Slate pool coping is disintegrating. Opinions please

luckynumber7December 21, 2010


We have slate coping and waterline tile installed in our gunnite saltwater pool which was built about 2 years ago. A number of the bullnosed coping tile are eroding and spalling chunks of slate/mud into the pool. The waterline tiles have fared much better and have only mild signs of erosion.

I suspect that the pool builder did not seal the tile properly and that this is caused by the electrolytic nature of a saltwater system. The most affected tiles are in the shallow end of the pool where the evaporation rate is higher. Overall, I'd say that I plan to seal the tiles over the holiday with a product called DryTreat 40 SK which is supposed to impregnate and strengthen friable stone. Then I'll try to repair the worst 3-4 coping tiles later. We live in houston so I don't think freeze & thaw is an issue.

Any opinions on weather or not this is a worthwile endeavor? The sealant is pricey. Or is it better to just let it play out for another season and get quotes for what will likey be a pricey remodel affair?



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Post a pic so we can see.


    Bookmark   December 21, 2010 at 5:07PM
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Here are photos. First is of a tile that is in relatively original condition.

The second is one fairly eroded. Note that this is worst where the water has a high rate of evaporation. we have a raised wall with cuppers that rarely get used and these are in pristine condition. The outer edge of our raised spa and fire pit have the same coping. Also with no issues.

    Bookmark   December 22, 2010 at 3:36PM
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I'd say you're right about it not having been sealed. Looks like the stone selected is a bit porous and not particularly hard. Heat from the sun followed by the splashing of cooler water created temp changes and caused the layers to separate.

How have you been testing the water balance?


    Bookmark   December 22, 2010 at 5:07PM
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Been testing the the water balance using chemical drops 1-2 times per week. Occaisionally I'll take a sample in, but I've been disappointed by inconsistant results I get from them.

I used to run an aqueous geochemistry lab in college, so I'm fairly confident in my test results.

I've been running my PH around 7.5 and alkalinity between 90-100. I also
pay a lot of attention to the power I supply to the Chlorine generator. I try
to keep the chlorine level ~2 ppm. I try to manage scaling pretty religiously
since we have a dark pool bottom.

I agree with you on the hardness aspect of these stones. The darker tiles are harder with lower clay content and are clearly holding up better. I'm hoping the impregnator will add some strength while lowering the permeability. At thispoint I just want to arrest the erosion. I think the pool actually looks more natural than it did originally, so that's not much of an issue. That will change if it gets much worse.

    Bookmark   December 22, 2010 at 6:30PM
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WRT your Free Chlorine level, use the following chart:

Effective FC levels are based on your stabilizer (CYA) level.

A drop test kit such as the Taylor 2006K or TF-100, which use DPD-FAS tests for chlorine levels can test to 50 ppm by going from pink to clear will tell you exactly where your level is and when the combined chlorine level needs to be shocked out.


    Bookmark   December 22, 2010 at 7:17PM
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Like you said, I think it looks very natural at this stage. Hopefully, you can stop it at this stage. Have you tried an Anode?

    Bookmark   December 23, 2010 at 8:11AM
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We also live in Houston and had our pool built about 2 years ago. We used slate on the coping but regular tile on th water line. We haven't had any trouble at all. But there is some more to the story. My builder has had trouble with slate in the past and really didn't recommend it but my wife LOVED it. He agreed to talk to the local stone providers about it (forget their name at the moment...) and they said that during the time my builder had his issues, there were a lot of complaints about slate coming from particular areas of India. They checked records and found that the troubles were with the same slate my builder had used in earlier jobs. They said that the slate they had in stock had not seen the same issues, so we went ahead with it. We did seal it however with a pretty pricey sealant. We've had some VERY minor flakes come off the surface (not the bullnose end though) which is typical of slate, but overall they look brand new, and we do have a salt system. I do keep my chemicals in check fairly religiously as well. So, not very helpful, but thought I'd mention it...

    Bookmark   December 28, 2010 at 8:19PM
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To the OP we have an outdoor summer kitchen and it is covered in slate. I used a product to seal it called Sealers Gold choice made by Aqua Mix. It is a professional sealer for all types of stone including slate. It is not cheap however it seems to make the slate harder and definitely repels water and moisture. I think I paid about $105 for a gallon. All reviews seemed great. Hope this helps.....

    Bookmark   December 30, 2010 at 8:05AM
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Thanks for your help everyone. My Drytreat order shipped today, so I'll let you know how it works out.

On a separate note, I also got the dreaded "Salt cell no power" error on my control panel this weekend. Opened it up to find that one of the fuses completely melted and burned the circuit board. Thank god that's still under warranty!

    Bookmark   January 3, 2011 at 8:23PM
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The coping looks like a sedimentary stone which is layered. I don't think the chemicals are causing it, rather the natural freeze thaw-actually more of a expansion/contraction process in your location. Sealing the water out is the way to go..My salt system quit working when the water temp got down to 55F. I called the manufacturer to ask if the low temps had caused this- He said YES, and that is normal. I took the salt generator out for the winter and replaced it with a "dummy" for the winter to increase it's service life. (about $40) I have an Intellichlor and unless you are heating the pool for winter use it is not really neccesary to run the generator all year long. Rather than draining the system I decided to use the timer to run it on low during the times when hard freeze is expected. (Piedmont of NC)

    Bookmark   January 4, 2011 at 10:25AM
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Hi All,

I am also near Houston, and thinking about having a pool installed with natural slate coping. My husbands brother who lives in AZ swears by his salt water chlorinating system. I'm not so sure, having no experience with this, just with typical fresh water chlorination.

Any opinions as to pros and cons? I'm trying to get the ducks in a row before gathering estimates.

Thank you all in advance :-)

    Bookmark   October 14, 2012 at 4:57PM
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