the exact way that I would generally go about pouring concrete, but based on what you are telling me alone I cannot say whether or not this guy is doing huge mistakes that are going to cause a problem. I really can’t say. The most I can say is good luck, and sorry, but I don’t really have anything too helpful to say here.
Hi Devin,
I am working on resetting my flagstone patio in Pennsylvania and I am worried about what mortar to use due to the joints being so large. In some places the joints are as large as 5-6 inches. I was planning on using a standard mortar with lime for laying stone patios. Do you think the large joint areas will shrink and crack while it is drying or will I be okay as long as I fill the joints fully?
Gary
5 to 6 inches is considered too wide for a mortar joint. Either fit the stones tighter….or cross your fingers, I guess, but I can’t recommend going forward with joints that wide. Having said that, I’ve seen flagstone patios with wide joints like that–that did manage to last years without problem. As a professional, I can’t gamble like that and I would urge you to make adjustments in order to shrink those joints a bit. Also remember that if you are using mortar for the joints, then the foundation has to be concrete. If the flagstone are laid dry, the joints have to be dry. Good luck and I hope that helps!
Hi Devin,
I admire your work from afar, here in Southern California. I spoke with a contractor today about laying a flagstone patio in my backyard. Instead of decomposed granite he suggested using a drought tolerant ground cover. I am not sure if this would be durable. He did say the irrigation they’d install would keep the ground cover from dying. What are your thoughts on ground cover vs DG between in the joints?
Ground cover usually takes some time and attention to get it going. Once it’s established, it can be quite durable. I’m not too familiar with drought tolerant ground covers in southern california though…
Personally I usually go with stone dust/DG in the joints. If a customer wants to go with a ground cover, then I inform them that the ground cover will need to be watered regularly while getting established, and possibly re-seeded/new plugs planted, maybe once within the first year.
No irrigation needed if you go with stone dust. I prefer to keep it simple. Ground cover is not too complicated, fussy or much of a maintenance issue–provided you’re into it, provided you love the ground cover and it’s something you actively want. I’d recommend you see an example in person. Somewhere in Southern California there’s a flagstone patio or walkway built using the particular ground cover your contractor is suggesting. Compare that look to DG joints and there you go.
We are putting in a flagstone floor in our Earthship type home. Since it is inside is it better to place the stone on cement base or just sand? I have to grout for code and seal. I was thinking about boiled linseed oil to seal and turn the flagstone into a rich, deeper color.
Any advice welcome, never did this before.
Thank you
Well if you’re building an earthship, let’s be as eco as possible and try and avoid the cement, if we can. But I’d need to know more–where is this being built, what is the climate like there? Is it going to be a rubble trench foundation, CMU, or what?
As far as sand goes, I have to advise that ants love river sand/play sand/concrete sand. If you’re able to go dry lay, then I would use stone dust/quarter inch minus/decomposed granite/whatever they call quarry fines in your area.
IF you use grout for the joints, then your joints will be rigid–as such, you don’t want movement under your flagstones, you want a rigid foundation. For outside work, you never want a rigid joint on a flexible foundation–so dry lay on stone dust with grouted joints is a no-no. But if your working inside…..and your area doesn’t get below freezing….and it’s an earthship, so we’re trying to keep carbon footprint low……then, in your case, you might get away with dry lay and grouted joints.
If you do that, then you’ll want to pay special attention to compaction. Dig down to mineral soil, clay or stone. Compact. Lay gravel, compact again. Lay out flagstones, all of them. Fit them tight–no giant gaps. Level up the stones one at a time, using stone dust as your leveling agent. Fill joints with grout. Better yet–fill joints with a cob mix (minus the straw), tooling the same way you would grout. Let that dry, linseed oil both the stone and the joint.
I hope that helps!
Good luck 🙂 Building your own home is an awesome thing. Live it up!
Devin, Thank you for taking time to consider my question. I have an existing small concrete patio. I’d like to make a flagstone patio that covers the existing concrete and extends significantly beyond it too. Can I successfully cover my existing concrete patio with flagstone AND also extend the flagstone beyond the existing patio over a base as you have described above? Or, should I jack hammer the patio out and put the entire flagstone patio over a new consistent base. Thank you!
Short answer: Yes.
Basically, what you’re doing is butting a dry stone patio up against a wet laid patio. Or building a large dry laid patio, with a small wet laid section in the middle of it. No problem there, so long as each part is done well. Take your time, fit them stones well, do not expect it to go super fast. Unless your laying dimensional flagstone.
Another option would be to extend the concrete foundation. To do this, you’d drill into the existing concrete and epoxy in some rebar, sticking out of the old concrete, and tying into the new. I’d paint the old concrete with bonding agent/concrete fortifier too. This option probably doesn’t make sense, because you said the new patio will extend significantly beyond the old. But how much is significant? If it was 100 sq ft patio that you wanted to extend by 30 square feet…I might consider just extending the concrete foundation. But if you were adding another 100 sq ft, then I’d just build a dry laid patio next to the cemented in one.
I am in a similar situation as Jay, wanting to expand and cover my existing patio. Just clarifying, is it fine to dry lay the stone over the existing concrete, or preferable to use mortar in this situation? Was thinking I could make the gravel base level with the concrete patio, then overlay both the concrete and gravel base with stone dust to set the stones in. I also want to cover my existing concrete walkway. is it ok to dry lay stones over that as well? Thanks for your wonderful blog!
Yes.
In fact, there’s many ways to handle a situation like this–but if a customer brings me a small concrete patio and then tells me they want to replace it with a larger, dry laid stone patio, my first option would almost always be to overlay the concrete patio with flagstone set in stone dust, and have the new section of patio built on well compacted 3/4″ road base gravel–so long as there’s enough room to raise the patio up enough to accommodate flagstone and stone dust, maybe 1″ dust, 1.5″ to 2.5″ flagstone.
I need to email Jay, may have given him less clear advice/seems I misunderstood his question.
Hi Devine, I m in east coast. So I have the typical thaw freeze cycle in winter. I have both concrete and dry flagstone in my yard. I paid someone to do a small concrete patio next to my side door when I bought my house. The patio cracked within 2 years. It was done horribly. Then to save money, I paid someone to install the 80 feets long dry flagstone path on gravel in the backyard. They filled it with polymeric sand. But it was also done horribly since the polymeric sand is breaking apart so often. All the weeds are growing in between the joint. It’s a lot of work for me because I have to constantly unweeding and filling the joint with more polymeric sands. I experimented a small patio by filling the joint with Mexican pebbles one by one with polymeric sand to stabilize the polymeric sand from being washed out. It’s much better with the Mexican pebbles to fill the joint. However, I m going to fix the 80″ long path in my backyard. I know you mentioned it’s a very bad idea to use cement to fill the joint between flagstone. I m wondering will it make any difference if I fill the joint with pebble and cement together to stabilize the movement. I have this idea because I have been reading books about pebbles mosaic. Some pebble mosaic patios are built directly on excavated area without concrete based. By selecting the tightly fit pebbles to fill the joint, will it minimize the stone movement to avoid cement cracks? I am in search for a better way to repair the flagstone path for better durability. One major problem is my flagstone path is slightly sloping down, so I have lots of water running on the path when it rains.
I think that’s also the reason, the stone dust can not hold in place. They are being walked out between the joint. Thank you in advance for your professional opinions.
Pebbles and cement will be a rigid joint, on a flexible foundation, between stones which may have minor movement. I predict you will have a situation similar to the polymeric sand–continuous maintenance and weeds. I’d suggest you fit the flagstones tight enough that they don’t need joint material or you leave the joints large and fill then with larger pebbles with no binder. Dry laid pebble mosaics are one thing, but a cemented-in pebble mosaic element in the middle of a dry-laid hardscape….it give me concern. This is my opinion. Good luck, whatever you end up doing!
I have one more question. I saw a new product called gravel lock which is used to lock the gravel in place like a path. Will it works to be strong enough to lock the gravel in place for the joint between flagstones? My flagstone path has solid edging with mortar in place. I m willing to explore any new products and ideas. Thank you so much.
You asked for my opinion.
I’m not very much into new products. New ideas, sure. Most new products are just plastic ways to cheat, don’t last long, aren’t natural, probably off-as voc’s, never are eco (even if they claim to be). Ticky-tacky. Gravel-lok, polymeric sand and similar products are ticky-tacky. Why should plastic be a landscape product? Landscapes are made from soil and stone and life–not plastic. What I am discussing in this blog, and what I do for my career–is natural stone work, time-honored, traditional craftsmanship, and it does not rely on space-age products, or gimmicks (such as polymeric sand–how did that work for you?).
Hey–maybe gravel-lok is just what you need. Take your time, make it work…..but IDK, I never used the stuff and I always prefer to fit my stones right, resorting to modern products only as a last resort. Good luck to you, whatever path you take.
a landscaper is installing a 2’x3′ flagstone walk and patio for us. They are laying 2″ of fine crusher run tamped with a hand tamper. The flagstone is mostly 7/8-1″ thick with some 3/4″ and 1 1/4″. Can we get away with this or should the crusher run be thicker or should there be a coarser base beneath the fine considering how thin the flagstone is? thanks.
I’ve had to field questions like this before….and it’s really not what my blog is about. I don’t want to be the guy who, you hire some other contractor–and then after agreeing and signing papers you decide to question their methods–so you find me. I don’t like being placed in the middle. DO you see how that’s an awkward position that I’m unwilling to be placed into? Having said that, I won’t say that what this guy is doing is wrong, but it sure is not the way I’d go about it, at all. Pay me for my time and provide some more info and then I can provide my best recommendation of how I would do this job. https://www.devineescapes.com/phone-consultation-professional-hardscape-help/ Best of luck, email me if you want to do a consult!
Hi Devin I have a bluestone walkway in CT. it is set on cement. we need to replace the bluestone and we’ll be going with 24 x 36 inch . we’d like to have grass in between the stones. as the path ins now below the level of the grass bordering it i was thinking of pulling up the pavers and putting stone dust directly on the cement maybe 2″ and cutting out the cement where the grass will be.
thought ?
It is possible to dry lay flagstones on top of a pre existing concrete slab. Make sure the slab is pitched/ not perfectly level, and make sure to set your stones pitched as well. Direct rain water where you want it to go. Also keep the joints toght enough so that a ton of water can’t get down under them flagstones, potentially trapping moisture in the stone dust, which can’t really deain through the concrete.
Having said that–in all my years doing hardscapes, I’ve never seen that problem arise–trapping moisture in the stone dust, bound by the preexisting slab. Still, I’d keep the stones 2 inches apart, or closer.
I’d prefer to set the flagstones in approximately 1″ stone dust. I hope that helps!
Thank you for this informative write-up. I used local screenings instead of poly-sand to redo the joints on my flagstone patio and am very happy with the results.
My only suggestion is to add a note in your post recommending the use of construction mask when applying the screenings. I did not realize how much dust I must have been breathing in until I stopped at the end of the day and had a dry cough and pressure in my chest. I will be wearing a mask next time!
You’re welcome–and thank you for the suggestion. Wow! I never thought about that before. I always buy screenings in bulk, by the truckload, and it’s stored outside/gets rained on, so there’s usually not too much dust. Perhaps during the hottest and driest months of the year it might become a dusty situation, spreading stone screenings around…..especially if you live in a more arid place.
Personally, I always have a bandana around my neck, ready to get pulled up to cover my mouth, whenever I’m doing any stone work. I do this because dusty situations always happen on my jobsites. Someone may be cutting a stone with a saw or grinder, sometimes trimming stone with hammer and chisel makes dust, sometimes concrete may be being mixed…and now that you mention it yes, spreading out stone screeings, sand, or any soil type, may create a dusty environment.
Hey Devin,
Enjoyed reading through your blog. Helped me make my decision on finishing a flagstone patio. While reading through your blog I copied bits and pieces and decided to share “your responses” w/your readers. Hopefully they will zero in on these notes thereby not having to ask the same questions over and over again thereby freeing you up to go work on that next patio! Cheers from Austin TX
Dry Laid Flagstone Patio
What I do is dig down about 7 or 8 inches, tamp the soil, then lay 4 to 6 inches compacted road base (the 3/4″ inch stuff with fines). My goal is to have at least 4 inches, that’s why I say 4-6. If the goal is only 4, you’ll end up with spots that only have 3. I then lay out my flagstones and one at a time level them out, raising them up as needed, with a half inch to an inch and a half thick stone dust. Stone dust will consist of 8th inch chips of stone, then small bits, all the way down to fine stone dust, like flour. This stone flour, when dampened, binds up a bit, helping to keep the flagstone joint material in place. I don’t ever go a full two inches thick on the stone dust myself…and if I needed that much to raise an individual stone in order to get it high enough, then I’d probably just lay an inch of gravel first, for that stone, tamp it, and then bring in an inch of stone dust. Reason being is that stone dust is not quite as sturdy as the road base.
To handle storm water, I set my flagstones at a pitch of about 2.5″ fall over 10′ of span. This is the same as saying 1″ of fall over 4′. So as I’m leveling out my stones I can use a 4 foot-level and know that the bubble should center itself neatly, if I lift the level up one inch. In practice, the way that it works is I set up string lines, and get my gravel foundation set at about 2.5″ fall for ever 10′. This number is approximate–for some projects it may be more like 2 inches, or 3. Less than 2 and water might not flow off the patio fast enough and might leave a bit of a puddle that takes some time to settle. If you make the patio much steeper than 3 inches, it could potentially feel like you are on a slant, rather than feeling level.
When I finish laying a flagstone patio, it’s usually about 85 percent wobble free. I then sweep in the stone dust between the joints, hose it all down and repeat, multiple times. After that, I’ll check the whole patio for wobbly stones, and use the mallet to correct any that I find, lifting up stones and placing more stone dust beneath them as needed, malleting them down, sweeping in stone dust and hosing down again. At the very end, the patio may be like 98% wobble free. The flagstones feel rather stable. If you walk around, you may notice a minor wobble underfoot…if you used stone dust as both your leveling agent, and as your joint material, this small amount of minor wobble will correct themselves over time. I’ve never once noticed any wobble, on any of my dry stone patios and flagstone walkways, when I return months, or years later–so minor wobble will definitely correct themselves.
Notes:
•
An inch or so of granite fines (screenings) for leveling the flagstone. No joints wider than a couple inches. Screenings for in between the flagstones.
• Polymeric sand is prone to failing–as described in earlier articles, and many of the replies.
• 1-inch stones are a bit thin, for dry laid. I prefer 1.5- 2.5 thick for dry laid flagstone.
• Just make sure foundation or bedding material is perfectly smooth, and gently mallet each stone into the bedding material. Stones less that 1 square foot in surface area will be prone to not sitting stable.
• When laying out my stones I always place the largest around the perimeter first for stability.
• Ants love sand. Sand with bricks or stone atop it is a big flashing neon invitation to ants who go marching a thousand by a thousand and they all go down to the ground, to excavate your patio! You have your flagstone sitting right on sand and then they will undermine you, and within a few years you will have flagstone with big voids under them, and it will be a big problem.
• Weeds will grow in stone dust, with or without any soil actually getting into the cracks, some weeds will find a way to grow between your flagstones. Tighter flagstone joints will mean fewer weeds. Larger joints will tend to collect more mulch and soil than smaller joints…. soil gets on top of the patio, rain comes, and soil washes right over tighter joints, for the most part. Wider joints catch significantly more soil, because soil that washes on over the larger joints gets lodged in easier. Boiling water will easily kill any weeds between your flagstones–no bending over and pulling needed, no toxic weed killer needed…no need to mix soap+ salt+ vinegar or anything like that (and such home weed killer recipes like that will harm nearby lawn and garden plants as well)–just boil some water.
• The thing about dry laid is it takes a lot more skill. You have to fit the stones tighter, because you are filling the joint with stone dust, rather than cement or plastic-sand. You have to pay attention when leveling out the stones, because you are not just squishing them down into wet mortar. As such, most contractors just don’t know how to do dry laid. I know this because contractors call me almost as often as homeowners do, for phone consultations.
• Don’t overfill the joints with screenings/stone dust. You want your screenings to be a bit shy of the top of the flagstone–if the stone dust comes up even with the top of the flagstones, then the stone dust will easily kick out and spill all over the place. Sweep your stone dust into the joints, then hose down, on shower setting. Leave the joints 1/8th of an inch to a 1/4 of an inch low. You can use the hose to wash out excess stone dust.
• Stone dust aka quarry screenings aka grit aka quarry dust as the final leveling agent.
is it ok to stabilize bluestone rock dust with a little portland cement? my front walk is randomly shaped bluestone with dust in the joints and the lawn crew uses blowers to clear the walk of leaves each week, which also blows some of the rock dust out each week. by the end of the season my wife is upset with how the walk looks. i usually refill the joints every couple of years but that doesn’t really satisfy her. i wouldn’t use a lot of cement, just a little to bind the dust. would i be asking for trouble with this mixture?
Yea, a mix like that will create rigid joints that will crack up, look ugly, and will contribute to the flagstones becoming unlevel. One of the good things about stone dust joints, is they are somewhat self healing. The material beneath the flagstone settles a bit, creating a void under the stone. The stone dust from the joint then settles into that void. Then you top off the joint. With a rigid mortar or polysand joint on a dry laid walkway, when that void forms…the rigid joint sits there, probably cracked, but can’t settle in to fill the void. This contributes to stones becoming unlevel, over the years.
Tell the guys they have to do the walk with a handheld leaf blower, rake/broom if need be–but no backpack blower. A long time ago, I did lawns. I get it, they’re busy and fast moving, and you’ll get some resistance/forgetfulness on their part. Still, to me the request sounds reasonable. In about three months maybe you’ll get sick of the lawn guys not listening and you’ll hire a new crew, who starts out knowing this rule and who’s boss takes on the contract, knowing what the deal is.
Thanks for the article, it definitely helps. How would you change up the filler between the stones if you were doing a “stepping stone” type patio where the majority of gaps are greater than a 1/4″? I was thinking gravel base with sand to place the flagstone then 1″ gravel in between, but I don’t know it the stones would then shift from lack of support from the sides.
Stone dust is the preferred material for leveling flagstones, because ants love sand and may likely undermine a patio built that way.
Stone dust/ DG is a good joint material for joints up to 2″ wide. If you’re going wider than that… I’d consider doing lawn in between. Plant grass seed…or buy sod and cut into strips to fit the joints….or go to https://www.stepables.com/ and find another ground cover you like, thyme or Irish moss or whatever you prefer, and is suited for the local climate/dun exposure. Then buy some plugs.
I hope that helps 🙂
Thanks for the tips! I appreciate your quick response, and love the thourough advice you give. It helps us diy folks have a little more confidence going in to projects.
Thanks for the article / tips. I’m looking at installing a flagstone patio for an art studio in Taos, NM that has one area that needs to accommodate occasional delivery trucks. Do you have any advice for a subbase (concrete, roadway basecourse, etc.) that could take the weight of the trucks and still keep its integrity? What setting bed and joint material would you suggest – also stone dust? I also have conditions where I’m putting flagstone on an existing concrete porch and in other areas that will not receive vehicular traffic. The flagstone is intended to unify all these different areas.
For vehicular traffic, you want at least 8″ compacted road base foundation. Stone dust will be good for bedding/leveling material, and joint material. The two big issues here are flagstone thickness, and flagstone thickness to surface area ration. See a brick, or cobblestone, does fine to cars and trucks. A brick or a cobblestone is defined as a paver. Surface area is maybe twice the paver’s depth. Then you have a flagstone–defined as a slab. The slab’s surface area is much greater than its depth.
A flagstone with a surface area of 1 or 2 square feet, will need to be at least 3 inches. Greater the surface area, greater the thickness of the stone will need to be. You want to use flagstones that are 3 feet by 3 feet wide? You’re going to want a 6″ stone–if its supposed to stand up to vehicular traffic.
I do not have specific numbers for thick…..depends on stone type, partly, but also, it’s very rare to see flagstone that is driven over, by design. More often, it’s cobbles.
I’d find a 4 to 6 inch thick stone to use for vehicular areas, and use the same type of stone, at a different thickness (and greater surface area) for strictly pedestrian areas.
You can dry lay flagstone over concrete. Usually I tell people the concrete really should be pitched in the right direction. Then again, new mexico isn’t very rainy, as far as I know.
Thank you for mentioning how you shouldn’t run into any problems when using gravel to build your patio as long as you get the right kind. My wife and I enjoy hosting family barbecues in our backyard during the summer, and we need to find a way to transport plenty of gravel to our property so that we can build a patio that is half the size of our backyard. Maybe we should consider finding a hauling service that can help us get the supplies we need.
I have a 15′ x 15″ existing flagstone area. they filled it with gravel before and it is mostly washed out and gets everywhere when i leaf blow or the babies crawl on it.
i wam looking at cleaning it out and filling with polymeric sand. the other option is the DG.
does the decomposed granite get hard? and is is still the size of small gravel?
They filled the joints with gravel?
You’ll want to use DG.
Ideally, joints shouldn’t be larger than 2″
If joints are significantly bigger than that and irregularly shaped, then you may want to re-fit the flagstones together better:
shaping flagstones
And then re-level them:
leveling flagstones
Do not do polymeric sand….this article here discusses polymeric sand versus DG (DG wings BIG)
polysand and stone dust
Best of luck with your flagstone patio. Feel free to comment on any of my blog posts with brief questions like this and I’ll be happy to answer….or email me to set up a consultation if you need more in-depth help.
Hi Devine!
I so appreciate your article and have come back to it several times now. We laid our own flagstone walkway over road base and coarse sand (before reading this) now we just need to fill the gaps which are pretty large in most places (2 inches or so). We were going to try and plant a ground cover but I’m not fully convinced on this and keep coming back to DG as a better option. I’m just worried about the possible mess and heard it can stick to shoes and scratch floors inside if tracked in… thoughts on how to prevent this or if we can do a combo of DG and elfin thyme ground cover for a cottage looking path??? Thank you!
Heather,
I’ve never had an issue with DG being “a mess”. First off all, you don’t want to leave your joints over-filled, rather you want the stone dust/DG to be True, a 2″ wide joint is a bit wider than I usually do….but leave the joints a bit low and hose it down real well–if there’s no DG on the surface of the flagstones, than you shouldn’t track any inside.
https://www.devineescapes.com/how-to-clean-dry-laid-flagstone/
(halfway down the page is a section titled “how to install stone dust between your flagstones. which speaks on this matter)
If I was planting thyme in between my flagstones, I’d still fill the joints with a mix of DG and soil. Something like 2 parts DG to 1 part soil. I don’t have a magic formula as to what the perfect ratio is….but the fines in the DG itself are rather small, flour-sized particles of crushed stone, which itself is a not too bad of a growing medium.
I built a walkway a few years back, leaving the joints wide (2″ to 3”) and filled the joints with a soil/stone dust mix. Was at least 2/1 in favor of stone dust, but might have been as much as 3/1. After I finished my work, my client planted plugs of thyme or some similar ground cover. I need to get photos of this one–but anyway, when I spoke with her a year after installation she said the thyme was coming in, but that it was taking a bit of maintenance/patience, to get the thyme fully established.
Once established though, the ground cover itself acts as a joint stabilizer.
So the reason I mix DG with the soil is the DG is heavier/more sturdy than soil, so you’re stepping on a hard surface, rather than soil which may become soft, after a rain. This matters less, once the thyme has fully taken over, but matters a lot, when waiting for it to get established.
Good luck and I hope this helps 🙂
Hi, I have a quick question. My DIY flagstone patio is 5 years old and wonderful, but she small rocks I used in the gaps keep blowing or sweeping out and are a major nuisance to us barefooters. It has been suggested to me that I can simply sweep in some portland cement and water it, and the rocks will be cemented in place. Is this true for a quick fix?
thanks,
carl
Nope!
This is bad advice for a few reasons.
Never use cement–unless you have a concrete foundation. Cement is rigid….dry laid patio is flexible. The cement will crack up. Now you have pebbles and chunks of cement everywhere and the problem is worse.
Not only that but you never use straight portland cement. You mix it with 3 parts sand, or using some similar formula.
You’ve got a few options, but the one your friend or whoever suggested to you, it isn’t one of them.
A. Stone dust if the joints are fairly tight.
B. Stone dust mixed with top soil and planted with ground cover if the joints are wider.
C. ….or just stone dust but make a “moss milkshake” and encourage moss to grow on those joints, if the joints are both wide and the area is shaded enough to have moss.
D. Or larger pebbles, that just barely fit into the joint and that are hammered down into place.
E. Stone dust may also work even if the joints are overly large, but results may not be quite as good/joints may need to be topped off more often.
This article:
https://www.devineescapes.com/how-to-clean-dry-laid-flagstone/
Scroll halfway down to the heading “How to install stone dust in between your flagstones”.
Should I use Portland cement and mix it with Greystone for leveling and to prevent pennsylvania random stone from shifting?
In a word: no.
The vast majority of the flagstones I’ve set have been Pennsylvania bluestone. They do not require Portland cement in order to prevent shifting.
Spend some time reading the articles in the how-to/DIY section of my blog and you will find plenty if advice as to how to set flagstone so that it will not shift over time or underfoot.
this article will help you on your quest
(use stones that are of appropriate size and fit them together well….no cement)
Hi Devin, so thankful I came across your blog. I live in Mississippi and am building a fire pit patio with flagstone. We tried to DIY but that was not working so I am in the process of getting quotes for someone to finish the project. I have a masonry wanting to use Portland cement for the base and joints. I have a landscaper wanting to use crushed limestone for the base and poly sweep for joints. After reading through your blog, I gather I should do the limestone and poly sweep. Is that correct?
Certainly, I prefer dry laid over mortared… But it comes down to the skill of the mason. A well built mortared patio will hold up better than a poorly built dry laid patio. And if “polysweep” is some sort of sand with an acrylic binder–then my answer is no. No polysand, no polymeric sand–use stone dust as the leveling agent and stone dust (aja fines, DG, etc). But again, whatever material is used, it comes down to skill.
Look at their portfolios. Ask to speak with former customer’s.
Related article
Mortar and polymeric sand both form up hard…. And many landscapers and alleged Masons think this hardening of the joint material will allow them to get away with larger joints. Not so. Nothing will substitute for good stone fitting. If you don’t have much faith in their ability to fit irregular flagstones well, then don’t hire them. Or have them install dimensional flagstone.
Best of luck.
Hi Devin,
Have you heard of perk grout and would you recommend it for flagstones?
Thanks
Csaba,
No, I would not recommend using perk grout with flagstone.
This product is like polymeric sand….or like using mortar in between dry-laid flagstone–it’s like those other products, because it seeks to create an un-moving joint material, and use it in a flexible, dry laid application. This is a bad idea, for many reasons that I’ve discussed both in the above article and in another article here.
But the point I want to make here is this:
If the joint is solid, but the foundation is flexible…..then the foundation may settle, or flex, slightly. If the joint howver stays in place, then voids may form, which will cause problems.
Now if the joint material and leveling agent is stone dust, or similar, then you can just top off the joints every once in awhile, and any voids will fill in. Perk grout, polymeric sand, and similar products claim to reduce or eliminate maintenance whereas in reality these products increase the needed maintenance ten-fold.
Hi. This is so helpful. I’m in toronto. Same climate as NY. Had a flag stone path laid (was hardscapen company’s first one) on slight grade. They used this sand that is supposed to harden when wet- it crumbled over winter and there are gaps and cracks.
Another crew came back to fix and same thing happened and a step keeps coming unstable and rocking.
I wanted something more decorative and funky between stones and put some mosaic pieces. They kinda stayed.
I like an organic look but this just looks messy and cracked.
What would you recommend to
Fix this and is there a way to lay coloured gravel
Or bits of coloured tile between? Thanks so much.
You’re certainly going to want to remove all of the “hardens when wet sand”–all of that hard sand, or polymeric sand, or whatever it was. From there, it depend on how wide the joints are. Did they do a decent job fitting the stones?
The best joint material, as described above, and in other articles up on this site, is stone dust/1/4″ minus/DG.
In a best case scenario, you should have a stone dust joint, for stones laid upon a stone dust bed…..and also you should have fairly tight joints, all large stones along the edge of the patio, no tiny flagstones–no pieces too small to remain stable underfoot.
Hi and thanks for posting all of this great information. I have a question, we have had 2 bids for about a 650 sq ft flagstone patio, the first was to put 3″ of course sand (DG) directly on the soil (weed barrier on covering the soil), the second recommended a gravel base and then DG for a leveler. We have selected some pretty large stones some 5’x4′ inter mixed with smaller stones and I am wondering which way to go. Will there be an issue with cracking settling etc down the road, we live in Idaho and have 4 very distinct season but hot summers and cold winters.
Gravel base,DG as leveling agent and joint material. Good luck
I just wanted to say that I appreciate the website you built. I’ve looked for various information for a couple days and your site was better than anything else I’ve seen.
Have you installed Quartzite Flagstone for a Patio? I’m thinking of installing about 1,100SF at my home here in Phoenix, Arizona, but have not dealt with it before. 2 of the shops I can order it from have warned me against trying to do self install due to how hard the rock is and that all cuts HAVE to be cut with a grinder.
Any feedback is appreciated. Thanks!
The big problem with quartzite patios, is that the individual stones are so small. I consider it a secondary minor issue, that pretty much every cut needs to be made with a grinder.
With such small stones, it can be a challenge to get them to sit stable…and, with such small stones, you really don’t have any stones large enough to be edge stones.
I’ve built a quartzite patio once. Customer already had the material, was insisting on using it–despite my warnings. I came by and worked one day, charging my day rate, and in one day built over half of their approximately 220 square foot patio (on a road-base type foundation, already set).
As you can see in the one link, to a photo, I just shared–I set the flagstones length-in, to the patio, in relation to the patio’s edge. Had these stones been set out with the length across the edge, then these edge stones would be less stable underfoot.
1,100 sq ft is a rather large patio to build, if you’re just going to use a material universally regarded as being not the best choice.
Now as far as cutting the stone goes, I did find cutting with a hammer to be nearly impossible.
https://www.youtube.com/watch?v=ReUc33dx794&t=2s
Now since the stones are so small, I was able to fit them pretty well, with only cutting an inch or two nub off of maybe every other stone. But then, I’ve built patios using ironstone/argilite–about as hard as quartzite and much thicker–meaning that it was much harder to cut, and almost all of the cuts pretty much has to be done by saw or grinder…..despite being harder to cut, I’d use ironstone/argilite over quartzite any day–as quartzite is just so frustratingly small.
Hi Devin! We are in the process of laying a flagstone sidewalk that is 5 ft wide by 20 ft long. We dug down and laid 4 inches of crushed gravel several months ago…so it has compacted very well. Then a few weeks ago we laid down about 3 to 4 inches of the fines…screenings (NOT sand). Now my husband is laying and levelling the flagstones and is about 3/4 of the way down the sidewalk. We are debating on what to put between the flagstones…he wants to use a self-levelling waterproof exterior type of grout…I wanted to use mortar as I like the look of it. You seem to suggest using the same screenings we levelled with…but my concern is it getting on the soles of shoes and tracking into the house. Please give us your advice…much appreciated!
Well…..
You dug down and laid gravel and you’re telling me that in a few months it compacted itself. Maybe in 3 years it would have.
The thing is that the proper process is:
1. Dig down.
2. Compact the sub soil with a hand tamper or vibrating plate compactor.
3. Lay gravel and compact in 4″ lifts.
4. Level up each stone one at a time in stone dust, from 0 to one and a half inch–tamping, if it’s going to be much deeper than an inch.
Both sub soil and gravel must be tamped. Soil needs years of sitting undisturbed before it is considered compacted.
Fines are good for a leveling agent…but 4″ deep? Not like, 1 inch–but 4? Uh, did you lay 3″ of fines, then tamp them, and then use 1″ of lose material? Or did you lay 4″ lose?
You can not use grout. The foundation is flexible–even if you compacted it at every stage (which it doesn’t sound like you did) but if you did compact, then the foundation is still flexible. A rigid joint will crack. Polymeric sand is just as bad.
None of my customers has ever complained of fines getting inside.
a) the joints are fairly tight and
b) the joints are not over-filled.
There’s many articles on this site and I offer consultation services if you want individual guidance.
I hope this has been helpful and wish you the best of luck with your DIY stone walkway project.
Hello Devin, I have really enjoyed your comments on website and video clips on YouTube.
Subject: lay flagstone.
I am in Las Vegas area, not too much rain, but sometimes it really pours.
I have an area of 70′ going parallel to the the house, x 10′ wide where the retaining wall is,
between neighbors.
I am levelling and sloping 1/8″ per 10′ as I prepare for flagstone patio/walkway.
I will lay 3-4″ #2 gravel and compact, then will lay 1-1/2″ thick DG and then the Flagstones.
My question is, do I need to run underneath drainage system, to clear out the rain water.
Thank you.
You want to lay your 3-4″ of gravel and tamp that, then lay out your flagstones. Once the stones are all puzzled in, then you go back and level the stones up, one at a time, using the DG.
I describe the process in more detail in this article: https://www.devineescapes.com/leveling-dry-laid-flagstones-how-to/
Usually, in the vast majority of cases, there is no need for any drainage beneath my hardscapes….but in this case, we are sloping towards a retaining wall? Is the neighbor’s yard higher than yours? Or is the retaining wall a step down? If it’s a step down, then water can run over your flagstones and over the wall. If the neighbor’s yard is higher than your however, and the wall is stopping the water from flowing, then a drainage system may be called for.
Channel drain perhaps. You can find 2″ wide channel drains at the big box stores. In some cases, I’ve buried a channel drain, maybe 2″ below the top of the flagstone, and then put fabric over the channel drain, and then covered that with gravel….or even the stone dust/DG. This way the channel drain disappears and is hidden, but still performs its function.
Hi! This is what we have available near us. Would the road base work for under the flagstone pavers with the concrete sand for leveling and in between the joints? Thank you!
https://www.carlingandco.com/products
There’s a product on this page that claims to be road base….but then it says it’s made from a mix of rock and sand. Looking at the photo, it does not look like it contains fines. As such I wonder–will it compact well?
SO I googled Fillmore Utah, since that’s where Carling and Co is located, and found this site:
https://www.oldmilllandscape.com/gravel-road-base/
Their road base looks like it contains fines, and the page claims that it is “Size: 1.5″ minus aggregate with binder for hard-pack.
State spec Road Base.”
That sounds right. By “with binder” they mean that it has fines. Usually I use 3/4″ minus or 1″ minu….but for years I bought from a supplier who only sold 1.5″ minus, and it worked fine. Never had a warranty call. Maybe the larger sized gravel was just a tiny bit harder to rake, but the difference was minor.
The crushed concrete shown on that page would work too. Crushed concrete AKA recycled gravel, will work just as well as crushed stone. May possibly contain asbestos and/or other toxins. If the gravel is dry and you’re raking it out and there’s a cloud of dust…..well, dust is never good to inhale. Concrete dust and stone dust contain amorphous silica, which you don’t want. And if the concrete has asbestos then inhaling it presents more dangers still.
Also on the page I linked to is a product they are calling paver base. I’d use the road base as my foundation, and the paver base as leveling agent and joint material.
That was incredibly helpful. Thank you for taking the time to answer my question!
Hi Devin,
We are in CO and are building a 180 sq ft. Flagstone patio right off the house, more or less touching the concrete foundation. The contractor we are using is using a material called Gray Breeze as the base for the Flagstone and in-between flagstone pieces. We are concerned whether the patio will hold shape and level with just 8″ of Gray Breeze. We are also worried about drainage in this case – he doesn’t intend to grade it and says water will simply drain down through the Gray Breeze.
His approach and recommendation is so different than others we have seen or heard about. Do you think it will work? Or should we redirect this project?
Thank You!
There’s more than one way to do things. Check references and ask to see portfolio. Do his completed jobs look good, and does his work hold up well?
Back in the early 2000’s I worked for a guy who would use screenings as the foundation, leveling agent and joint material. Lay 4 inches of screenings, tamp, lay out all the stones, then level them up using loose (untamped) screenings. Screenings being the local equivalent of breeze–crushed stone, quarter inch and smaller, all the way down to stone dust aka stone flour/fines.
I didn’t work for the guy long enough to ever really verify for myself how well the jobs built like this would hold up–but over the years I’ve came across a few jobs built this way, and they actually were holding up alright.
For my money however, I’m going to use 3/4″ crushed stone as the foundation, and 6 inches of it, not 4. A sturdy foundation material will be less likely to let your stones settle or heave. Colorado, like Pennsylvania, is a cold place and the Earth below us will heave and settle, with freeze and thaw cycles.
Now about this “not going to bother grading” business. Water needs a direction to flow. If the piece of land he’s building on is already pitched in the correct direction, then maybe it’ll be okay? Fact is, a patio needs to shed water, so it needs to pitch. You don’t want puddles to form. Maybe water will drain down through the breeze….but maybe there will be a rainy week, and puddles that sit there for days and days. And what about in winter time–every time the snow melts, those puddles will just be holding ice, that freezes, melts and fre-freezes, in one puddled spot–and too much of that and the stones may deteriorate, de-laminating, spalling, crumbling.
Thank you so much for this blog! I found you while googling polymeric sand and feel like I dodged a bullet. Have since read through a bunch of your articles and am about to embark on replacing my old concrete paver pathway with natural flagstone.
Here’s my question: my existing paver pathway has some kind of gravel/sand base, probably not that deep. These pavers have been in place for about fifteen years, the native soil is pretty hard anyway, and there’s no frost here. My plan for the new foundation is to remove any layer of loose sand slash ant farm I find, leave existing gravel (and whatever is underneath it) in place, and top up with more gravel as needed. Is that sufficient, or should I be excavating further to ensure that the gravel base goes a full six inches deep?
Good question! Yes, if I were approaching a job like this, I would have similar ideas–but I couldn’t say for sure, without seeing the site and doing some exploratory digging. But yea, if the ground has sat undisturbed for 5 years, it’s probably well compacted. Questions I’d be seeking to answer: how deep is the existing gravel? What’s the soil beneath that like–organic, clay or what? Organic is undesirable….rocky clay would be good. How were the pavers looking–level still, or all hills and valleys? Also, how far north are you–deeper foundations are needed, in colder climates.
So if there was a good 3 inches or so of gravel….nothing organic beneath that, and the pavers were looking level….then you might be okay just run a tamper over the existing gravel, top off as needed, re-tamp-and go with it, without any new excavation. I guess the biggest question here is how level were the pavers–if the base was sturdy enough for pavers then it should be sturdy enough for stone slabs.
Took me a couple of days to get to the necessary exploratory digging! It looks like underneath the pavers there’s only a couple of inches of sand, on top of a layer of weed fabric (which has largely disintegrated), on top of native dirt, which is extremely hard — even the parts that aren’t actual rock are sufficiently compacted that I need to really chip at it to loosen it. I imagine the folks that installed the pavers originally got to that layer of dirt and said “good enough” rather than jackhammer it out.
It’s worth mentioning that right before these pavers were installed, this area had been paved over with concrete, so the original layer of dirt under the pavers had been pretty well compacted under the weight of that concrete for several decades. I’m located in San Francisco, on top of a hill where the ground is pretty rocky. Not a lot of organic material; it’s mostly sandstone with what I think is clay in between the giant rocks.
Some of the pavers have shifted and settled a little bit over the years, but none by more than maybe a quarter of an inch; the path is still adequately level as far as walking on it and not tripping. If they didn’t have perfectly square edges that made it easy to compare them I wouldn’t be able to notice it.
Cool. So the ground is well compacted and inorganic and you live in a place where 3 to 4 inches of gravel is considered plenty. Remove sand, lay 3″ road base gravel (if you have room for that much), lay out your flagstones stones fitting them well, cutting/hammering as needed, then level them up using stone dust/pathway fines/DG….shouldn’t be any digging (or not much at all) required in your case.
Sweet! That’s what felt right to me, thanks for confirming. I’ll share a picture of the final product, however long that ends up taking me as I chip away at it one afternoon at a time.
Hope my reply threads correctly this time. 🙂 It took me a couple of months (with a few off in the middle to recover from tweaking my back) but the new path is finished and it’s a major upgrade from the old pavers! Thanks again for all the helpful tips on this blog; I’d never have gotten inspired to tackle this on my own otherwise.
https://www.dropbox.com/s/oeuffseh8l6n5rn/2022-10-24%2017.52.18.jpg?dl=0
Your stone path looks great–definitely an upgrade from pavers!
“Thanks again for all the helpful tips on this blog; I’d never have gotten inspired to tackle this on my own otherwise.”
You’re welcome, and it’s an awesome thing for you to say that, thank you.
Hi Devin,
Enjoy reading your blog and your videos. We just bought a house in the Albuquerque area that has a lot of flagstone paving for a walkway and a patio. All of the pavers are setting directly on the soil. The previous owners placed DG in between the joints. The joints range from pinky width to 2 fingers. Whenever I sweep the pavers the DG comes out and leaves the pavers a mess. The same with a blower. We now have weeds growing out and ant mounds. I’m thinking I need to re-do all of the pavers using DG underneath and using a mortar material in the joints. Do I have any other solution?
Michael,
First of all, never set stones in a lose aggregate (like DG) and then joint them with a rigid material (mortar).
Don’t overfill your joints. Sweep DG in, hose down, sweep off excess, hose down–and when you walk away, the joints should be recessed a quarter inch or so.
Thank you sir, I appreciate the fast reply. I’ll not use the DG underneath. I forgot you did say to use stone dust in your blogs. BTW, your artwork and designs are amazing.
This article is awesome and thank you very much for your expertise!
I have a flagstone porch with flagstone stairs.
The only problem with dust is the stairs on the outside (front) edge of the stairs. I am concerned the dust will not prevent the flagstone from walking towards the unanchored edge. Maybe poly sand for the edge stones and dust for the rest? What do you suggest for front stair edges to prevent the stone from being tippy? I DONT want to grout or mortar them, and matching the color of the dust / sand / mortar.
I saw someone say they used LIQUID NAILS to anchor the outside edge. I DO have the largest stones on the outside edge, as you suggested, but these are stairs so people of all different weight classes are stepping on the leading edge frequently. Will liquid nails underneath be sufficient? What would you suggest?
Polymeric sand will not hold the stone in place. It’s not strong enough to do that, for a flagstone stair.
As far as stairs go–I always set each step riser on top of the tread beneath it–and/or each tread is pinned down by walls on the side of the step of steps.
Some of my dry stone steps can be seen here.
Having said that…..PL loctite https://amzn.to/3LjPQGR is the glue that I would use, if need be. On a new installation–never! My steps will always be properly pinned down. And on a repair job as a professional….yea, we’re going to re-build things and make it proper. But having said that as well…..well, loctite can certainly be used to adhere stones together. There’s been times that I’m repairing cemented in steps–and instead of mortaring the stones down, loctite is used. Some masons hate mortaring down steps and will swear by loctite. Same thing with wall caps, there’s a lot of masons who will use loctite to adhere the wall cap. Back in the late 90’s and early 2000’s, we did use liquid nails some times–but over the years we found loctite to be better. Visit the jobsite 3 years later, liquid nails may still hold, may not–but loctite lasts. Don’t get it on your clothes, will never wash out. Avoid getting it on your skin…because it’s toxic, of course, and hard to wash off. Mineral spirits ASAP, if it needs to be cleaned off of skin, or any surface.
Thank you very much, Devin
I truly appreciate your advice and your pictures of those beautiful stone stairs!
Unfortunately, the flagstone porch and the stairs were installed before we purchased the home.
I really appreciate that this issue could have been originally resolved by properly imbedding the stairs into the surrounding wall. I might endeavor to tear it all up and start again, but in the interim, the LOCTITE is a VERY WELCOME tip, and the tip to keep it off of me in every way, is very helpful too
You are a gentleman and a saint, sir.
To host this is one thing, to be SO RESPONSIVE, I truly cannot tell you how much I appreciate it.
THANK YOU!
Best wishes to you.
You’re most welcome–I’m glad to be helpful
First, Thank you for sharing everything you share.
Next… I am just NOT finding stone dust/ DG out here in the Pacific Northwest. The closest thing I’m able to get is 1/4″ minus granite. It has the fines.
Is that something you would go with if you couldn’t find the stone dust specifically? Am I being too OCD about getting exactly the DG or the dust?
Thank you in advance
Stone dust is aka 1/4″ minus. Or 1/8″ minus.
1/4″ minus granite is good. When I did a project in North California, the local name was “pathway fines”. The only benefit of pathway fines over granite, is the granite costs more.
Thank you for the response and… I can’t thank you enough for sharing everything you share on this site. It’s very generous of you. I found you after I fumbled through a 130 sqft flagstone walkway and luckily before I began to tackle a 300 sqft flagstone patio. I will be making some adjustments to the walkway once I have the patio done.
Thank you again.
Eric
Hi Devin,
I have a flagstone deck around my pool built up on a 3′ high rock wall as my yard is sloping. We need to put a railing on the flagstone for safety so people don’t fall off the 3′ ledge. How would you recommend drilling or not drilling into the flagstone? We need to secure 4×4 posts to the flagstone. What is the best way to secure those posts to the flagstone deck?
Thank you!
This is a simple task but that can some times be tricky. How sturdy are the flagstones and how thick are they? Basically, there’s 2 different ways to mount a post to flagstone: a) using brackets and concrete anchors. Usually using this method for 4 x 4 posts. Or, b) drilling a hole wider than the post, placing the post in the hole, and pouring post anchoring cement around the post.I use this method for setting ornamental steel hand rail type posts, usually 1″ square tubing or similar. In either case, drill through flagstone using an sds hammer drill. Use water too, to minimize dust and extend your drill bit life. Also–start small–drill a quarter inch hole first, then step it up a size…if you start out with a larger bit, it will take forever, will wear down the bit faster–and may be more likey to crack the stone, too.
Hi Devin,
I am not sure if you have advice on stone walls but I figured I would ask what your thoughts are on this project, and if you have any pointers.
This will be at a cabin in northeastern Iowa along the Mississippi River, we get all four seasons here as you can imagine.
I am planning to rebuild a flagstone retaining wall. It will be approximately 4 ft at the tallest point, and I am hoping for it to support a 12x15ft cement slab that will have a flagstone patio set in mortar on top of it. I should mention this will be built on a slope so it will essentially be a raised flagstone patio supported by a flagstone retaining wall.
First, is a flagstone retaining wall likely going to be strong enough to support this design? Or is this destined to fail? I have an array of stones varying between 1-8 inches thick 1-2.5 ft wide and approximately 20-200 lbs.
If this is possible, do you have any general recommendations on the design? For instance, should I dry stack them or should I use mortar or an adhesive between the stones during construction?
I really want the flagstone at the top to be flush with the patio and to protrude partially over the edge of the retaining wall. Maybe just a couple of inches at most, so that it looks like one continuous patio with no border or break. To achieve this look I was planning to glue a capstone that would be flush with the stone on the patio, and mortar between the top layer of stones for a consistent look spanning the patio edge to edge.
Lastly, what do you recommend for drainage? I was thinking of doing 4-6 inches of 3/4-inch clear stone behind the retaining wall and a drain tile pipe at the bottom.
Justin,
Yes, I offer advice on dry stone walls, do consultations for dry stone walls, and have written how to articles on the subject.
I have built many raised patios that have dry stone walls supporting them. All of these have been both dry set patios AND dry set stone walls. I can see zero reason to mess around with a concrete foundation for your patio.
Grade level cement–in any northern climate–will crack.
The secret to making a dry laid patio supported by a dry stone wall:
Use larger, heavy stones around the edge. (which is what I always recommend even on a non-raised patio, anyway)
The wall material you describe sounds fine–but why are you calling it a “flagstone” wall? Flagstone, is flat stone used as paving. If you took a pallet of flagstone, you could use it as wall stone….but then it would no longer be flagstone–it would, by virtue of how it’s being used–be wall stone.
As for drainage–dry stone walls and patios are both freely draining. No need for a perforated pipe, clean gravel, or filter fabric–these I bring out only in the most extreme of situation….or if for some reason you are forced into having the patio pitched the wrong way and we have negative pitch that needs to be dealt with.
Hi Devin, thanks for the pointers. I appreciate it. I am using limestone for the patio and retaining wall.
Additionally, I am reusing the stones from the previously existing patio that have good structural integrity to keep costs down.
The area is remote and I can not seem to find a nearby source that has nice stones for purchase. According to the quarries nearby they now blast stone such that they do not have the wide/even/flat qualities.
However, this property has a lot of naturally occurring stone all over the place. Some of which is too soft, and is prone to splitting and crumbling – those pieces I do not use. But I might end up scavenging for some good stones around the place.
This is at a cabin my grandfather built, he was a contractor and a very creative and skilled guy. He used limestone all over the place stacked horizontally with mortar on the pillars, arching over the front doorway, behind the wood burning stove. Nonetheless the feature that is most striking to me is definitely the floor.
It is limestone or some kind of sandstone that looks very similar to limestone (I’m no stone expert by any stretch). He did this inside the main living space, four seasons room, on the covered porch and even a small stretch of patio that is uncovered. All of which has been laid on a concrete slab with mortar.
The crazy thing is contrary to what you mentioned about cement cracking which I am aware in most cases it does. None of these areas have cracked. Although there is a stone or two inside that appears as though someone dropped something solid and heavy on and hairline cracked just the stone.
Even the outside covered and uncovered areas have no cracks on them. Prior to obtaining the place last year, this cabin has not been up kept in the over seven plus years since my grandfather died.
So I wanted to take the horizontal stacking design from the pillars/archway/behind stove for the retaining wall. For the patio I want to continue the design of flagstone in mortar on cement as it feels like the right look for the place if at all possible.
I should mention the patio that was there before was a different design. It was dry stack stone on the retaining wall. Which the retaining wall more or less seemed like an extension of the foundation as these stones were buried deep into the foundation of the raised patio in the dirt and sand.
The top stones were laid into sand. Which caused several problems. Stones sinking and sand spewing out between the stones and splashing sand and dirt mix onto the patio door and siding during every rain. I understand it was unkept but I always thought this design paled in comparison to the other stone work on the property. I remember initially it looked pretty cool. But it just didn’t work or last in the long run.
The base is primarily sand over a foot deep. So I am kind of lost in what the best method is to do this place justice that will last.
Sorry for the lengthy details, i am simply trying to paint the picture for you. Any other ideas or comments that you can share?
I really respect your work, your gallery is incredible. I look forward to hearing from you.
Dry laid versus wet laid_–which one lasts better? Whichever method was applied with more skill and sincerity. Avoid laying flagstone on sand–and never lay on a foot of sand! cemented in works, when they fail, tend to fail catastrophically. Dry laid works tend to need a little maintenance after !5 years or so. MY own cemented in works and dry set works still look good after over !0 years though.
Confused though, as idk what stone you had that was set on sand– wall or patio? Either way, wrong move. For patios, if you use cement you”ll get a few years without weeds (that”s the only real benefit) until it begins cracking…..short term low no maintenance, long term is likely to fail and require complete replacement. Unless it”s down well. Use either system poorly and watch it fail use either system well and enjoy it for life.
Hi Devin,
I do intend to complete this project myself. However, I’d like your official recommendation on how exactly you would go about this project.
I definitely want it to last but also jive with the overall look of the place.
There might be some aspects I need to move past, from a design standpoint. I am open to that but hoping I can make something that will provide some continuity to the original look.
I’m happy to pay for your time, I’m not requesting an on-site visit. But I can provide photos/video of the site and the stones I’m working with. Additionally, I’d like to show the stone work throughout the cabin that I am trying to replicate.
I’m very determined to see this project through despite being new to working with stone. I really enjoy a challenge and am not afraid of failure, although I’d like to avoid it if possible.
Let me know what your thoughts are and if we can schedule a time to discuss further.
Thank you so much for your help, it means a great deal to me.
Justin,
Sure, we can set up a consultation.
Often it’s best to make your work look good, with available materials/appropriate materials–right next to someone else’s work–by just doing it right, rather than trying to copy what someone else did. I can speak more specifically on the matter, after seeing photos and/or video.
Send $123 https://account.venmo.com/u/Devin-Devine-3 and Email me at devin@devineescapes.com to set up a time. Looks like I’m flexible tomorrow any time after 1 pm
Great Info – I’ve spent hours reading your comments!
Making a flagstone path and would like to put mosaic pieces, stones etc. in between the flagstones – right now I have decomposed granite as the filler. What can I use to set the mosaics in place and do I need to remove the DG?
I’ll share with you my secret–but only after you promise to post a photo of your mosaic work, here in the comments on my blog, once complete.
Hi there! I have just had all the old cracked filler removed from my gorgeous large flagstone patio and was going to use Gator Polymeric Stone Dust ~ not cheap to buy, fill or clean. So am stalling out on that and instead reading articles like yours. The gaps vary in width however, not hugely but they are not all 1″ joints…some are more in places, like 2″. I want to use DG and the method you describe of brushing it in, watering it, sweeping and then again until it is about 1/4″ deep from the level surface. My question: will this still work gaps wider than 1″? Do you recommend tamping it down while wet? Any other toppers to hold it in place? Any other ideas? Thanks a million.
No tamping involved. Just hose down. 2″ joints aren’t a problem. My consultation customers often email me photos of their completed projects, usually with gaps much wider than how I fit my stones. No one has ever complained that their wide joints were getting washed out too often. Smaller joints look better==and smaller joints are a good indicator that a someone who knew what they were doing did the installation–but 2″ wide joints are acceptable for dry laid flagstone, with stone dust joints.
But wait–the original material was cracked up? So was the original material mortar? If so, is the flagstone set upon concrete?
If the original job was dry laid, then top off joints with DG.
If the flagstones are on concrete–then repairs should be done with mortar.
Hello, Devin,
I’ve just spent about an hour reading your posts and comments. I’ve learned some very helpful things from you!
I have completed some flagstone steps, ready to fill the joints- but cannot figure out how to contain the DG so it doesn’t spill out of the front of each step. I made a 1” overhang on each step, so the front edge is not flush with the riser below it, which is made of bricks. So, trying to figure out how to close of the front ends of the steps do the DG doesn’t spill out.
Another thing- I had some serious spalling occurring on my flagstone patio. Got it all cleaned up and repointed the cracked/loose joints. Do you have any advice on preventing spalling? Have had some unusual ice storms here in Texas .
You’re amazing!
Katherine,
When I have flagstone that I’m setting on top of a dry stone wall, either for a raised patio or for steps as you describe–there’s a few things I do.
The joints are set tighter than usual, and often become really tight, towards the outer edge, where material might spill out. So the joint might be half an inch wide except for the outer last inch or two, here it joins up, two stone touching. Alternatively, what I often end up doing, is setting a sliver, a few slivers, or small chunk of stone, usually a flagstone fragment– wedged into the joint, towards the edge. The wedged stone, and/or tight joints usually stop most or all spillage. But, if the joints don’t stay 100 percent full, 100 percent of the time–then so long as the steps function wobble free and look good, then it doesn’t matter so much.
I avoid spalling by being selective with my stone purchasing, buying the most solid looking material of what is available, and refusing to buy stone that looks like it wants to de-laminate, open like a book, or flake up. But this is a patio that’s already built and maybe has some age to it. If ice and snow come, then I’d remove it, just so that it can’t melt and re-freeze. If that is even a possibility where you are, idk. Protection from the elements: if you can put a roof over it, will help, possibly a lot.
Quick question, moved a retaining wall, area that is now open, has been undisturbed for over 20 years.
Want to make it a flagstone “patio”.
Going to make sure the gound is “leveled”, slight slope away from house for rain run off.
Going to tamp the ground since I will be doing some disturbance to ensure the slight slope away from the house, clay mix in my area.
Do you recommend vegetation barrier before starting with your instructions using the stone dust in this blog?
In a word: no.
Landscape fabric/weed barrier would add no value in this case–certainly won’t help with “weeds”.
My foundations for patios consist of a tamped sub grade, 6″ or so of road base type gravel/2a (regional names vary) also tamped. Then flagstone gets laid on top of that, then each stone is leveled up, in stone dust.
If you put the stone dust beneath the gravel–then dandelions/unwanted plants will have 8″ or so of material to grow between, before they encounter that barrier. Anything that can get through 6″ plus of gravel, is going to go right through that fabric.
But if you put the fabric in between the gravel and the stone dust…..
Then 1. the fabric will get destroyed as you lay out the puzzle and 2. some stones end up being too high and you need to lower them into the gravel bed–see the problem? Fabric will be completely in the way at this layer–plus, it will do no good.
Hi Devin –
So happy I found your blog before I did something I might regret! I am looking to lay irregular flagstone (thermal, 1.5 inches) over an existing concrete pool deck here in Pennsylvania. The pool deck is 40+ years old but structurally sound. The look I want to accomplish is very much the same as the flagstone pool deck you did in Northern California circa 2018. Given this project involves a pool deck in Pennsylvania (i.e., subject to moisture, freeze/thaw cycles), I’m unsure as to the optimal method to lay the flagstone and fill the joints.
My current thoughts: Secure the flagstones along the edge of the pool (coping) and fill the joints using a polymer-modified mortar such as Ardex X3 Plus; secure the flagstones composing the outside border using the Ardex (but with pathways in the mortar bed so that water can drain out); and lay the flagstones ‘in the field’ on stone dust and also use the stone dust to fill the joints.
Am I on the right path or wandering aimlessly!? Again, we’re aspiring to replicate a look quite similar to the CA pool you did. Thanks in advance for any thoughts or suggestions!
Question: bought a home with large flagstone patio. Not sure what it was set on, could just be soil, because it certainly appears to be dirt in between. I have tried the sand they sell for filling in between, followed all the instructions, but it doesn’t do much to hold back weeds. So many weeds!!!! I’m wondering is there any creative way I can fill in gaps to prevent weeds? I saw what you said about cement being a real problem to repair if it cracks in future, which was my first thought, so now I’m back at square one. Maybe spray with that glue that you see people using to glue pebble beds together?! Any help appreciated. Thanks!
Fill it with stone. Fit the stones together better, closer–so there’s smaller gaps for plants to grow within. Or fit smaller, decorative stones fit tightly in between the larger flagstones. Don’t spray any glue!
About weeds and hardscapes.
Devin: I have just had my contractor install a 68in wide pathway about 80ft long around the side of my house from my driveway to my front door. The pathway base is compacted 5/8 minus gravel. I now want to install flagstone. 1-Can I install the flagstone directly on top of the compacted 5/8 minus (no further leveler needed)? 2-can I use decomposed granite as joint filler as opposed to using more of the 5/8 minus (the planned joint gaps will be 2-4 inches) and if so, what would be your instructions for actually filling those gaps? 3-If I am not on the right track, what do you recommend I do differently? Thank you.
Build your foundation, get it well compacted and pitched right, then lay out your flagstones. Once all the flagstones are laid out, go back and level the stones one at a time, using stone dust as a leveling agent and joint filler as well. Decomposed Granite can be used as a joint material, but it is usually more expensive than stone dust, which is crushed sandstone/limestone/argilite, and it does the same thing. More info can be found here.