Devin Devine, flagstone contractor, mason and sculptor
based out of the Poconos, Pennsylvania
devin@devineescapes.com
DIY hardscape consultation services available
Flagstone Repair Explained: wet laid flagstone
This article shall go into some detail, explaining how to repair flagstone, how to assess flagstone damage and maybe some ideas about flagstone repair cost
Flagstone repair can be a tricky matter, and confusing for the home-owner. Especially in the case of wet-laid flagstone, flagstone patios and walkways that have been laid in a bed or mortar. This article shall hopefully explain the issues at play and make it easier for home owners to find the right contractor for the job.
Flagstones that are set in cement can be vulnerable to heaving due to freeze-thaw conditions. Here in Pennsylvania we have serious winters, leading to serious winter damage to masonry. (HINT if you’re having a new patio installed go dry-laid. repairs for dry laid will be much simpler.)
flagstone repair: BEFORE
flagstone repair: AFTER
Some important questions:
- how old is the patio or walkway?
- how long have the flagstones been showing damage–cracked mortar joints, loose flagstones?
- have you, the home owner observed these conditions worsening over the years?
- if there are major cracks present, how wide are they–and have they gotten wider over the years?
- Check references and ask to see a portfolio of completed works
That last question is one you should ask the contractor. The rest are questions that your contractor should probably be asking YOU.
For this flagstone repair job every single stone was taken up. Foundation was repaired and stones re-set. Many of the original stones were deemed too thin/not likely to last too many Pennsylvania winters–and so they were replaced with thicker stones.
The last couple of questions relate to trying to discern if the problems at play involve and serious foundational issues or not. That question is best answered by having a professional mason pull up a couple stones and have a look. Still, I’ll always ask, as it’s good to know how the patio or walkway has behaved over the past few years.
I used to do these types of jobs for an hourly rate, since you can’t accurately predict exactly what a repair job will take. Not so, anymore! I find that I can look at a damaged or aged patio, judge fairly well what the job will take, and just give a full quote for the entire job. I used to bill 90 an hour for me, 40 an hour for a helper–now I just decide that the job will take 3 days and xxx amount of material, and quote you at that number.
General plan of action for Flagstone repair | how-to repair wet-laid flagstone patio:
I’ll now describe a hypothetical flagstone patio which is in need of repair and then I shall outline the proper means of repairing said damage. Problems–failing mortar joints between flagstones on many or most flagstones. Some of the flagstones are lose. A long crack exists on one section of the patio, running over ten feet long which is fairly clear indication that the foundation itself has some serious cracking.
Solution:
Loose flagstones shall be removed. Old cement from underneath these flagstones shall likewise be removed.
Any crack in the foundation itself shall be widened to a full inch in width. Widened crack shall be coated with a masonry adhesive agent, this shall be given proper time to set up. The crack should then be filled with proper mortar mix with bonding agent added to this mortar mix as well.
New steel* reinforcements may be added as well, along the crack area.
*or basalt
Often flagstones that have come loose have a) to deep of a mortar bed and/or a very thin flagstone was used to begin with. If such is the case…and in my experience it often is, then I will a) use a thicker flagstone thus ensuring a smaller mortar bed and/or b) fiber additives will be added to the mortar mix. These are 1″ fiberglass strips, they look kind of like shredded up cigarette filters and are sold as a stucco additive. Mortar has a low structural integrity. Concrete is stronger, by comparison, because it has gravel added to it. The addition of the fibers will strengthen the mortar, making it less likely to crack.
This video will hopefully be of some help, to illustrate some of what I’m talking about:
Many masons will build patios with thinner stones and thicker mortar beds, because it saves them money, gets the job done quicker, is much easier, and is likely to last very well….for a few years or so. A proper mortar bed for flagstone should be about one inch in depth, say half an inch to one and a half inches. Very often, more often that not, really, when doing flagstone repairs, I find flagstones that were laid in a solid two inches, or even three inches of mortar. Yikes, not good. Mortar is the weak link, and should be kept to a minimum. Irregular (natural shaped) flagstone is sold by weight, thus it is much cheaper to use thinner pieces. Being lighter in weight, it is also easier and faster to install thinner flagstone. Furthermore, a two inch thick bed of mortar is a faster installation technique–you can just slop a whole bunch or mortar down and then take your individual flagstones and smoosh them down to the proper level. Your individual flagstones are of various thickness, thus having a deeper mortar bed will make it easier to get them all down to the same level.
The above paragraph merely describes one of the common cut-corners in flagstone installation. Stuff that I see all the time. Masons and landscapers follow such practices because a) the home owners do not know any better and b) sometimes the workers do not know any better. I hope this article serves to educate both my fellow stone masons as well as to better arm the savvy home owner and protect them from unscrupulous or unskilled contractors.
I prefer thicker flagstones. They have more mass and thus are less easy to disturb, to come loose, or to heave from the freeze-thaw. It’s harder to dislodge something that is heavier. Common-sense, right? Seriously, there are masons out there who have not figured this out yet. What? Masons everywhere–read Devin’s blog, and take notes.
Thicker flagstones are also more well-rooted. A two inch flagstone will have 2 inches of mortar along it’s sides, wedging it down in better. Commonly, masons and hardscapers will recommend thicker flagstone for dry-laid work and will proclaim that the thinner stuff is fine for cemented-in work. In the short term, yes. Mortar however is not infinitely tough stuff and it is weaker than stone. Have more stone down there, less cement. Okay? My approach to wet-laid work is informed by 17 years experience in this trade and by many years experience performing repairs and many years doing dry laid work. Grade-level )ground level) masonry is vulnerable. My wet-laid work is informed by my knowledge of dry stone work. Thicker flagstones are more steady for dry stone….that means they’ll be more steady for wet-laid work too.
In summary:
- Find and repair the foundational cracks
- re-set flagstones in no more than one and a half inches of mortar mix
- don’t use too-wet of a mix.hire someone who you believe will take their time and will pay attention. This stuff is not rocket science…paying full attention, having many years experience and actually caring about the work they do–these are the qualities to look for when hiring a masonry repair service.
- More how-to articles related to flagstone work: patio and weeds and what to use, sand cement or gravel? Also, for those of you interested polymeric sand, I’ve written up an article weighing the pros and cons of polymeric sand as compared to stone dust.
Also, please check out the gallery pages for more examples of my landscape/hardscape work, patio ideas and dry stone sculpture….in fact, if you find my advice helpful, you should say thank by sharing some of my artistic dry stone work on whatever social media you use.
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We have a flagstone patio in the Boston area that is in need of repair. I have built dry set patios before, but never wet set. This patio dates back to the 1970’s and I’m not even sure that the stones were wet set. There seems to be a mix of sand and concrete underneath. Many stones are loose and mortar joints have failed. It’s in tough shape. Can I remove all existing concrete joints and simply use stone dust? Or would I be better off sticking with concrete in joints?
I’d go with stone dust. It seems the original flagstone installation probably involved a dry laid patio with cemented joints and maybe some cement beneath. ..this is considered a poor practice. Cement is rigid–you do not want to use a thin amount of rigid cement over a foundation of sand/gravel. The joints will just crack up.
Possibly the original work had a proper foundation and over the years cement has broken down and crumbled…wet laid patios do not do so well as far north as Boston. In any event, I’d go with stone dust. I cannot promise that this will stabilize loose stones for you. For dry laid flagstone you want your stones well set unto the bedding sand/stone dust/whatever, of course. But you also want to use flagstones that are a good inch and a half thick or thicker. Wet laid patios and poorly done dry laid patios, often use thinner stone.
Good luck! And if you appreciatey advice, please share some of my photos and/or articles on whatever social media you use. Thank you 🙂
Devin- I think you’re spot on with your diagnosis. There’s an inch of old concrete then about 3 in of sand beneath that and then it appears to be concrete beneath that.. .however, most of the stone is an inch or less thick. It’s a about a 900 sq ft area. Any further suggestions?
Thank you very much for your response, will share with folks up this way
Well, as you know, for an inch or less thick, I’d prefer to see it wet laid.
For broader stones, I can often get the stone wobble free, even if it is only an inch thick. But the broader you get, at that thin, the more flimsy the stone may be…in your case, any flimsy stones have already broken.
It might be a case where you can buy some new stone, and throw out the thinnest and smallest of the old stuff, then re-lay dry.
Some times, your best bet is to call in a pro. Not saying you can’t do it yourself….just saying that a lot of pros would find your situation challenging. Well, most pros these days are selling you on faux stones and pavers–flagstone work is not super easy.
To me, the job basically sounds like a complete re-build, or at least a near total re-do.
The good news is, I think you generally have a decent grasp of the situation. And My blog has an entire how-to section, with a few more articles exploring how to go about laying flagstone. Hopefully, I have a least been of help, and I wish you luck!
I had a total redo of my flagstone patio 2-3 years ago .flagstones set in concrete.Used old where possible..a few stones are slightly lower or not properly graded. A couple have imperfections. I have a few puddles well after the rain what can I do. Is there s filler?
If you have puddles on a mortared patio… Then them stones were not laid properly. I have no short cut to offer: them stones need to be re-laid, properly this time.
Best of luck. (Find a good mason and confirm via his portfolio that he knows how to do this type of work. Look for online testimonials, and ask for references)
We have a brick colonial in NJ which has roughly 12 x 5 foot flagstone raised patio in the front. Its is raised about 3 feet in the front increasing to about 5-6 feet in the rear.
We’ve had it rebult twice in 20 years as it collects a lot of snow and water. Since its raised and has always been wet fitted should we consider dry fit with stone dust?
The current stones are in good shape but shifted up or pushed down due to the extreme winter we just got through. I would welcome your thoughts on how we should go about getting this repaired correctly.
Thank you
For dry fit, you want the stone to be thick enough that it will stay steady underfoot. generally, an inch and a half should do it. Generally. The way the stones are fit, and how much surface area will both play a role in determining stability, but inch and a half is a good rule of thumb. For wet laid jobs, I often see an entire patio with every single stone an inch thick or less, sometimes averaging as thin as only half an inch. Such thin stones, I would not dry lay.
I’d consider doing a better repair than the previous guys did. No offense to the other masons, but I have my own technique is all–partially outlined in the article above. My repair would likely involve replacing some stones with thicker ones.
I can’t say too much more, without a more clear idea of what your situation is. You said “raised”. What type of walls is is raised upon? Are the support walls in good shape?
We have extensive walkways and patios of wet-laid flagstone in the front and rear of our house in southern Ontario. The flagstone ranges between 2″ and 2 1/2″ thick, and was laid on a poured concrete base. The mortar joints have cracked in most areas and there has been a significant amount of breaking off of pieces of stone beside the joints. The adjacent Indiana limestone coping around our pool has shifted enough to break the underlying mortar joint for each stone. The flagstone is domestic Wireton flagstone. The upper surface is “flamed” (as I understand it, saw cut and then flamed to cause pieces to flake off and provide texture). Most pieces have a natural rough under-surface, although there are some pieces that have a saw-cut under-surface.
We have had two stone masons look at the stone. One blames the mortar mix for failing, saying that the mortar must not have been mixed properly (not enough Portland cement or another additive). The other mason, who took up a few areas of stone, blames the stone itself, which in most cases had fractured horizontally so that the bottom half or third of each stone separated when lifted. The bottom of some of the stones was sandy clay I.e. Not hard. The latter mason thinks frost got into the seams in the stone and caused heaving, which broke otherwise sound mortar joints (exacerbated by water penetration and freezing). Our original installer simply denies all responsibility.
We expected the job to last far more than 5 years, and expected that only occasional spot re-pointing would be required from time to time, or a full re-pointing after perhaps 25 years. obviously we are disappointed with the prospect of having to completely remove and replace all of the stone after less than five years.
Do you have any suggestions? Thank you in advance.
Too cold of a climate for grade level cement work.
Flagstone should be laid dry, when in a northern climate.
The amount of failure you describe sounds like it’s a bit much, for 5 years, I’ll grant you. However, sight unseen, I can not say much more. If you want a more in depth opinion from me, then you can email me photos of the job and request a phone consultation:
https://www.devineescapes.com/diy-flagstone-help/
Again, whenever anyone wants me to install flagstone for them, I insist on doing dry laid. There’s just too much freeze-thaw around here.
Best of luck and sorry you’re going through this!
I’m trying to reset step flagstones, but part of the stone rests beneath stackstone. Is it possible to remove the flagstone and temporarily “shim” the stackstone so it does not collapse?
I’m sure that it is possible–if you try your best and don’t get frustrated too easily by it. Dry laid steps can be tricky.
What you describe is a careful maneuver. Use a stone of similar thickness to the flagstone that you are removing, and slide it in place of the flagstone….fast and smooth-like. Might work. You’ll certainly disturb the stacked stone a bit and so the next step up from the one you are working on and so it will need to be tweaked a bit too. Have a good mallet and a decent pry tool handy.
That’s a bout all I can offer. If you want to send me photos and have me walk you through the process then we could do a phone/email consultation.
Good luck!
I am having my front walk redone (they began today). I am in the same climate as you I think (living just north of NYC. They are removing all concrete between the stones. They are not going to reset the stones that are firm in place. They will use a water and cement mixture to set the lose ones. The concrete they fill in will be about two inches deep. Is this good enough, or what should I tell them?
I appreciate being able to ask for your advice. BTW, I have a lot of social media and will share your website.
You should always hire the most qualified contractor. One who you do not need to second guess like this. If you do find a proper stone mason please never dare to tell them how to do their job. Respect a professional.
But if you can’t find that sort of artisan, a true gentleman with dirt under his nails, then you can always come to https://www.devineescapes.com and ask me. I am here to help.
If they are re-setting loose stones, then they should be using a mixture of portland cement, sand and water. Not just cement and water. Type S is what I usually go with. Pre-mixed stuff is fine.
The material in between the flagstone is probably not concrete–it is probably cement based mortar, like what they are using to re-set the loose stones with. Concrete, is a different mix–one that has larger aggregate–gravel.
2 inches deep? You mean between the flagstone joints? Between the joints, you’d usually remove and replace whatever is loose. No need to grind out/chisel out any deeper. 2 inches deep then…..is that’s how thick the stones are/how deep the cement mortar is. Half an inch or deeper is fine.
Hopefully, that answers your questions and sets you at ease. If you want more specific answers then that, then you can email me photos of the project and we can set up a phone consultation.
Good luck!
What should I do to remove mold from the grout between flagstones? Also, what sealer is best for preventing it returning? I would really like to use a sealer/paint combination in a “brick” color that would solve the mold problem once and for all. (I don’t suppose there’s a mold remover/sealer/paint that would be all-in-one application?)
Thank you very much for your help.
Pressure washer. Any natural look/non-gloss type of masonry sealant. You do not want a gloss product because they can make your flagstones slick and slippery.
Sealer/paint combo in a brick color….? Nothing I can recommend.
Good luck though 🙂
Hello, I just came across your site while doing a search on flagstone. We had our patio installed late fall of 2014. The flagstone walkway has been chipping or peeling considerably since then. Is this common? Or did the contractor use something else in place of flagstone like shale? I would appreciate any feedback. Thank you!
I really couldn’t tell you…I’d need to see a photo. If you put up a photo on imgur and post it here, I might be able to tell.
Thanks so much for your response! Here are some images – the first two are the flagstone patio. These are not chipping and I’m wondering if it’s because its on a covered patio and laid in concrete? The other images are the walkway area that I’m concerned about. Not a covered area and I don’t remember what was used but it wasn’t concrete.
http://imgur.com/a/mFYg7
Hello, I live in souther Colorado and have flagstone steps that have lifted off the concrete base. The flagstone is 2″ thick. What would you suggest to repair this?
Thank You!
Flagstone walkway is discolored with moss growing between them. How can I make it look nice again. Will I need to pull them out and reset them?
You shouldn’t need to lift your walkway stones up, just to clean them. A power washer is probably your best bet. Usually, any flagstone can handle a power washer, but start out carefully and slow, to make sure that only small bits, if any, of actual flagstone is coming off.
Would like to ask a few questions regarding a job that was done out here on the West Coast very unique application for flagstone on a floating home in Sausalito California. The job looks absolutely perfect however unfortunately for some reason this deck has begun to leak water into the living space below. The substrate was originally 2 x 6 tongue and groove and on top of that three-quarter inch plywood was screwed and then a roll-on membrane called Deck 70 Buy universal protective coatings was put in place which is a very tough roll-on membrane used to waterproof in our area on top of that a mortar bed was placed and wet set flagstone Quartzsite.
Q- How to best remove the pieces of quartzite without breaking them so they can be reset after we re-waterproof the substrate material.
Q- suggested best elastomeric membrane that could be used to create the waterproof barrier on top of the wooden membrane made of 2 x 6 tongue and groove and three-quarter inch plywood
Use 4″ angle grinder with diamond blade to remove mortar in between stones. Use hammer and chisel to pop the stones loose–hold the chisel almost flat, and get up underneath the stones. Depending on stone type, you may not need to remove move of the mortar in0between the stones–usually a single dive-cut into the mortar joint is enough. You should be able to get the stones up with maybe 20% of them breaking–and most of the broken stones will hopefully be large enough to re-use. Be ready to purchase a small amount of new stones, but really I don’t expect much trouble there.
I’d look into a liquid applied membrane. If I was choosing to go with a roll on membrane, then I’d have a bucket of liquid membrane on hand as well, to use in potential problem areas, like where different planes meet up, wall meets floor, etc.
My guess is that the roll on membrane was punctured somewhere–or the leak is coming from a bad seam. Membrane should be properly overlapped and, like I said, I’d take special care wherever the floor becomes complex, corners, change of pitch, etc.
And pitch is important too. Usually, I’m going with 1″ of fall, for every 4′ of span–or 2.5″ over 20′
Numbers given are approximate, but I’m usually not less than 2″ of fall and not more than 3″
This is steep enough (on solid land applications) to let water run off of the flagstone surface, but it still feels level. Also, the plane needs to be fairly consistent. Natural stone is often imperfectly flat, but you still don’t want any real dips in the surface. If water can puddle anywhere, then it may soak through the mortar and then find a way through the membrane too.
20$ per sq ft to have me do the work–lodging, material and flight provided.
devin@devineescapes.com Send me photos and measurements, if interested.
We live in Maryland and had a flagstone patio powerwashed. They left marks from getting too close to the stone, like shadow graffiti almost. Is there any good remedy? Is powerwashing again just going to do more damage? It is a brand new patio, flagstone is more than 1″ thick. Thanks!
Power washing should not damage Flagstone, so power washing it again will not do more damage so long as they don’t get too close to the stone.
If you’re in Maryland, then there is a good chance that the flagstone you’re talking about is Pennsylvania Bluestone. If that is the case then someone with the skill might be able to fix it using an oxygen acetylene torch. This it’s the same type of torts second to use to cut steel with.
Spilled bbq grease on flagstone. Gone all summer so it really soaked in. Tried power washing and bleach, not helping. Any suggestions?
Yea, I’m not sure how deep the oil may have soaked in. Hitting the stone with an oxygen acetylene torch with a blue flame will cause thermal spalling of the surface of many types of flagstone (bluestone, sand stone, granite, others). You dampen the stone, then hit it with the flame, and a thin layer of stone pops off. This might, maybe work if the grease was somewhat solid and didn’t soak in too deep. I’d probably go over the spot with an angle grinder and a diamond blade and plane down the stained area, removing about an 1/8th inch, maybe 3/16ths of stone surface, then dampen the area with water and go over it with the torch. The torch will remover another 1/32 inch of stone, and leave a more natural-looking than surface (the grinder will leave the stone surface looking obviously tooled). So long as the stain is only an 1/th of an inch or so deep, maybe a quarter in at the deepest, than this method should work. Many types of stone are quite porous so I don’t know….good luck and let me know if it goes.
My place is in northwestern MA hills (Ashfield) and I’m madly trying to repair my flagstone steps before it’s too cold. They are not wobbly but much of the mortar is missing likely partly from the supposedly “concrete safe “ ice melt I used last year and whatever others used for same purpose before. I figured I could re-mortar the gaps with small stones to bolster large gaps. I have cleaned as much as I can reach without weakening whatever is back there (and has been for 30 years). I have a bonding agent and a mortar mix I planned to add a bit of acrylic to as recommended by the mason supply place. Does this sound like a good idea? Should I try to make some kind of vent maybe with straws to allow for expansion/contraction or is this just a kooky idea of mine? PS I will not be using anything but sand this winter for non slipping.
No expansion joint in the middle of a mortar joint needed. No, that’s not kooky! Kidding, yea some people might call that kooky. Cleaning the joint is important. I understand that if it’s old masonry, the more you dig the more loose stuff your going to break up and pull out. So ok stop digging/cleaning, if you’re already a couple/few inches deep, but then do make sure to sponge off the insides of the joint/the edges of the stone you’re re-pointing. You want the mortar to have something dust-free and dry/slightly (slightly!) damp for the mortar to adhere too. If you do use additive, I wouldn’t use much. Mix up your mortar dryer than you think and press firm into the joint. Fall is a good time of year for this work, it’s good for mortar to cure when it’s not too cold or too hot.
Hi Devin,
Do you have a blog that address how to repair dry-laid flagstone patio? Curious about what the DIY steps are for dry-laid flagstone when there are loose stones. Thanks!
Loose stones in a dry laid patio–I take it to mean that you have wobbly stones, that pop up when stepped upon.
1. Lift the stone out of its place.
2. level out the stone dust where it was, as needed. The stone may not be perfectly flat on the bottom….so it may need more stone dust on one side, less on another. Adjust accordingly and then place the stone back where it goes.
3. Check its level, in relation to the stones next to it. Might need to lift the stone again, and re-adjust the leveling material (stone dust). If the stone happens to be only slightly too high, like an 1/8″ of an inch or so, then you can persuade the stone to settle down a bit, using a dead blow type mallet.
https://en.wikipedia.org/wiki/Dead_blow_hammer
4. Check for wobble: put your weight on the stone, leaning on to it, corner to corner (I’m on the ground, wearing knee pads when I do this, leaning my weight unto the stone with my hands). If you push down on a corner and that corner sinks, while the opposite corner rise up–then you know the corner that sank need more stone dust. At this point, you can probably just lift one side of the stone up, rather than removing the entire thing all the way out, and then toss a handfull of stone dust under the stone, at the corner that needs it. Often I’ll intentionally add just a bit more than I think it needs…then mallet it down into place.
As you can see, steps 3 and 4 may involve a bit of back and forth, Just take your time, and don’t over do it with the mallet. Well, if the stone is a good 3″ thick, then yea, you can malet away and pound it into place. If the stone is only an inch and a half or less, then tap it down more gently, otherwise you may break the stone.
5. Repeat, correcting wobble for every stone on your patio of walkway. As a pro, I never have a patio truly 100% wobble-free at this point. I check each stone, on my knees, and get them each seeming wobble-free, but then when I get up and walk around, I’ll notice maybe one or two stones will have a (minor) wobble underfoot. So maybe the patio is about 85% wobble free at this point. The next step will help with that.
6. Refill and top off all joints, with new stone dust. Sweep off the excess, then hose down. Top off joints that settled during hosing….sweep off again. When I’m down, joints are just shy of being flush with the top of the stones. You don’t want to leave joints over-filled, as the material will be all over the stone surface, and will be a bit of a mess. Now, that the joints are filled, the flagstones are looking more like 93% wobble-free. Minor wobbles–no stone should actually pop loose, when stepped upon.
Minor wobbles that still remain at this point are only noticeable if you’re looking for them. Quit looking for them. Over the next 6 months or so, the stones joints will settle in, harden up a bit and when I re-visit the job site 6 months or a year later, they’re just about always approximately 100% wobble free.
WOW–that response turned out longer than I expected. I almost answered simply “throw some stone dust under there”! But since the response was so long already….I decided to add some photos and extra details–and turned the answer into a new blog post:
https://www.devineescapes.com/leveling-dry-laid-flagstones-how-to/
Hi, Devin. We are having a flagstone patio repaired. The inside of the patio buts up against a stone wall. The stones needing repair are on the outside. But when the contractor started pulling up some of the stones, he says the inside stones are not fully set (although they appear to be). We aren’t prepared for the cost of replacing the entire patio. Question: will repairing the outside cause increased deterioration of the inside stones? Bottom line – are we wasting our money?
Mary, Hello. Unfortunately it’s impossible for me to say, without seeing it. If you want we can do an email/phone consultation. But I’ll need a real good look at it–if you can send photos and video from every angle, I should be able to give you an answer that I can be confident about.
Hi. We have a flagstone walkway and steps that was repaired 14 years ago. Many (or most) of the stones are now loose and the grout between the stones is coming out. We have had three contractors give us quotes. A few said they would repair the loose stones and replace the grout (one said he would seal the grout). Another said we should take up all of the stones and redo it all. One also said that the mortar bed on the steps is too think and he would replace the flagstone pieces that goes up the steps with taller pieces. Could you please advise me on what is best? Thanks.
If most of the stones are lose, then taking up all the stones and redoing it all sounds right. I’d need to do a full consult, see photos and video to say much more…a thick mortar bed is something I’d want to look at too, and might agree with the guy about the step. Then again, is the step in good condition still, after 14 years?
I have a wet laid bluestone patio and walkway in the Kansas City area (i.e. temperatures 110F to -10F). The stone was laid wet with mortar on top of a pre-sloped concrete pad back in 2004 or so. The stone itself is generally about 3/4 inch thick. I have gone for most of that 20 years without any significant failure or maintenance.
I finally had a failure that I think actually resulted from a repair. Last fall I cleaned out some broken grout. This was obviously near the seam between an existing patio pad and the poured concrete substrate so that there was relative movement wasn’t a surprise.
The surprise I had next spring was that the stones along the seam had “tented”. My best guess is that I did the previous repair at the end of summer when the ground was dry and shrunken. In the spring the ground regained moisture and closed the crack between the sidewalk and the pad. With the new grout in place there was no place for the stones to move except for “up”.
I just removed the affected stones. The bed for most of those is still in place. I will have to replace one stone that was more of a mudstone and just decomposed over the last 20 years. Plus it was a thinner stone so the bed is of course higher than the rest.
In the last 20 years there’s no way that heat expansion hasn’t broken adhesion with all of the base and then surely water gets under there and freezes. What holds those stones in place normally. Is it just the grout that keeps it from moving and the 3D effect of the bed?
What’s the best way to dig out mortar that was under a stone?
Pardon my delay.
The way that i remove mortar that was a a flagstone depends on the condition of the mortar. Can I get a brick chisel under there and just separate it from the concrete? If not< then I'm cutting tabs with the ANGLE grinder and popping them out with a chisel. If the mortar is rock solid, and at THE right height--I'll use PL loctite https://amzn.to/45x2c8x and just glue the stone back down. Been doing this move for well over a decade, never had a call back, never had one pop back out.
Mortared flagstones are held in place by a) good mortar adhesion to the bottom of the stone b) by the mortar between the stones. Thicker stone are also held in place partly by their gravity and if it is just the mortar JOINT holding it in place then a one inch or inch and a half flagstone will have more grip than a three quarter or half inch stone.
I’m slow in replying too! I already made the repair shortly after my first comment and did pretty much what you said. I used an angle grinder to make a perimeter cut and then cut up a corner enough that I could get pieces to pop and chisel separate the mortar from the concrete. Then setting the stone was mostly pulled out of 20 year old memory.
I cut the mortar out bigger than the replacement stone so I set the stones around it in their original beds but had to put fresh mortar under the edge nearest the replacement stone. I did most of the stones around the new (thicker) stone so that I was having to skim a little mortar out to get the height right.
Forgot how much I hate the cleaning when I do the grout.
Basically, over 20 years I’ve had three kinds of failures. I’ve had two stones that decomposed on me over about 1700 sq ft. That was bad selection. I’ve had a few edge stones where I’ve run over them with the lawn mower or something. Since they are only mortared on 3 sides they move (especially since I seem to have selected smooth stones on the bottom that don’t re-orient themselves). The third, and by far the most common failure, is in the grouting. When I laid the stone I left too high a margin the first summer I did the patio. I was also mixing my mortar instead of using pre-mix. The stones are generally held well by the margin, but the grout is too thin and it breaks (probably due to heat expansion). As I’ve been repairing I’ve been grinding out that margin so that the grout has more depth and that’s seems to be wearing well.
I guess this one was a fourth type of failure where my substrates weren’t connected and I got what appears to be expansion of clay soil after a previous re-grout. I really only have one spot where that can happen so I guess if I have to repair it again… do it in the spring. I can handle a crack better than a tent.
Devin, I had someone build my flagstone patio for me, but over time it has degraded and the outside perimeter, in particular, has sunk due to irrigation, rain and snow here in Colorado. The perimeter was built on top of a clay soil with no base rock using large brick like stones (3″x6″x20″) to help hold up the edges given the differences in grade. Between the perimeter, they tamped the soil and placed granite dust over the top of the soil which was also, somewhat, tamped. On top of all of this is the flag stone which was filled with a very bad polymeric sand which lasted about one year, and an adhesive on the perimeter which did not hold up at all.
I would like to repair it vs. replacing and was wondering the best way to shore up the perimeter, flatten out the flag stone, and fill with a stronger polymeric sand (ie Easy Joint) and secure the perimeter.
Your thoughts or recommendations would be highly appreciated.
Dan, yes polymeric sand is usually used like this–in place of good stone work, to fill in and make up for short cuts. The stone sank because of poor foundation. Somewhat tamped. Granite dust. You want a solid 8″ + of 1″ gravel with fines as your foundation. Stone dust is used as the leveling agent and joint filler. No “better brand” of polymeric sand will make up for the fact that the foundation is lacking. Neither do I ever recommend any brand of polymeric sand in any application, ever.
You want to read one of my overviews, there’s a couple on this website, explaining the entire process for building dry set patios. Might also want a look at my article on dry stone wall building.
If you still need advice, then we should set up a consultation and you should send me photos.