Salt deteriorating grotto top slab?

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grottoguy

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Aug 24, 2014
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NJ
My pool was built last year and there is a Grotto made out of rock. My contractor didn't have one solid bluestone slab that fit the top so he put on two pieces (one of which covered most of the Grotto). He cemented the two pieces together. You can see the cement in the picture. IMG_3544.jpg. I noticed water seeping through last year so he redid the cement. That stopped the problem until this summer when I noticed water seeping through and more importantly, I saw that the top of the Grotto (when inside) was flaking and little pieces were coming off. Pictures below. IMG_3548.jpgIMG_3551.JPGIMG_3554.jpg

My contractor showed up and immediately told me he's never seen this before and it must be my SWG and I had to get rid of it immediately. He then told me the salt was affecting the structural integrity of the Grotto and although it would be fine for many years, after 15 years or so there could be a problem. I told him my Salt was 3000 PPM and even without a SWG it would likely be at 1000 PPM (I learned that from this cite - I hope correct) and I didn't want to get rid of the SWG. He then said after some thinking that he could clean the flaking and try sealing the top (on both sides) and that I should do it every other year. He also suggested that I have him seal the Moss rocks on top of the Grotto and the Moss rocks inside the Grotto. He proposes using a natural look non-color enhancing sealer. He would also redo the joint between the 2 Bluestone slabs. He wants $1200.

Questions:

1. Is the salt causing the top of the inside of grotto to flake? It seems to be happening where the water was coming through the seem as well as near the opening (perhaps when the water comes down the falls it gets pushed back a little inside). But it also is flaking in the middle of the top as well. Interestingly, on the other side of the top (where I can walk on it), I see no Flaking at all (although maybe the constant water flow would wash evidence of that away?)

2. If I seal it (and that seems to make sense to me), do I need to do the Moss rocks on top of the Grotto and inside the Grotto?


Thanks everyone
 
The problem is, how to prove it one way or the other....

Personally, I believe it is just water in general and the particular type of stone.

I'd see what else could be done to prevent water from going through the seam, and I'd see if the PB could grind a 1/4' groove on the underside of the stone, right up near where the water comes over the edge. this would act like stop to prevent water from flowing back along the bottom of the bluestone.

Jim R.
 
This subject, stone and salt, is beaten to death on a regular basis. I apologize if I sound design cynical.

A pool builder will always blame anything they can on salt, water chemistry, or anything else to get out of warranty work if they are not a stand up company who stands behind their work. Salt is a common scapegoat. I have flagstone around my pool that everyone says will disintegrate before my eyes if I use salt. Yet, they look exactly the same as they did 5 seasons ago. Unsealed, never rinsed and frequently never rained on for months at a time. I have some flagstone in a path away from my pool that is deteriorating a fair amount. How can that happen without salt? Can stone really deteriorate if there isn't a saltwater pool splashing on it? Egads!

Stone is a natural product. Even stone from the same field will have different characteristics. Which is why some folks like stone better than concrete. Because it looks natural. Some stone flakes. I have some that flakes and some that doesn't. Some flakes more than others.

So, is the PB really expected to warranty a 27 million year old rock against flaking? I don't know. It doesn't seem like it is something they can control. I often wonder about grottos like yours and how safe a natural slab of stone is. How often do they break? A neighbor had a stone slab like that going across a little stream, maybe 5-6 feet across and 3 feet wide, and it broke smooth in half when somebody stepped on it once. I would prefer reinforced concrete myself.
 
Agreed with other comments above.

I have a natural stone waterfall composed of a lot of different types of rocks from the Catalina mountains (the waterfall sub sources his stones very locally....pretty much anything he can haul behind his truck. Lots of different beautiful colors and textures. Some of the stones have beds of mica and garnet buried in the matrix. There's also some beautiful red colors as well.

Guess what? The waterfall "sheds" grit and particles all year long. Not a lot, but it all lands on the swim out shelf. I vacuum up maybe a small palm-full of tiny bits of rock and sand. I once found a really neat 1/2"x1/2" piece of mica that my kids had fun peeling apart into the microscopic sheets. Is all this caused by my salt water? Nope. It's all pretty much mechanical wear from the waterfall.

My guess is that some of that blistering and flaking is just the natural action of water penetrating a porous surface (bluestone is porous) and remaining trapped in there. The underside of your grotto is constantly bombarded by the humidity of the water below it so it is always wet. This chunk of stone, formed millions of year ago, probably spent most of that time burned in the ground seeing very little water or moisture. It is now being constantly bombarded by water and taking that water deep into it's sub-structure. As that water goes through heating and cooling cycles, the internal microscopic mechanical forces can cause fracturing along crystalline habit planes which leads to macroscopic spalling. It's completely natural.

Sadly I have to say that your chunk of blue stone there is doomed....it's probably only got a few hundred thousand years to go before it completely deteriorates ;)

Personally I would not seal the stone. But you might find a way to make that motor joint more resilient. You could have him beef up the mortar joint or redo it possibly with an epoxy based mortar that will resist water penetration. Or, if he wants to retain the traditional mortar used there, you could consider sealing the mortar and the surround joint to keep water out. Just a thought.
 
Matt,

When you say you would not seal the stone ( but would seal the joint), is that because you don't think sealing the whole stone will do much. I assume you don't think it would cause a problem?
 
grottoguy said:
Matt,

When you say you would not seal the stone ( but would seal the joint), is that because you don't think sealing the whole stone will do much. I assume you don't think it would cause a problem?
Click to expand...

I'm just saying that piece of stone forged in the depths of the Earth for millions of years is going to last longer than the mortar that Giuseppe mixed up in his wheelbarrow. The mortar is more likely to be susceptible to water damage than the rock so I'd look to seal that. The stone can be sealed too, I just don't think it's worth the hassle.
 
JoyfulNoise said:
I'm just saying that piece of stone forged in the depths of the Earth for millions of years is going to last longer than the mortar that Giuseppe mixed up in his wheelbarrow. The mortar is more likely to be susceptible to water damage than the rock so I'd look to seal that. The stone can be sealed too, I just don't think it's worth the hassle.
Click to expand...
That darn Giuseppe can't mix mortar worth a darn! :p
 
I'm going to agree with Matt and Dave. Stone is a natural product, predicting its behavior is not all that easy. Like Matt I have residue that comes off my waterfall, Maybe in 50 years we will see a difference. My Mortar has changed color and shrunk just as the PB predicted. The Mortar will probably show more deterioration. I also don't like the fact that the underside of the grotto has the water exposure. That means the mortar seams are constantly at a higher humididyand may be leaching whatever faster than if they were dry.
 
Thanks everyone. I didn't think it was the salt either. I think I'll ask him to redo the morta joint and seal it as well. I might have him seal both sides of the Bluestone cover as well (seems like it can't hurt) but not the rocks on the top or inside the Grotto.

Matt you mentioned having a water resistant epoxy for the mortar. Is there any particular one I should suggest? Is there any particular sealer?

Thanks
 

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Update; I asked my Grotto builder to fix the joint connecting the two bluestone slabs and he quoted me $900 to fix the joint, clean the flaking (which will take 2 minutes by just rubbing it off ) and seal the top and bottom of the slab (with a Stonetech water-resistant sealer). I thought that this should be his responsibility because when he cemented the two slabs together, it leaked right away, and then after he fixed it, it only lasted one summer. But I wasn't interested in a fight so I was willing to pay it if he would warranty the work for three years so that if water leaked through again he would fix it. He likes to claim that having two roof slabs joined together is my fault because when he first brought one slab we rejected it - because it was barely hanging on one edge over the Grotto. His General contractor kept rotating it, but even his GC was not comfortable with the slab (and told us so).

His response to my request:

"I had proposed to install the roof of the grotto as one piece to prevent the joint issue and we had a well-suited piece sitting on top of the grotto. You and your wife were adamant about the 2 pieces. I can not extend the warranty on this – after this repair, it won’t be covered. I think it was too hot when it was done last time, so the concrete cured too quickly."

My reply: "That is not fair. The one piece you proposed was not good. You're own contractor didn't like it and suggested we deny it. He told us and our landscaper. My wife and I should not be obligated to accept a roof slab that appeared unsafe to both us and your own contractor. You had ample opportunity to get another piece and came back with two pieces. We gave you all the time you wanted to find a suitable slab. In your expert opinion you indicated two pieces would work. They did not. It failed immediately and had to be redone within weeks after you joined them together. And after it was redone it failed again. It obviously at a minimum should have been sealed initially. And now you are making me pay to fix this mistake. The flaking and deterioration is NOT due to the salt. It is due to the moisture which is being aggravated by the weakened joint. The amount of salt in my pool is not much more than the amount in most non SWG pools using liquid bleach and there is no scientific evidence that the small discrepancy in salt is the cause of this problem.

Frankly, I don't think I should be paying for this at all. In saying after this repair you are not extending the warranty, you are implying that this is under warranty. Yet you are charging me a lot of money for labor to fix a problem with the construction. You even say the failure is likely to it being done while it was too hot. I am being more than generous by agreeing to help you cover your costs (frankly much more than your costs) with this, but I would like a three year warranty on the water seeping through the sealed joint. With all due respect, if redoing the sealed joint with a sealer can't stop the seapage for at least three years, than this method should never have been employed. Please reconsider your position. It's not fair. "


His response: "I'll guarantee the repair for 2 years if you switch from salt. If you continue to run salt over the stone, I won't warranty it. We use bluestone for spa spillways, coping and waterfalls with no issue...ever...from the moisture. The only time that we see degradation of the bluestone is when a salt system is involved. Anthony Sylvan pools had sent failing stone out to a lab from one of their own employee's pools and salt was determined to be the cause...which is why they won't install a salt system without a waiver. The fact that there is more flaking by the end of the stone by the spillway, shows that it has nothing to do with stone leaking into the joint. My foreman was telling you what you wanted to hear on the slabs. The first slab was perfectly safe...running the salt system is not. "

Although he knew we would have a SWG when he was doing the job, he did suggest we consider using liquid Chlorine.

Forgetting about the flaking, is it likely that the salt could be causing the seapage? It seems to me he NEVER should have used two slabs on my roof if he wasn't comfortable that it would hold up. But what do you think? I'd like an unbiased opinion before I decide my next course of action. How would you respond to his claims?

Thanks everyone. I am anxious to get your thoughts.
 
Sorry, I saw this yesterday and wanted to respond but had a busy day...

Well, this is just my opinion, but I think you've entered the phase that most pool owners eventually arrive at - your PB really doesn't want to deal with your pool anymore. Warranty work, no matter what trade you're in, is a money-loser. You have to send guys out and materials and it's just a total waste of time especially if you're busy building other pools. The responses from your PB indicate that he's really done with you and your pool and will be willing to do the most minimal repair job with no guarantees. In my opinion, this is how most PB's operate.

As for the salt/no-salt stone debate, you can't win it. He's going to point to his Anthony Sylvan data (is that his company or some other major PB?) as proof that "I told you so!" and you can make all of the logical arguments you want and they will amount to nothing in his mind. Honestly speaking, I think it's just the constant moisture load on the stone both from the humidity below and the water flow above, along with temperature cycling for your climate (freeze/thaw cycles) that is causing the stone to spall. I don't think there's much that can be done about it unless it is sealed.

As for your option, well, I can only think of two. Either accept his offer to fix the grout joint (which seems way over priced to me at $900) OR find a reputable stone mason in your area and get their opinion on what to do. Honestly one piece of stone as opposed to two pieces mortared together is the better way to go, but I'm not sure what a stone mason in your area would charge for remodeling of that grotto slab...it could be a lot more than $900.

Sorry you're going through this, it sucks. I had a small, hairline crack develop in the PebbleTek plaster surface in my spa (about 8" long) and I have been waiting since May for the plasterer to put me on his schedule. I call every month and it's a different excuse every time - too busy with pool builds right now, it's too hot to do the work, I only want to send out my best guys (blowing smoke up my rear), etc, etc. This is just how the warranty game is played for pools, most PBs simply want your last check form the build and then never hear from you again...
 
Thanks Matt. He does some work for A&S when they recommend him but they were not my pool builder. I actually learned about him when I interviewed A&S so ended up using him solely for the grotto and rock wall. I think the two pieces of stone cost him about $1500 or so ( I was able to price it out at time by calling his supplier) and changing it out would be very expensive (I bet at least $3500 if I was lucky ) cause it would require a lot of things. What annoys me is that if he isn't willing to guarantee that the mortar joint won't leak for three years, then he should never have used two pieces in the first place.

I would have paid his ridiculous $900 if he would have guaranteed his work. And I only asked him to guarantee that the water wouldn't seep through- he didn't have to guarantee the flaking. I am getting another quote and will consider suing him for costs to fix it because I don't like his attitude. It won't cost me anything in legal fees and would give me satisfaction.

I know you don't think the salt is causing the flaking, but do you think the salt is causing the mortar joint to fail?
 
grottoguy said:
I know you don't think the salt is causing the flaking, but do you think the salt is causing the mortar joint to fail?
Click to expand...

Yes, this is very likely BUT it depends a lot on how the mortar was mixed and what specific type of mortar was used. Standard masonry mortar (the kind you use in brick laying) can be very susceptible to salt-attack. But it depends a lot on environmental conditions as well, such as duration of exposure, evaporation, relative humidity, etc. Here is an excellent article from the Australian Government Dept of Environment on the role of salt-attack in masonry structures -

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&ved=0ahUKEwiwhsPZ4OzOAhVHOSYKHeuaBAMQFghaMAk&url=http%3A%2F%2Fwww.environment.sa.gov.au%2Ffiles%2Fsharedassets%2Fpublic%2Fheritage%2Fsaltdamp_techguide.pdf&usg=AFQjCNElD0DBIkP49gI91JJmD516WC-AOQ&sig2=ZCDiwAgg8hdDtnXDK2ZeSQ&bvm=bv.131286987,d.eWE

I think the mortar joint needs to be pointed (tooled out and refilled) or completely redone with a bonding material that can resist water permeation. pooldv's suggestion of using a waterproof polyurethane caulk might work, but you need to ensure that water cannot find a path to the mortar around the caulk.

I look forward to seeing what other information you can get from the other quote. That's a nice piece of bluestone, too bad the rest of the grotto was not designed to fit it better. It's a very thick piece too, I wonder that, if you just let it be, will the spalling eventually stop?
 
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