Flagstone Maintenance and How to clean dry laid flagstone
How to clean an older, dry laid flagstone patio and then how-to replace the material between the stones
This question comes up sometimes: people ask me, “how do I clean my flagstone, without removing the stuff from between the joints?” Since I am your hardscape helper, I figured I’ll toss you a little lesson.
Professional flagstone advice
As a flagstone patio ages, it can gain a thin layer of grime. You may notice your patio stones darkening in color, over the years. This may or may not be much of an issue for you. Often, the flagstones will darken slightly, but it still looks great, so who cares? Other times, the flagstones may darken unevenly, or in a manner that is otherwise unappealing. Often, it’s just a matter of taste. The worst though, is if your flagstones become slippery, with the grime of the ages. If that happens, then it’s probably time to clean that patio!
So everyone’s first thought is the power washer AKA pressure washer. But everyone asks me, won’t that remove the stuff from the joints? Of course it will! And there’s really no way around it.
But it’s not so bad, really. We’ll get through this. Together.
So you have two options, really–one is scrubbing. The other is power washing and then re-filling the joints. Either option takes a bit of time. But don’t fret, you can do it!
How to clean dry laid flagstone: Pressure washing
- First of all, I’ll usually recommend scrubbing with a scrub brush and soapy water. A wire brush for the worst spots. But if you insist on using a pressure washer to clean your patio, then here you go…
- Have the machine on it’s lowest setting, at least at first. A powerful pressure washer can, and will destroy flagstones.
- Start out in a seldom trafficked part of the patio–just in case you do end up damaging the first couple stones you try and clean.
- Get the whole patio clean and let the old joint material get washed out, it’s no big deal, really. I can fill the joints on a thousand square foot patio in an hour or so.
- Let the patio dry. Go have yourself a sandwich.
How to install stone dust in between your flagstones
- Get out you shop broom, one of them big broad brooms, not a
kitchen broom. - Put on some tunes. Something that makes you smile and/or dance.
- Dump out a 5 gallon bucket of screenings AKA stone dust AKA decomposed granite–or whatever joint filling material you are using.
- Spread that stuff all across your patio, going back and forth over the joints. Get the whole patio covered and all the joints filled.
- Broom off most of the excess. Sweep it up into a pile and get it back into your bucket or wheel barrow. Most of the excess–you don’t need the patio stones clean of stone dust, not yet.
- Hose off the entire patio. Hose it down. Soak it. I usually use a shower setting, if available. Many joints will just sink, as the stone dust settles down into the crack. That’s okay, you want that to happen–we want all of them voids to get nicely filled.
- Let it dry.
- Cover the patio with stone dust again and repeat the sweeping step. Sweep it in, patiently. This time, try and get the patio a bit cleaner, less dust on top of the stones then last time.
- Sweep up into a pile, again. Hose down–again.
- You may have to go for a third pass. Probably you’ll just want to do a spot fill. Look for and find whatever spots need more stone dust, and top them off using your hand, or a small hand brush–either a masons brush or just like a little dust-pan and brush type brush.
- Lightly hose it off for the (hopefully) final pass. Let the hose push the remaining dust from atop the stones into the joints.
- Let it dry.
- If there’ still a bit on top of the stones, I’d hit it, carefully, with a leaf blower.
A flagstone patios joints can never be truly “flush with the top of the stone”. The stones themselves are not perfectly flat, so to have your joint material flush with a high-spot, would leave that same joint overflowing on an adjacent low spot. Early in my flagstone patio career I used to try and keep the screenings in my flagstone joints as close to level with the stones as possible, but with foot traffic, wind and rain, the joints seem to naturally level off to around an average of one eighth of an inch shy of flush with the flagstone.
this is how you do it
That wasn’t so bad, was it? Hey, I do this stuff all the time. So do my helpers–and we never complain! Hey, the task is not super easy, but you’re outside, birds are singing–and you have an awesome flagstone patio. Life is good!
Note, if you are using screenings as your joint filler, like I recommend here, then the joint filler will stiffen up a little bit, and become almost semi-solid, after hosing and drying a couple times. That’s because the stone dust (screenings) contains both 1/8th inch chips of stone as well as fine, flour like dust. The dust hardens up a little, when made wet and then dried.
How to clean dry laid flagstone with a scrub brush
- Get out your scrub brush and put on some knee pads. Also grab a wire brush–preferably a wider wire brush, like one of the ones that’s 3″ wide, not a 1 inch wide one.
- Go and try the scrub brush–with a bucket of soapy water.
- Didn’t work? Fine, get wire brushing. HINT, you will need to wire brush–if the flagstones are dirty enough that you feel they need a cleaning, then yeah, the wire brush is what it’s going to take.
- Wire brush each and every stone clean. Then hose it off. Still dirty? Sorry kiddo, better put them knee pads back on….
- Repeat until clean.
- After all that brush, right next to the joints, and all that hosing, you will have lost some of the joint filling material, sand, soil, or stone dust, that was in the cracks between your stones. No biggie. Scroll up and read the “Re-filling the flagstone joints after pressure washing” part. Since you scrubbed, you won’t have to do nearly as much work as this, but the guidelines still apply. Take stone dust, sweep it in, hose it off, let dry, repeat/spot check, as needed.
So there you go, free DIY advice from flagstone professional and stone mason. If you need more help, then I will direct you now to my consultation services. And I look forward to hearing from you.
DIY Flagstone and Hardscape help
My rates for DIY consultations are as follows:
$80.00 for a half hour consultation
$115.00 for a full hour
Monies are payable via paypa, Zelle or venmo also accepted.
Thanks for the great information!
I am pressure washing my flagstone patio now, and after initially trying not to blow out the joint filling, I have decided not to worry about it, and refill the joints when finished. Once you decide not to worry about it, the job goes pretty quickly.
my one tip is make sure you don’t aim the pressure washer straight down between your legs, or all the gravel will come shooting up your shorts.
My patio is kind of old, and many of the joints are now covered by a layer of dirt and moss. I think i am going to purposely blow than material out and replace it with stone dust for a “cleaner” look – is that okay?
Sure, nothing wrong with that.
A flagstone joint that has naturally filled with soil and moss over the years will be very stable. Such a flagstone joint will be more stable usually, then a flagstone joint that is filled with stone dust.
Stone dust joints are usually pretty stable too mind you, just not quite as stable as moss filled. Anyway, totally a matter of preference, so either way is cool.
If any of my readers have more questions, I would suggest that you read more of the how-to section of my blog–and if you still need more help, I also offer phone consultations.
Good luck with you patio, Jeff!
Devin, really grateful for this site. I live in Phoenix. I am laying a flagstone patio. I read your article on plastic edging as well as this article.
My question is, while the screenings won’t wash out from the inner joints, what about the outer perimeter joints which are exposed above ground?
Thanks
Nathan
Outer perimeter joints are a) not above ground. The flagstone is even with the ground. And/or they are tighter than the rest of the joint. What I mean to say is that for my flagstone patios, you’ll have a joint maybe as wide as my pinky finger. But at the outer edge of the patio, the the joint tends to narrow up a bit, and many of the stone will actually be touching, or close to it, at the edge.
Sometimes the flagstone are above ground, as in the case of flagstone steps, or the edge of a raised patio. In such cases, it’s as outlined above–the stones are touching at the outer edge, and they come a bit tighter than on a regular flagstone patio where the stones are basically flush with the ground.
Sometimes with steps and with raised patios, some of the screenings may wash out and leave a five inch span of empty joint. Honestly, no-one has ever once complained over that and it’s just never been an issue. Mind you, I’m meticulous and generally avoid the situation–but it does happen. Anyway, another trick that I’ll use, in the case where the flagstone is higher than the ground for some reason, is I’ll wedge in some pieces of gravel or flagstone fragments, right near the edge. So the flagstone will come together and close the gap, and also, an inch or so before the edge, there may be a flagstone fragment, wedged down into the joint, intending to dam up the gap and help slow the loss of screenings.
Hopefully that makes some sense 🙂
So, I finally finished one of my two patios, and the problem I am having now, is that when my lawn guy uses the leaf blower to clear leaves from my patio, he is blowing the tiny stones from between my flagstone out onto the patio.
it seems like a few of the spaces between the stones got filled with a mixture of stone fragments and dust that was more dust-rich than other spaces. these seem to have solidified a bit, and are more resistant to being blown out than other spaces, that are mostly filled with stone fragments and have less dust.
Will the stones eventually stop getting blown out?
did I maybe use the wrong filler?
this seems like it might be a big problem – right now I have to clean the patio, as it has a lot of stones on it and you can’t walk on it with bare feet.
I don’t want to have to clean it every time the lawn guys come.., and i am afraid that eventually there won’t be enough between my flagstones.
i have one more patio, and i am thinking maybe i should use polymeric sand…
Do not use polymeric sand for your flagstone patio. Unless you want an expensive, difficult mess and a giant waste of time. Being honest, that’s about the best that I can say about polymeric sand! Here’s an article, which explains in some detail, how polysand really is not appropriate for use on flagstone patios. Read the comments–many many people agree.
So it sounds like you already know what the problem is–the material between your flagstone joints is not consistent. Some it it has fines, or stone flour–that flour-like stuff that is the smallest size of crushed stone–the stuff that binds up when it gets wet. And some other parts are missing the flour–if it’s just eighth inch chips of stone, with no fines, then it will be subject to blowing out.
So spend ten dollars and get some new stone screenings for your flagstone patio..
And/or….just tell your lawn mower guy to cut around your patio without blowing grass unto it–and then he’ll have no reason to use a leaf blower. No, it really is that easy…..when I used to cut lawns, there would always be places where we were not supposed to blow grass clippings….and it’s a pretty small matter to cut those regions (like garden or whatever) with the mower pointed the other way, so the clippings go someplace else, away from your flagstone patio.
HI
Really informative blog. Appreciate your advice. My flagstone is in a walkway, interrupted by 3 sets of stairs. You gotta love these hills side desert yards! There are 26 stairs in all.. Because of this our flagstone has cement between them. So I don’t know about “replacement” of these areas after cleaning. I did not see this question addressed. Any advice would be greatly appreciated.
I recently wrote this article, describing the process we use for re-pointing flagstone: https://www.devineescapes.com/flagstone-walkway-re-pointing-and-repair-in-paoli-pennsylvania/%
Put simply:
1. remove old mortar, at least a half inch down
2. clean out the joints real well. Hit them with a blower, then a hose, then a blower again. Get them clean as you can.
3. use really dry mortar. This is the BIG TIP, the pro tip–you want to add just enough water to your mortar that it all darkens, but that it doesn’t enough hold together on it’s own, it only holds together when firmly pushed down into the joint between the flagstones.
ALSO, I wrote this earlier article, describing the flagstone re-pointing technique that I used to use. Basically the same as my current method, only with slightly damper mortar and then with more clean-up afterwards as well.
Hello! We had a flagstone walkway put down last summer. They used the polymeric sand. We had no idea that it should not be used. They are a local landscaping company with an excellent reputation. Now, I’m worried about the polymeric sand. It looks like some of the flagstone isn’t level any longer. Aiso, they told us to put more polymeric sand on. We still have a half of a bag left. Your suggestions? Also, is it normal for a big chunk of the flagstone to break off? What should we use to reattach it? Also, we have had some of the very thin top layer come off.. Is this normal?
I tried cleaning it & some of the stains (wear) do not come out? I’ve read where some people recommend bleach & water? I thank you for your help!
The project was done wrong. My suggestions are to use stone dust–not polymeric sand. Once the polymeric sand is in…..my advice is to remove it and replace with stone dust. The problem is that typical landscape contractors–including local landscape contractors with great reputations–tend to use polymeric sand in replace of having good stone skills. My bet would be that the joints are too wide and also of irregular width. I’d also bet that some of the stones are too small. The polymeric sand allows large joints to stay stable–until the polymeric sand fails. Which it will. It also kinda glues stones together, temporarily. So if you were to just remove the polymeric sand and replace with stone dust, you’d have these huge irregular joints, that wash away when it rains, and stone dust would kick out and get all over the place under regular foot traffic. And tiny stones would pop up and come loose.
So, you’ll need to remove the polymeric sand…and have a skilled stone mason who who knows his flagstone work come out and re-fit the stones together better.
I have no advice about cleaning that gunk off your stones. I’ve only had luck using an oxy-acetaline torch myself…..
Can you please email me some photos of the stones that the very thin top layer is coming off of? I’ve been researching this problem and plan on writing an article about it soon. It seems like it is yet another polymeric sand related problem, science is not certain, just yet, but I keep seeing flagstone jobs where polymeric sand was used and then the top layer of the stone peels up, like paper-thin layers of stone just de-laminate, which is a thing I have never encountered on flagstone that is jointed with stone dust, sand, or mortar. Regular spalling is one thing, and bits of stone will flake off, but the paper-thin layers coming off all over the place seems to be uniquely associated with flagstone that was set with polymeric sand. So please email me a photo at devin@devineescapes.com
And good luck!
Hi Devin, Wish I’d found your website before I installed a flagstone patio last year. I live in a very wet section of the NC mountains and with the rain & snow of the past year my flagstone is flaking up. Do I need to seal my flagstone? I also need to refill the spaces between the cracks. Is sand or stone dust better? Thank you for your help.
Sealing won’t help. Sealing may prevent water from getting in to the top of your stone….but moisture can still may absorb from below–or from imperfections in the seal. But then the seal traps moisture in, not letting it evaporate.
Stone dust is better as a joint material. Ants love sand, and may excavate sand joints, plus, sand tends to wash away from rain and wind, whereas stone dust stays more in place.
To avoid future flaking up: make sure the patio is pitched right, to shed water. If you were further north I’d warn you about not letting snow accumulate, then melt then re-freeze on top of your flagstones, as that’s what often causes such flaking. In your case, IDK if the stone wasn’t the best stone, to begin with, or if it may have been damaged, or what. Maybe replace the worst stones if necessary, but sometimes minor flaking up isn’t really a problem.
Devin, here I am again! I just love and appreciate reading your articles. My patio has long been finished–in November–THANKS to all your lessons and advice. You are the absolute BEST! There should be a fee to visit your site. You provide such in depth, complete and clear guidance!
Annie, hey no way–you’re the best! I’m glad you found reason to visit my website again 🙂 The website shall remain free of charge and I will continue to provide the best advice that I am able. Meanwhile I am also writing a book on the subject of natural stone hardscaping. I will charge for that 🙂 Thank you!
I had a slate colour flagstones installed. My husband power washed them and he has left lines all over them. I could cry. Is there anything I can do? Will putting a satin or wet look seal on them take it away?
Sealing won’t help.
Depending on the stone type, there may be another remediation available though. If it’s bluestone, granite, or any sandstone– then I’d just torch the problem spot for a thermal finish.
If the flagstones are actually slate–then I’d try sanding them. Start at 100 grit, work up to maybe 800 grit. Sand the entire stone, working it up to a uniform finish. Might do the sanding if the flagstone is limestone, too. If the stone is an argilite–then either fix will work.
Upload a photo to imgur.com and then post the link here for me to see, and then I can hopefully answer better. Also–where are you located?
We laid a creekstone walkway with irregular and large spaces between the rocks. It is sitting on a sand base. After reading your article i was planning to lift the rock and put a layer of rock dust under it and then between the rocks. As I kept reading though, it looks like the dust won’t work because the spaces are too big between the rocks. Do you have any suggestions? Unfortunately, the ants are having a heyday with the sand between the rocks.
You’re already lifting up the stones in order to replace the sand with stone dust…now is the time to tighten them joints up a bit. It doesn’t have to be perfect….but if you can improve on the stone fitting, you’ll extend the life of your patio/minimize maintenance–both by having less wash-out and less weeds.
Now ants are known to love sand. In all my years I’ve seen one, maybe two situations where flagstone laid in stone dust was having problems with ants. So they’re not big into stone dust, but then it is possible…..and since they’re already accustomed to having lived there for a awhile….idk. I’m just warning that I can’t guarantee that replacing the sand with stone dust will make everything better and will chase off the ants. They already live there, they may come back. I assume it will improve the situation somewhat–because I’ve still never seen a patio in stone dust that was actually undermined and un-usable because of ants–but I’ve seen that a few times, with sand.
Anyway, just do your best to try and fit the stones a bit closer. Here’s a video of me cutting a piece of flagstone, using a brick hammer:
https://www.youtube.com/watch?v=ReUc33dx794
That video, combined with the following article, will provide you with guidance on how to get your flagstone fit together a bit better:
https://www.devineescapes.com/how-to-natural-flagstone-landscaping/
This article here will be helpful, for the re-leveling process:
https://www.devineescapes.com/leveling-dry-laid-flagstones-how-to/
We love on the lakes region of NH. We have two blue stone patios. One without a covering and one covered and just outside our basement doors.
The covered patio is always dusty, like the stone is disintegrating. Is this my imagination? Is it just the result of not being exposed to rain?
By the way, installation was 8 years ago by a professional.
If the covered patio is actually disintegrating and is in worse shape than the uncovered patio–that would be a big surprise. A covered stone patio is protected from the elements, so even in a southern climate, the covered stone is expected to last longer–in northern place like NH, the winters can be quite hard on exposed stone.
Considering this, I expect the covered patio is just dusty, and is not deteriorating….unless there is some unknown factor at play here.
Devin,
Thank you for your amazing resource on the internet!
One question regarding a flagstone pathway around a concrete patio. We get a lot of small tree debris from Douglas Firs and Cedars. It seems using a leaf blower would remove decomposed granite/quarter minus over time? Is another option is to space the flagstones a bit wider and use soil for the last (inch?) of filler and get a proper ground-cover established? I do love the look of a pathway with vegetation between so it seems like that would solve being able to (monthly?) leaf blow it and remove the tree-fall debris from the stones and space between. You seem to suggest just use the decomposed rock with fines and refill it periodically, but would vegetation be a secondary alternative?
Thoughts?
Much appreciated!
Matt,
Yes, vegetation is a good option.
I do want to note that in my experience, it is not much trouble to clean off the top of flagstone using a leaf blower, without disturbing the quarter inch minus from in between the flagstones.
Rather than using topsoil for the top inch of the joint, what I have done is mixed the quarter inch minus with top soil, 2 parts stone dust/quarter minus, to 1 part soil, mix it up, plant a ground cover. I’ve seen Irish Moss, regular moss, and creeping thyme all used to good effect. Apparently it takes some work getting the plants established…..you plant plugs, six inches or a foot apart from each other….water it for a season, to get them started…..pull out some unwanted weeds, and maybe add a few more plugs next season…..but once established, you have a stable joint, that will won’t require periodic topping off, the way my usual stone dust joint does.
You may find something to plant in your flagstone joints at your local garden center, or possibly already growing in your own yard, or at this website, dedicated to selling foot traffic tolerant plants.
Devin,
Thanks for the prompt and detailed response! I extremely appreciate your suggestion about the mix with the stone dust with soil, that’s a good idea and makes sense for striking a balance between planting vs helping secure the stones and have a solid base between them. We don’t mind the up-front work of planting and some early on (first year or two) maintenance if we can get them established.
That website is great as well, thank you, we are already finding some suggestions that work for our climate (western Oregon).
Final question, and if I have any more I’ll schedule a consultation. Given this is intended to be a rustic pathway with vegetation, more of an accent around the cement patio, and not a high trafficked route, is maintaining the tight spacing less critical? I’m trying to mimic what I see when I google search for flagstones with ground cover and I see a lot of examples that at least look good and the spacing is much much wider.. But so much of your advice focuses on taking the time for tight spacing. I guess does use/application affect that in your opinion?
Thank you again
Matt,
Yes, if you have plants growing in the joints, you can leave the joints larger and you should leave them at least a bit larger, than I usually leave mine. For a planted joint, I’d go with a 2 inch joint…if you went with a half inch tight joint, then it can sometimes be harder to grow stuff. Moss will work, in a tight joint though. I still prefer to take my time and keep the joints consistent, as this is one key factor that is often crucial to whether a stone construction looks good or not–having consistent joints. Mind you, with a 2″ joint, you have a bigger tolerance. A half inch joint may look off, if you vary it by a quarter inch….if there’s places where the joint is quarter inch tighter or wider, than other spaces, that might be a bit more variance than you’d want, aesthetically speaking. But with a 2″ joint, you won’t really notice a quarter inch variance.
Having said that…..depending on what ground cover you use, it is possible to make a stone pathway pretty, despite the joints varying widely and being irregular. As a pro, idk, it’d be difficult for me to leave wide, irregular shaped gaps, but I have seen situations where giant, oddly shaped joints were planted with lush/flowery ground cover, and it looked pretty good. There’s an exception to every rule then–but it is a pretty solid rule, that the more consistent the joints, whether tighter or looser, is key to making any stone installation look good.
Devin,
This project sure took a lot of work for me with rainy days and weekend plans etc, being a perfectionist about slope and making sure stones had no wiggle to them, but finally wrapped it up last night! https://imgur.com/gallery/ktuElk8
You’re right, I’m not having much issue with leaf blowing stuff off it. Lose a little bit of the DG but not much. It’s been very wet here in Oregon and I think it could really use some cycles of wet/dry to help it lock in more.
We’re going to see how it goes through this winter, if any moss establishes (it’s Oregon after all..) and will buy some specific plants (Cushion Bolax/Azorella trifurcata) in the spring to put in the larger gap areas.
It’s not up to the tightness you’d put in but we wanted a little more organic transition from concrete to grass, not just a concrete alt. Your site helped tremendously!!!! it is the authoritative guide on doing flagstones right! such a wealth of information. Thank you thank you thank you!
Matt,
Your hard work has paid off–the flagstone/patio extension looks awesome! Very glad you found my articles helpful, and thank you form posting the completed photos 🙂
Devin,
Thanks to your instruction my flagstone pathway is still awesome as ever! But I recently had a tree cut down and surprised, looks like bar oil was spilled/dripped onto about 7 flagstones.
I tried warm water and dawn dish detergent with a nylon brush and then a fine wire brush, to no avail. It’s not greasy anymore but it is discolored. I think the oil sat there for about two days. Boiling water? pressure wash? Special cleaners?
Suggestions? Thanks in advance
Based on my experience, it’s probably not coming up. A pressure washer is the next thing to try, or muriatic aicid….but in two days, that oil soaked in deep. I highly doubt it’s coming clean at all–if it does come clean somehow–please let me know how.
I have a rather large patio in flagstone, with a concrete underlayer. Nicely sloped. I had some bad mortar joints, so I replaced those with chisel and new mortar, and had to replace some stones. It looks good, from a foundational standpoint, but now I am cleaning the excess mortar and finding that many of the stones are also have algae and some spots, so I am trying different methods of cleaning.
Living in a wet and humid climate, the algae will continue to return. I have done the knee pads and wire brush, citrus orange cleaner, experimented with 30% vinegar (I hesitate to go as strong as muriatic acid), and a drum roller that is used to strip paint from cars in grit 40 to 120. I think I am finding the right mix of these to both remove the over application of mortar, and to buff the spots off the flagstone.
I would be interested in your appraisal of my approach, but more importantly, wondering what, if anything, I can do to keep the nice variations in blue and brown and rust and red that I have when I clean, because the stones do not tend to stay that way. I was considering a sealant, but read your views on that, and do not want to go that route.
The only way I ever clean flagstone is the easy way: power washer. Just point the wand at the stones and spray, moving in closer until you see it getting clean. Don’t go any closer than that, and you won’t damage the stones. I don’t know of any way for the stones to stay true to color, especially in a humid or shaded climate. One client used to have that issue and she would just pay me to power wash once every 3 years.