White Limestone Pool Coping - Discoloration & Proper installation methods?

La Dominicana

Member
May 12, 2021
12
Peoria, AZ
Hello all! We recently completed our owner-builder pool/spa in the Phoenix area. I named her "La Dominicana" as the finish selection was inspired by a trip I took to the Dominican Republic. I sourced white limestone/shellstone from one of the larger suppliers here, purchased through a local retailer. The material is 3cm Mayra White/Freska Limestone in a 16x24 for both coping and decking. The stone retailer told me to have the pool coping laid with white thinset in between any mortar bed and the stone to prevent possible seepage of mortar/moisture/color up into the porous stone. I told the decking contractor that (along with many other specifications I requested that were ignored or brushed off until I repeatedly bothered them) but they refused to listen. They laid the coping over the bond beam with a standard grey mortar/thinset mixed combination - no grout joints and no separate layer of thinset. None of the coping was "back buttered" either, though I don't know that would be necessary or standard for a coping install? This contractor is licensed/bonded/insured, but is adamant they've done nothing wrong.

Long story short, the coping vs. decking field is a darker color (we're 3 weeks out from the day it was laid so it's all mostly cured), which I can only assume is from seepage into the stone from the grey mortar/thinset mix. The contractor says "this has never happened before" and blames the stone supplier/quality of the stone for discoloration, says the stone contains more iron and reacted with the mortar/thinset material. They came out and tried putting hydrogen peroxide on it, which I don't think did anything to the color at all. I guess they think it's oxidation, though the color to me doesn't seem rusty/orangy, it seems just "darker" to me. He also says the grout joints are not necessary and that I should not worry about pool coping popping off with this installation method of mortar/thinset mixed together vs. a separate layer of thinset in between mortar bed and the stone in general (whether white or not). Obviously the stone supplier is going to tell me they should've used white thinset to avoid the discoloration...

QUESTIONS:

1) Has anyone had this experience with discoloration of white limestone or other similar when laid directly over grey mortar/thinset?
2) I'm assuming there's little to be done to correct the color vs. ripping it up and having new material laid, but someone PLEASE PLEASE correct me if I'm wrong....?
3) Has anyone had travertine or other natural stone coping laid with mortar/thinset mixed together and nothing else? Any longevity issues?
4) Thoughts on no grout on coping, coupled with no separate thinset layer being used...should I be worried about water seeping into joints and loosening bond with the mortar/thinset mixture over time?

Clearly I'm not a tile/paver/coping installer but I have a few other installers that have "weighed in" and they say always use grout joints and always use thinset, and white in the case of a porous white stone.

ANY ADVICE APPRECIATED!!!!!!!!! And :) Thanks for reading my long post!
 

jamjam

Well-known member
Jun 25, 2020
650
NY
yup we need pictures. A white thinset should not have been an issue for him to use at all - he should have done what you asked even if he thought it unnecessary as it literally has zero impact on him. And yes white would have been what most pros would have used for a porous light colored stone. As far as the joints, well, I would have expected him to have consulted with you on the layout and if you had wanted grout joints. The biggest functional concern you would have is with a freeze thaw cycle, which I assume you don't have to worry about in your area? Having no grout lines is pretty much a subjective decision and many people are going in that direction for a more modern look.

using thinset on the concrete bond beam is the way to go, as long has he got proper coverage and used a modified thinset or mortar bed appropriate for the bed depth (which i am sure he did) you are good to go. I am not a pro but I don't see a need for a separate mortar bed and then a thinset bed unless you are trying to build height.
 
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La Dominicana

Member
May 12, 2021
12
Peoria, AZ
For other background to accompany these photos....I asked for a brick-lay pattern that did not have a change or transition to coping. I wanted a seamless look. At that point, I wish the contractor had presented the grouting vs. no grouting issue, as keeping that pattern there was no reasonable way to have grout joints on the coping pieces without huge sand joints in the field. The mortar/thinset mixture in grey was used to build up underneath the pieces of coping that would otherwise "hang off" the bond beam. I understand now why they did not use grout/grout joints but I still feel there should have been a discussion and some client education involved in a large, expensive job so I could make an educated decision. I also included final photos for funsies, where the issue is less obvious in the lighting. Only pieces that are secured with grey mortar/thinset are dark, anything over the field in sand is still light. There is a slight halo along the field's "edge lock" that was mortared in as well, but it's not hardly noticeable and I'm not necessarily asking the contractor to rip that out...Trying not to be petty.
 

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JamesW

TFP Expert
Mar 2, 2011
27,550
In my opinion, I don’t think that the mortar color is going to bleed through and darken the stone that much.

The stone looks like it is naturally just two different colors.

Did you inspect all of the stone for color for a before and after comparison or was the stone all on pallets where you could only see the top layer of stone?

Maybe the supplier slipped in some darker stone and hid it on the bottom hoping no one would notice?

If all of the stone was put down with the same mortar, the color of all of the stones would be the same.

Also, the color is too consistent for a bleed-through stain.

In my opinion, the contractor should probably have followed the instructions of the stone supplier to use white mortar, just to be safe.

In my opinion, they should have used grout lines for a mortared stone.

Is the deck stone mortared down or just set on sand?

In my opinion, all of the stone should have gone over concrete and have been mortared down with white thinset and they should have used grout lines.

One possibility for the discoloration is if the stonemason was not careful and they used the same bucket of wash water to wipe down the stones.

When doing grout or mortar, you have a bucket of water with a sponge to wipe down excess mortar or grout.

When the mortar is dissolved in the water and then you wipe down a porous stone, the mortar color will stain the stone.

I think that staining from wash down is the most likely cause of the stone discoloration based on how even the discoloration is.

If they had been more careful to only wash down the stones with clean water, the issue probably could have been avoided.

If they had used white mortar, the staining would probably have made the stones a little bit whiter and it would be less noticeable.

Using a white mortar and clean water for wash down would have likely avoided the issue.

It’s always hard to say for sure with stone since it’s a natural product that will have natural variations in color.

Maybe the stones came as two different colors and the stone masons tried to use the darker stones for the coping thinking that it would reduce the problem of having two different colors?

Overall, I can see how you would be disappointed with the final look as you expect it to be perfect for the price you pay.

It’s difficult to say what is fair at this point.

Part of the problem is a lack of clarity in everyone’s expectations of exactly the final result will be.

It’s really up to the contractor to make sure that the expectations of all parties are as clear as possible to avoid problems since they do this all the time and they should know what the issues are.
 

JamesW

TFP Expert
Mar 2, 2011
27,550
I don’t personally like sand set stone because it will begin to shift over time and you end up getting uneven stones with protruding edges that look bad and they are a tripping hazard.

My preferred stone set is all over concrete and set with mortar with properly sized and consistent grout lines.

The deck should be almost perfectly flat and sloped the correct amount.

All of the stones should be examined for color to make sure that they are going to look right for the final look.
 

La Dominicana

Member
May 12, 2021
12
Peoria, AZ
James - Thank you for the input! See my comments in red :)
In my opinion, I don’t think that the mortar color is going to bleed through and darken the stone that much.
See below "test" pieces are pending for comparison. I'll post pictures when the sun comes up here (it's 5am).
The stone looks like it is naturally just two different colors.

Did you inspect all of the stone for color for a before and after comparison or was the stone all on pallets where you could only see the top layer of stone?
Yes, at the yard before delivery and once it was delivered to my home. I watched the entire process, each piece pulled out from crates - I work from home. All pieces were the same color before install.
Maybe the supplier slipped in some darker stone and hid it on the bottom hoping no one would notice?
Nope, saw each piece laid out after cuts made and before mortared in. I even had a few pieces moved off the coping area and swapped out as I knew those coping pieces would be "permanent" vs. the deck pieces over sand that could be swapped out later if I wanted.
If all of the stone was put down with the same mortar, the color of all of the stones would be the same.
Only the stones that have grey mortar/thinset mixture underneath changed color. The pieces over sand in the decking/field are not discolored.
Also, the color is too consistent for a bleed-through stain.
I'm not sure I follow. If the mortar was laid consistently underneath, wouldn't the "seepage" into the porous stone be expected to be complete?
In my opinion, the contractor should probably have followed the instructions of the stone supplier to use white mortar, just to be safe.
Yes, if a supplier and customer both insist on something it should be followed. The total bill for decking/tile (waterline & feature)/coping labor with this company is around $8500 (included the daybed built from cmu) not including any materials. Ripping the coping up, replacing glass waterline tiles that get damaged in the process and having it all redone is ballpark $4200.
In my opinion, they should have used grout lines for a mortared stone.
Had I known it was a good idea and that I wasn't able to get it with the "look" I wanted, I probably would have changed my mind and chose function over form. But none of this was explained RE the grout. I feel the tiny sliver of grout at the edge of the coping isn't going to keep the sand locked in very long.
Is the deck stone mortared down or just set on sand?
Sand.
In my opinion, all of the stone should have gone over concrete and have been mortared down with white thinset and they should have used grout lines.
Here in AZ, the sand set method for the deck is industry standard. I spoke with 9 PBs before deciding to go owner-builder and I believe that all would have used sand set for the field with a mortared edge only.
One possibility for the discoloration is if the stonemason was not careful and they used the same bucket of wash water to wipe down the stones.
Could also be part of the problem yes. I've lost confidence in the mason (see below).
When doing grout or mortar, you have a bucket of water with a sponge to wipe down excess mortar or grout.

When the mortar is dissolved in the water and then you wipe down a porous stone, the mortar color will stain the stone.

I think that staining from wash down is the most likely cause of the stone discoloration based on how even the discoloration is.

If they had been more careful to only wash down the stones with clean water, the issue probably could have been avoided.

If they had used white mortar, the staining would probably have made the stones a little bit whiter and it would be less noticeable.

Using a white mortar and clean water for wash down would have likely avoided the issue.

It’s always hard to say for sure with stone since it’s a natural product that will have natural variations in color.

Maybe the stones came as two different colors and the stone masons tried to use the darker stones for the coping thinking that it would reduce the problem of having two different colors?

Overall, I can see how you would be disappointed with the final look as you expect it to be perfect for the price you pay.

It’s difficult to say what is fair at this point.
I insisted they have the mason install two test pieces side by side, one the same method they used for the coping (we even had them build a small concrete pad to simulate BB beneath) and the second piece with a layer of white thinset between stone and mortar bed. The mason came and tried to do this by mixing white thinset powder INTO the regular grey mortar mix....CLEARLY they are not understanding the concept that the white layer of thinset is to help keep any seepage white as to not stain the stone. I had to explain to the guy how to do this test right (layering vs. mixing it in).....Anyway....They are still drying and curing so it's too soon to make a final conclusion, but I'm already seeing the darker color show up on the test piece without the white thinset layer while the one with white thinset layer is remaining light....I'm virtually certain the supplier was right and I was right that white thinset would have helped prevent the problem. I asked repeatedly for them to use it.
Part of the problem is a lack of clarity in everyone’s expectations of exactly the final result will be.
I think it's pretty clear that having ~70 pieces of stone stained on a white paver job isn't acceptable to any homeowner...Especially when their specific request would have prevented the issue (test results tentative but that certainly seems to be the case).
It’s really up to the contractor to make sure that the expectations of all parties are as clear as possible to avoid problems since they do this all the time and they should know what the issues are.
 

La Dominicana

Member
May 12, 2021
12
Peoria, AZ
yup we need pictures. A white thinset should not have been an issue for him to use at all - he should have done what you asked even if he thought it unnecessary as it literally has zero impact on him. And yes white would have been what most pros would have used for a porous light colored stone. As far as the joints, well, I would have expected him to have consulted with you on the layout and if you had wanted grout joints. The biggest functional concern you would have is with a freeze thaw cycle, which I assume you don't have to worry about in your area? Having no grout lines is pretty much a subjective decision and many people are going in that direction for a more modern look.

using thinset on the concrete bond beam is the way to go, as long has he got proper coverage and used a modified thinset or mortar bed appropriate for the bed depth (which i am sure he did) you are good to go. I am not a pro but I don't see a need for a separate mortar bed and then a thinset bed unless you are trying to build height.
Thanks jamjam :) I don't think freeze/thaw is a big concern here as we very rarely hit freezing temps. I really do think the white thinset layer would have prevented the discoloration. We have a test going right now and it's looking like the white thinset piece is going to remain lighter while the one laid the method they used is darkening. They were laid yesterday. The contractor was saying during our meeting that if the test "went my way" then we'd still get someone from the contractor board to weigh in and he believes they would say that it was not a workmanship issue even still....I think he's trying to strong arm me into just paying him.
 

jamjam

Well-known member
Jun 25, 2020
650
NY
if you asked for a seamless look between the coping and the patio with an integrated layout, then i don't think the contractor owed you any further education as I would assume you would understand that the coping would have no grout lines just as the patio. But i can see how it maybe didn't really come up in your mind. A really good contractor would have made sure every detail was covered.

I guess it is up to your test, now. It does look like it is a different batch of stone to me, but I will take at face value that you are confident that it isn't.

are these two stones i highlighted in your picture mortared down?

20210408_174011.jpg
 
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JamesW

TFP Expert
Mar 2, 2011
27,550
Since you checked the stones beforehand and they were fine, it would seem that the contractor is probably responsible for the discoloration.

Hopefully, the test stones will provide some more insight.

I suspect that the stones were washed down with water that had been used for cleaning up mortar and that is what caused the discoloration.

If you remove the stones, you could cut one in half to see if the color goes all the way through.
 

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jamjam

Well-known member
Jun 25, 2020
650
NY
is it possible that the stones that are affixed are holding on to moisture differently than the stones sitting in sand?
 

JamesW

TFP Expert
Mar 2, 2011
27,550
I would have done a mortared and grouted 12 X 24 coping, which would allow for the stones behind the coping to be set in sand with no problems.

That's how it is usually done.

In my opinion, a concrete base and mortared stone with grout lines is a much better way to set stones for the deck.

I don't like the sand set method.

To me it looks much less sophisticated and professional than a mortared and grouted set.
 

JamesW

TFP Expert
Mar 2, 2011
27,550
If it is just surface staining, you might be able to fix it by sanding, but the look of the stone will change.

Probably worth a try if you're going to replace the stone anyway.
 

La Dominicana

Member
May 12, 2021
12
Peoria, AZ
if you asked for a seamless look between the coping and the patio with an integrated layout, then i don't think the contractor owed you any further education as I would assume you would understand that the coping would have no grout lines just as the patio. But i can see how it maybe didn't really come up in your mind. A really good contractor would have made sure every detail was covered.

I guess it is up to your test, now. It does look like it is a different batch of stone to me, but I will take at face value that you are confident that it isn't.

are these two stones i highlighted in your picture mortared down?

View attachment 332576
Yes, those two pieces are fully mortared - because they are partially over BB, the rest that "hung off" the BB was backfilled with extra mortar mixture to build up height. Again, I even see a slight halo around the edge that is mortared to lock the field. I promise I inspected these stones every day, multiple times a day before, during and after they were laid. They were pulled randomly from the various pallets vs. just one as well.
 

La Dominicana

Member
May 12, 2021
12
Peoria, AZ
is it possible that the stones that are affixed are holding on to moisture differently than the stones sitting in sand?
That was definitely one theory in the mix, this has been laid since 4/1. It's been 90s and broke a hundred a few times recently. We gave it 4 weeks of curing to see if it was moisture before I told the contractor I was doing a retention until we get it hashed out.
 

La Dominicana

Member
May 12, 2021
12
Peoria, AZ
Since you checked the stones beforehand and they were fine, it would seem that the contractor is probably responsible for the discoloration.

Hopefully, the test stones will provide some more insight.

I suspect that the stones were washed down with water that had been used for cleaning up mortar and that is what caused the discoloration.

If you remove the stones, you could cut one in half to see if the color goes all the way through.
I am going to run some tests on the wipe down theory, you could be right! Had the last item been white thinset, the sponge wouldn't have been dirty or as dirty with mortar water. I didn't see a separate clean water bucket being carried around. They wiped as they set each piece and then later washed it all down with water, I think at the end of the day when all pieces had been laid....I'm in a bit of a state of stress and didn't consider that as the primary cause initially. But, it could also make more sense given that pieces all around the daybed that is built from mortar/block and then stuccoed, those pieces are also discolored. They wiped that area down as well. I think I'll try wiping an extra piece down with a dirty mortar sponge and see what happens before I try sanding a piece that's set or ripping it up to cut it in half. I saved some of their trash to make sure I know which products they were using so Ill buy same.
 

jimmythegreek

TFP Expert
Bronze Supporter
In The Industry
Aug 10, 2017
3,847
Morris Cnty NJ
The thinset color will not bleed up thru, I've never seen it. White thinset is actually more expensive and slightly stronger to the equivalent grey thinset, and on premium brands can be harder to find. On material like this James is right on the money. The whole assembly should be laid on the same fashion. Sand bedded material will hold moisture differently than mortared material amd will change the shade unevenly. With coping, the manufacturer will never use the same batch as the field, so you have 2 different stones even though they are the same material. That's why it is required to lay from different pallets and batches as you go to offset any variations. It's a natural product and can vary. The only way to get some solid results is to run a test panel. Use leftover pieces and thinset then down both coping and field amd see what variations if any turn up. I like the look and pattern alot, but I would have advised you to keep the coping amd field in a seperate pattern for this very reason. Natural stones can do this amd with a seperate pattern you wouldnt notice the zippered effect as much. It's a clean nice look, not a roll of the dice with stone. Hope you get a resolution that works out for you
 

JamesW

TFP Expert
Mar 2, 2011
27,550
In my opinion, mortar will not bleed through a good, hard, dense stone.

Washdown with dirty mortar water most likely stained the stone.

Sanding might help depending on how deep the stain goes.

Sanding will be difficult to do and retain a good surface.
 

jimmythegreek

TFP Expert
Bronze Supporter
In The Industry
Aug 10, 2017
3,847
Morris Cnty NJ
There are good stone cleaners out there but some will damage the finish on certain stone. Need test pieces. I still think its just the stone being from 2 different lots
 

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