Do Salt Generators damage limestone/masonary

3 year old 18,000 gallon gunite/plaster pool with aquarite generator. I have a leuters limestone coping that is crumbling away, breaking down with little fissures and a general deterioration of the stone. Builder says chlorine generator caused it, because it manufacures bleach, which breaks down masonary products. I also have been using bleach to supplement the generator, and to shock the pool when needed. Has anybody heard of anything like this? I am replacing the coping, and he is adamant that i get rid of the salt water system.

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Originally Posted by craiga

Builder says chlorine generator caused it, because it manufacures bleach, which breaks down masonary products.

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LOL.........and what does he want you to use?? Chlorine :eek: Sorry I can't answer your ? on the SWG. I'm just curious on what he wants you to use in your pool, if your "manufacturing bleach."

craiga,

It's very interesting that we are only now starting to see complaints of corrosion in SWG pools on this forum, but when it rains it pours. Look at this post for an example of very fast corrosion of stainless steel in an indoor pool with an SWG, but also not using any CYA. I have also started a controversial and technical thread here in The China Shop to try and understand what is going on (if anything, since this may be a general corrosion issue not related solely to SWG).

Unfortunately, we don't have definitive and absolute answers to this, but what can be generally said is that higher disinfecting chlorine (i.e. hypochlorous acid, HOCl) levels are more corrosive (as would any strong oxidizer), that higher salt levels (i.e. salinity) and/or higher conductivity are more corrosive, that acidic conditions (i.e. low pH) are more corrosive (even high pH can be corrosive, too), higher dissolved oxygen levels (oxygen is an oxidizer) are more corrosive, having dissimilar metals touching is very corrosive to them (due to galvanic corrosion), having high water flow rates is more corrosive (due to physical corrosion), etc.

[EDIT] The previous discussion about factors influencing corrosion are about corrosion of METAL, typically iron, steel (including stainless steel) and copper. Corrosion of stone surfaces probably does not have some of these factors such as galvanic corrosion so may not be affected as much by conductivity. However, the other factors are still relevant as most stone resellers will tell you not to use acid around some stones (even acid from juices such as lemon), to be careful of oxidants (including chlorine bleach) and to avoid salty environments (especially heavily salty environments such as by the ocean). Remember that plaster/gunite/grout can be corroded "dissolved" just by plain water alone (water is sometimes called "the universal solvent") and requires calcium carbonate to be saturated in the water. So every type of stone, cement or other coping/hardscape surface is probably a little different in its susceptibility to corrosion and what makes it corrode faster. Also different stones have different abilities to be sealed and therefore protected from water and different sealants have different susceptibility to oxidants. I'm sorry I don't have definitive answers for you, but at least by asking the right questions we can get ourselves on the right track. The only personal experience I have with the sensitivity to stone is with our travertine shower where after less than a year we started seeing darker shading to the stone and smelled mildew. It turned out that our stone installer used a cheap sealant that only lasts 6 months. We dried out and re-sealed with a high-quality sealant that should last 3 years and so far after 2 years have had no problems. [EDIT]

Spilling concentrated chlorine onto stone surfaces is most likely going to be a problem, so if your corrosion is limited to the area where you are pouring chlorine (bleach) into your pool, then that is most likely what is going on. If instead the corrosion is mostly where the salty water in your pool is getting splashed out or dripped, say near the steps where you get in and out, then the salinity (salt) of the water is the more likely culprit (though the chlorine in the pool could still be a factor here as well -- you would have to compare your situation with similar stone to others without SWG systems and lower salt-level pools). If the corrosion is generally occurring and not localized, then the corrosion is just natural and this particular stone should probably be sealed on a regular basis (which is probably a good idea to do anyway). In my own pool (without an SWG) our concrete "made-to-look-like-flagstone" hardscape is recommended to be sealed annually and we do so and have seen no signs of corrosion after 3 years (with the exception of one small area of grout far away from the pool that probably just had some imperfection to start with that has pitted a bit).

What your pool builder said is bogus, at least as far as the type of chlorine you are using in your pool. If he meant you spilled concentrated bleach (or had it splash when you added it to your pool), then he has a point, but if he just means the general pool water having chlorine in it that came from SWG generation vs. bleach vs. Cal-Hypo vs. Trichlor vs. Dichlor, then he's absolutely, positively wrong. No matter what the source of chlorine is, once it is in your pool it is the same substance. Having CYA in your pool will lower chlorine's effectiveness and that also means its corrosive capability, but that CYA will affect all sources of chlorine the same (since the chlorine part in water is identical from all sources). If there is a problem unique with having an SWG, then it is most likely the increased salt level more than anything else (at least, in my opinion). If you have a good reseller of stone materials who really knows and understands your particular stone (both coping and hardscape), you could ask them if there is anything you can do to reduce corrosion, such as using a sealer or, in the worst case with a stone that is very susceptible to salt and cannot be easily sealed, that you can't use a salt pool with that stone.

Let us know where this corrosion is occurring -- that will be interesting for us to help figure this out as to what the main factor is (since there are generally multiple factors contributing). You mentioned that it is the coping, but is it the underside of the coping that gets splashed from water all around the perimeter of the pool and is it also on the top surface where you get in and out of the pool?

[EDIT] Finally, do you have a full set of water balance numbers you can post (pH, TA, CYA, CH, TDS or salt, Temperature)? Limestone is mostly calcite which is calcium carbonate. So if your water balance was corrosive in the calcium carbonate saturation sense, then that could be a problem. I have found that the traditional Langelier Saturation Index incorrectly accounts for TDS and temperature (both use a "log" relationship in the formula but that does not reflect the actual relationship) but that the error for a 3000 ppm salt pool is only 0.1 which isn't much at all. My guess is that your water balance is OK, but it's worth checking nevertheless. Also, do you live in an area with acid rain? [END-EDIT]

Richard

Thanks for the replies. it seems to be occuring around the entire perimeter of the pool, both on the bull nose edge and on top. It is not any more noticeable on the areas by the steps as compared to the areas where someone would typically enter/exit. What is interesting, though, is that is does not seem to be occuring much around the spa, which is elevated from the pool, but gets just as much splash activity from the kids getting in there, ect. Same water.
As far as my water balance numbers, my cya is 80, my salt is 3000-3200 ppm, chlorine level is usually 1ppm, and i usually have to supplement my generator with bleach to achieve this level, especially in the summer(aquarite is set on 50-75%). I try to keep my ph at 7.6, but it definitely wants to creep up. I use muratic acid to keep it down, adding about a pint at a time.
As far as acid rain, i don't think so. I live in central texas, and everything here is limestone,(my house, my deck, my fence). In fairness to my builder, at the outset he stated that he knew nothing about salt generators, and i don't think pool chemistry is his thing. Thanks for your interest in this issue and i'll be happy to provide any additional information i can.

That's interesting about the spa. You say it's the same water, but it's elevated in temperature isn't it? That would make it less corrosive and more saturated with calcium carbonate (but then after splash out, I would expect it to cool off and be more corrosive again). What is your Calcium Hardness (CH) level? I saw everything else in your post, but not that (also what is the temperature of your pool and of your spa, typically). Also, if your spa has jets, then I expect that it's pH might be higher than the pool (due to more aeration and therefore more carbon dioxide outgassing) and that also makes the water less corrosive (assuming your pool and spa water aren't thoroughly mixing which I assume they are not since otherwise you couldn't keep elevated spa temperatures for long). Have you ever checked your spa pH separate from your pool pH? Also, have you ever checked your spa's FC separate from your pool FC? Those would be interesting numbers. Though the salt may be a contributing factor, it may be that your pool water chemistry is on the corrosive "edge" to begin with so that salt makes it worse. Perhaps keeping the pool more saturated with calcium carbonate *might* help. Let me know the extra info and we'll see if I'm full of it!

Richard

Richard, yes, it is elevated 18 inches. my calcium hardness level is around 300, my total alkalinity is around 105 (both these nos from pool shop analysis from 18 mos ago). the temp varies greatly with the time of year; right now it is 53 degrees. in the summer, it will be 85-90 deg. i just checked temp in both, and they are both 53. the pool and spa share the same filtration equip, and when the pump is running in its daily routine, the spa is overflowing, mixing spa water with the pool water. The spa has jets, but i just checked the ph in the pool and spa, and they are the same (7.8) as for the FC, i just checked it in both and have none showing up in either spa or pool. This time of year, with the water typically in the 50's, i turn off the generator cell and use a floater with a tablet. water usually stays clear, and i adjust accordingly. i know the generator cell has a definite life span, so i try to conserve its use when i can.

Well, I'm full of it (apparently). Your numbers look good and the pool is properly saturated with calcium carbonate -- I assumed that your pH would drop to 7.6 when the temperature of your water went up to around 88F in the summer. That is typical -- all else equal, the pH rises when the temperature drops and lowers again when the temperature comes back up.

So I'm not sure why your spa coping isn't getting affected as much as the area around the pool. Being elevated shouldn't matter unless it was sloped so that water wouldn't settle on the coping. Apparently, the frequent evaporation of salt water and later rehydration cycling is part of what wears some kinds of stone. So I am at a loss to explain the difference unless the spa pH is different during the summer when it gets used. This summer, try testing the pH between the spa and pool. With the jets running and aeration occurring (which is most likely when the spa is used and the kids are splashing water out), the spa may have increased pH and a small spillover is likely to not be enough to mix with the pool water (though you said it shares the same filtration equipment -- does that mean it truly is the same water and that the spa isn't heated, or does the water go into the skimmer and bottom drains of the pool and come out not only in the pool, but also the spa (with possible additional heating before it gets into the spa?).

Anyway, I'm sorry for the problem you are having. If anyone else has limestone coping, perhaps they can share their experiences, especially if theirs is 3 years old or older. In any event, if your coping is replaced, it should probably be replaced by something that is resistant to corrosion generally, including resistant to salt water (and may require annual sealing, similar to my cement hardscape and coping).

Richard

Something we learned the hard way. We had our pool renovated 5 years ago. We had limestone used instead of tile/coping. We have been having ongoing problems with the limestone flaking, cracking, etc.
One day talking with a stone dealer (for something else, they did not supply stone for pools) I found out there are different "grades" of limestone. The cheaper grades act as the limestone in our pool (which I have been using tri-chlor pucks, bleach only so far).
Anyway, I am no expert but just thought I would pass that on.

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Originally Posted by fofa

Something we learned the hard way. We had our pool renovated 5 years ago. We had limestone used instead of tile/coping. We have been having ongoing problems with the limestone flaking, cracking, etc.
One day talking with a stone dealer (for something else, they did not supply stone for pools) I found out there are different "grades" of limestone. The cheaper grades act as the limestone in our pool (which I have been using tri-chlor pucks, bleach only so far).
Anyway, I am no expert but just thought I would pass that on.

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So this would indicate that the quality of limestone is a primary factor since your pool is not a salt pool (no SWG). Technically, even non-SWG pools have salt in them, of course, but generally it starts at around 350 ppm (the sodium from the bicarbonate and the chloride from the calcium chloride, plus some more chloride from muriatic acid) but usually stays below 1000 ppm with regular dilution from backwashing.

Just to be sure, do you have a DE or sand filter that you regularly backwash or do you have a cartridge filter and yet manually drain and fill part of your pool water? I'm just trying to get a handle on the salt levels in your pool.

Richard

My un-educated theory? Limestone varies in hardness based on the quarry, hardness of the particular seam being mined, ect. Leuters limestone (which is what my coping is) is from a quarry in Leuters Texas that is known for limestone that is particularly hard. However, limestone is a natural product and therefore somewhat un-predictable. The coping stones around my spa are larger stones than the rest of the pool. My guess is that the larger (spa) stones were mined from a different seam than the rest of the pool. The pool stones were probably mined from a seam that had a stretch of soft stone in it. I probably got that batch of stone that is too soft to be used as coping. For that matter, who knows if the stuff really came from Leuters. The name has become analagous with hard stone and a stone vendor can call any stone Leuters and who would know the difference? Just my therory, but i know that a lot of limestone, for instance the flagstone on my deck, is soft and flakes, and would not be suitable for use as pool coping. So, I am going to have it replaced and will apply the best sealer i can find, but based on what i have learned here, the salt water generator is irelevant as to whether it will detoriorate or not.

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Originally Posted by chem geek

Just to be sure, do you have a DE or sand filter that you regularly backwash or do you have a cartridge filter and yet manually drain and fill part of your pool water? I'm just trying to get a handle on the salt levels in your pool.

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I have a DE filter and backwash as needed (via pressure readings).

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Originally Posted by fofa

I have a DE filter and backwash as needed (via pressure readings).

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Thanks. So your salt levels in your pool are probably in check and well below 1000 ppm. That would make the quality of the stone the dominant factor in your corrosion. So "craiga's" pool builder shouldn't be using the fact that a pool has salt or an SWG as an excuse for what may be poor quality stone.

Of course, the problem is that there may be times when higher salinity is indeed a problem especially with certain types of stone and yet this whole issue gets muddled as fingers point to whom to blame. And there are other times when not using CYA, with the result being very high disinfecting/oxidizing chlorine levels, may be the primary source of corrosion (a possibility in this thread).

Richard

And yet, salt gets the blame.
I think since it's the newest (not really) guy on the block, it gets the brunt of the blame. The problem is that for many years, limestone and decks have gone through the same damage problems, but what did they blame back then?
Bad batch of cement, calcium, aggregate, sand, water quality, etc. Believe me, after 20 years in the pool industry, I've heard all these. So now that salt systems are becoming more popular, let's blame them!

What's important to note is that these same issues occur on pools without salt systems.

Salt damage? How long do seawalls last before the sea water, which by the way is on average, 10 time greater than a salt water pool, starts to show damage it? Hmm, me thinks a good number of years! I can't recall when the City of Ft Lauderdale had to rebuild the "Wave Wall" along the beach boardwalk. I grew up in South Florida, 15 minutes from the beach, and the same seawall that I fished off of 35 years ago, is the same one that I fish on today. Awesome snook fishing by the Haulover Beach area!
So how does a pool deck delaminating after a few years mean that the salt system is the cause?

Richard, by the way, it is typically a bleach pool that shows a higher level of salinity when maintained this way for 3 or more years without any significant water exchanges. Tab and cal hypo pools are usually minimal in salinity, less than 500 ppm.

I may be defensive on this issue because there are so many "old school" pool service guys and builders that refuse to come into the 21 century. Salt systems for them is just something new to learn about and takes them away from what they've known and done for years. Not knowing about salt systems mean loosing accounts, so it's in their best interest in speak badly about salt systems.
In the 20 years of dealing with salt systems, guess how many deck damage issues I've had to deal with in South Florida? ZERO.
While I've heard of such conditions, I have not seen such conditions that were directly accountable to a salt system.
Staining from salt, sure I would admit to that occuring with certain salts.
Corrosion from salt, sure I would admit to high chlorine or over salting a pool causing a certain level of corrosion damage.
Electrolysis? yeah, if the pool isn't bonded properly, installed correctly, or there's an electrical grid issue, there may be stray voltage introduced into the pool due to a salt system.

Sorry for being long in my response. I think I'll take this up in the China Shop.