Should You Seal Your Stone Patio? Ask Devin

           Devin Devine, stone mason based in Pennsylvania, projects across the [email protected]

UPDATED summer 2025

Sealing a flagstone patio

I keep receiving comments on my blog about sealing flagstone, and the question keeps coming up during DIY consultations, so I figured this would make a good edition of “Ask Devin”. Do you have a DIY hardscape project such as a flagstone patio? Feeling like you could use some professional guidance? DIY hardscape consultation services available!   TL writes:

Hi Devin, I live in north east Ohio and came across your website when I was researching flagstone patios. I did not see any comments or suggestions on your website regarding sealing flagstone, so I thought I would send you an email . My wife and I bought some flagstone from a local supplier a few years ago to build a patio. The flagstone was gray and orange in color and had a really nice patterns.

We are not experts in laying flagstone, so we hired a landscaping company to install the flagstone for us and provide expert advice. He suggested using polymeric sand between the stones, and also recommended putting a sealer on the patio that would protect the stone, and also give it a “wet” look.

They did the work in late fall. Laid the stones, filled in the spaces with the polymeric sand, and then sealed the whole patio. They were most of the way complete, and just needed to come back in the spring to install the edging and put a final coat of sealant on the patio. Since we personally knew the landscaper, we paid him in full for the project, and expected him to come back in the spring to do the final steps.

When spring came and all the snow was melted, we went outside to see how the patio looked. To our horror, the stones were ruined.

The nice patterns and colors that the stones had were all peeling off. Therefore we contacted the landscaper, and his immediate response was that we had “bad” stone. I never heard of such an expression. How can stones be bad? The landscaper never provided any further explanation of what “bad” stone was. He was supposed to come back and pull up the stones, so we can get them replaced, and then was going to lay a new patio for us (without sealing it).

To make a long story shorter, he never came back out. I ended up pulling all the stone up, and putting in a new patio all by myself. The landscaper told us that he filed a claim with his supplier and that we would get a full refund due to the sealer being no good. Do you have any experiences like this?

Can a sealer destroy the color and look of flagstone? Attached are a few pictures we took after we found the stones ruined. In some pictures you can even see that the landscaper did not do a good job cleaning off the stones before sealing them, since the polymeric sand is sealed on the stone in some areas.

I would love to hear your thoughts and experience in this area, and if you agree that our conclusions make sense. The sealer was no good and/or the landscaper did not properly clean off the sand before sealing the stone. Thanks!

  Sealing flagstone is not recommended.

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With any grade-level masonry, if you seal the top, then you potentially trap in moisture.

Water can still get into the stone through the bottom of the stone, but now it has no way to evaporate, because the top is sealed. Polymeric sand is not the best thing to use with flagstone, either. Looking at the photos you sent me…..there’s spaces between them flagstones that look a good 10″ wide. I guess he decided to put a little bit of flagstone in-between the polymeric sand.

As a professional, I have not sealed a flagstone in many years, for reasons of not wanting to trap in moisture. The old answer, that I always used to give is “do not seal flagstone…..but if you really must insist on sealing it, then use a matte finish. A glossy finished product is more likely to create a slippery surface”.

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As for the allegedly “breathable” sealants available now:

Even if your product is *actually* breathable….and *actually does both–keeps water out while not trapping water in….   –even of it does both these things(at the same time? THINK, the fact is that bluestone does not need to be sealed. If a thing is unnecessary, then doing it is a mistake, and may well cause unforeseen problems down the line.   To avoid flagstones flaking–inspect them before installing. Stones that will be prone to flaking up will tell you.

Tools needed to build your stone patio on a gravel base:

• 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.
• GRABO, 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.

Related articles, DIY and hardscape how-to:

• what to use for under flagstones, concrete, sand, gravel, or what?
• what to put between your flagstones sand, mortar, polymeric sand…..or stone dust?
• how to manage weeds on your stone patio
• replacing the cement between flagstones, re-pointing
• how to clean your flagstone patio
• DIY hardscape consultation services–professional guidance on “how to build your own flagstone patio”
• how to build a dry stone wall
• how to cut flagstone with a hammer
• Grabo vacuum lifting tool review
• CHECK OUT my stone art (and share on your social media) too!

UPDATE

Based on a conversation had below, in the comments, I’ve come across this product on amazon. The product claims to be:

• Water repellent characteristics help to reduce deterioration caused by water absorption and freeze-thaw cycles
• Will last for up to 3-5 years before the need to reseal
• Breathable, low VOC, single coat application.

So this is what I mean when I say “do not seal flagstone….but if you do, then use something matte”. This product claims to be breathable–that’s the key word. What we’re being led to believe here is that the product will repel water from entering stone, but it does not create a water-proof film and all-importantly, that it does BREATH. If it breaths, then moisture (allegedly) won’t get trapped.

I’m still cautious and skeptical on the matter. Chances are I won’t be using this product myself, any time soon, preferring to keep things as natural as possible,

Not a professional installation. These wide gaps might be acceptable if you had some sort of gravel in between the flagstones….and if the job were being done by a home owner (or a landscaper). With gaps that wide your polymeric sand is guaranteed to crack. The manufacturer may claim that their poly-sand is good for gaps up to 2″ wide. Again and again however I see that that is not the case. 6″ to 10″ wide gaps? No way.

    I recommend:

• 6″ of compacted roadbase type gravel (3/4″ minus crushed stone)
• Stone dust (1/8″ minus, or 1/4″ minus) as both leveling agent and joint filler

 

Effects of sealing flagstone

stone peeling up, don’t seal flagstone

  Flagstones are usually sedimentary stone, that is built up in layers. The layers are often different colors…   It seems that what happened is the stones absorbed groundwater from below, and could not evaporate. Then freeze-thaw came along, and that moisture that was trapped just below the stone’s surface went and froze, causing the topmost layer to flake up, peel off, delaminate, or spall. Hence, the beautiful colors of your flagstone were ruined.

But you also asked “can stones be bad”?

(I do not believe that this is what happened to your flagstones, but to be complete I’ll have to include this final paragraph)

Stone quality may vary. For one flagstone walkway, that I built a decade ago, the stones that we purchased had visible cracks along their edge. Like a book, flagstone is (often) built up in layers. If you look at the edge of the stone, you may be able to detect these layers….well, for this one project, our stone showed up, and a good half of the stones had obvious faults–if you looked at the edge of the stone, it looked like the “book” was starting to open up. An inch and a half stone was looking ready to be peeled apart, with a visible seam somewhere in the middle. So I had to purchase tones of extra stone, and got rid of most of the old, faulty stone. But ultimately, we had to use what was available. Got rid of the worst, kept the best, bought in some new stuff and got it done.

The problem came next spring, and I had to return to replace a few (might have been 8 or more) flaked up stones. Lesson learned!       And that was a bummer! The stones weren’t flaking up in paper-thin layers like yours did, rather they were cracking in the middle, so the top 1/2″ of a stone would peel off. I learned a painful lesson….having already purchased twice the amount of stone as the job originally called for, I then had to return a year later and work for free for a day. Worse still, 2 years after that the customer called again. This time it was only 2 or 3 stones. This was a decade ago and happily, none of my walkways have had trouble like that since then and going forward I know: don’t risk laying a stone that looks like it’s ready to peel apart.

Final word on sealing flagstone

So I’m sorry this happened to you and your patio! I can’t say for absolute certain that the sealant is what caused this failure. But it is not recommended to seal flagstone– and if a flagstone did fail because of sealing…then your photos are exactly what I would expect the failure to look like. Paper-thin layers, peeling up.

Good luck with your new stone patio!  

consultation services

…..this is the perfect time to tackle that DIY flagstone/hardscape/dry stone wall project that you’ve been dreaming about doing on your own. But where to start? Wouldn’t it be totally awesome if a professional with over 23 years experience in this field was available to guide you, and talk you through the entire process, answering any site specific questions you may have? The response has been overwhelmingly positive. Email [email protected]