Stone vs. SWG dilemma in Texas?

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Thanks for the great info everyone! I'm glad to see there is some discussion going on here.

Hal3, love your pool. Your blanco stone looks just like our existing limestone. Do you know which stone yard it came from? How is it holding up to salt water and how long have you had this combo? Do you think it's limestone or some other stone?

Maybe others can comment on something I was told at one local stone yard. They said the farther north the sandstone comes from (ie: Oklahoma vs. Arizona vs. Mexico) the harder and more resistant to salt it is. This would lead me to think that Mexican sandstone would be softer since it comes from even farther south? I don't know about this. Has anyone else heard this before? We're still planning to use the Mexican sandstone at this point.
 
I think if you ask your supplier about "Blanco Stone" he will know what you mean or call a stone place in Austin.
It is much harder than sandstone. Sandstone will be easier to cut and shape into a square or rectangle based layout with a smoother surface. Since the Blanco Stone is more like stone it is usually laid in an irregular pattern like you see.

I have zero problems with the salt on the stone after about two years. My stone was placed about ten years ago, though, and I think it hardens or something after it is exposed and used. It has a rogh surface that is smooth enough for the feet but definitely non-slip. I have not noticed any corrosion on the stainless parts but they are about 20 years old and not too shiny to begin with.

I will never go without SWG again. If you look at my first posts on this board you will see that I have progressed from a standard chlorine puck based pool that was impossible to maintain to, after all the great help on this board, a SWG pool that I would never have to touch except for removing leaves from the bottom and the skimmers. My chemistry stays perfect all the time with no effort.
 
Thanks for the stone suggestion Hal3 and for your PM. I'm going to call some local stone yards tomorrow and see if they carry it. I haven't seen it anywhere on my previous visits to stone yards. I wonder if it's a limestone? Glad you've had such good luck with it!
 
Is there any reason high ph would accelerate the recrystallization process? I have seen the same stone hold up in SWG pools for several years but started deteriorating in less than 3 months on a new installation when the swg went unchecked and sent the ph past 8.4. The deterioration was very fine particles similar to DE when brushed, not nearly the density of sand.
 
I, too, have seen the salt erosion with my own eyes. I good friend of mine had a pool built that, within the first year, had severe erosion of the stone coping.
The coping had to be replaced and the pool was converted to a "chemical" pool.

When we were entertaining builders to build our pool; not one, said they would install a SWG. "Too many problems" was always their answer.

If I was the OP and wanted stone I would just install a liquidator chlorine feeder and be done with it. I don't know if borates would attack stone like regular salts but they can be added to give the "soft feel" like a SWG pool.
 
carolina pool said:
Is there any reason high ph would accelerate the recrystallization process? I have seen the same stone hold up in SWG pools for several years but started deteriorating in less than 3 months on a new installation when the swg went unchecked and sent the ph past 8.4. The deterioration was very fine particles similar to DE when brushed, not nearly the density of sand.
Click to expand...
This paper talks about salt recrystallization pressure, but there is no mention of pH being a factor. However, they did not look at salts whose precipitation would vary with pH. That is, they did not look at calcium carbonate. I'm guessing that at high pH one might get more recrystallization from calcium carbonate. When the pH is lower, carbon dioxide leaves the system and makes the pH rise, but that means there are less carbonates to form crystals. When the pH is already higher (some of which may come from chlorine gas outgassing from the SWG which raises the pH without lowering the total carbonate level), more carbonate can remain to form crystals. This is just speculation on my part.
 
I love my SWG,and would never have a pool without one. But, the pool was designed as a salt pool with no natural stone. As far as calcification of the unit in hard water areas, all that is needed is to closely monitor the CSI. I keep close tabs on my TA and pH levels to keep the saturation index at or slightly below zero, and I haven't had to even clean the unit in the past year.
 
Thanks Richard, I was hoping to get a response from you. The referenced article is a little over my head.

This stone is Tennessee sandstone and it doesn't react when muriatic acid is poured on it which leads me to believe there is little or no calcium carbonate in the stone. I had not considered the calcium level (250) of the pool water and whether that would factor in? There is no current evidence or fracturing or of the sedimentary layers separating. It almost appears as if the color is being removed from the stone and the sediment is extremely fine.
 
When I referred to calcium carbonate, I meant in the splash-out water and that it could re-crystallize. No calcium carbonate would be needed in the stone itself. The splash-out has salts that get into cracks in the stone (or more directly in porous stone), get over-saturated as evaporation occurs, then crystallize which puts pressure on the stone.

As for the coloring changing and fine sediment rather than fracturing, then perhaps that's an effect caused more directly by high pH, but I don't know the mechanism.
 
FWIW, my SWG is almost two years old and I've had no issues with my travertine coping. I sealed it with a good sealer and I'll re-seal it again this year. In long dry spells I also will wash down the coping with fresh water once a week or so. So far so good.
 

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Thank you chem geek for trying.

It wasn't my intention to reopen the pro/con issue of salt and should have started a new thread. This instance and a few others of runaway ph seem to be more damaging and I thought there might be a relationship. We have had success with swcgs and similar stone.
 
[This paper talks about salt recrystallization pressure, but there is no mention of pH being a factor. However, they did not look at salts whose precipitation would vary with pH. That is, they did not look at calcium carbonate. I'm guessing that at high pH one might get more recrystallization from calcium carbonate. When the pH is lower, carbon dioxide leaves the system and makes the pH rise, but that means there are less carbonates to form crystals. When the pH is already higher (some of which may come from chlorine gas outgassing from the SWG which raises the pH without lowering the total carbonate level), more carbonate can remain to form crystals. This is just speculation on my part.[/quote]

Okay, I have read the above a few times and am trying to grasp it.

This is my real life experience and perception of calcium carbonate recrystalliztion,
1. Stalactites in limestone caves or the difficult to clean scale near water features, etc
2. The way plaster seems to seal itself upon resaturation after its dried out and checked.

1. seems to occur under a lack of pressure.
2. there must be some level of pressure,

Are you saying that #2 is potentially happening in the coping mentioned?

If thats the case wouldn't there be a noticable reaction to muriatic acid? (I have not tried this since the deterioration started)

Richard, I know you are shaking your head and thinking "how do I explain this to a pool builder" so please bear with me give it your best shot.

Thanks, Rod
 
Yes, if there was calcium carbonate getting into the stone, then adding acid would have it bubble, but there might not be very much of it. For deterioration of the stone, it's about salts of various sorts (sodium chloride, magnesium sulfate, calcium carbonate) in water that evaporates and the formation of the salt expands. Think of ice forming that expands when it forms, though technically the way this works is a bit different.

The thing is that you aren't reporting cracking. So instead it might be that higher pH reacts with the stone's coloring to cause it to dislodge as fine particles, sort of like paint stripping, but again, this is just a guess and I don't really know.
 
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