How is stone doing with a salt pool?

womanownedSeptember 30, 2010

I am curious to hear your experiences as consumers whether you have had issues with stone erosion or discoloration with a salt pool. Good and bad. Did you have the stone sealed? Have you resealed it since the initial application?

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We have a four year old pool with salt. Flagstone coping that is sydney peak. Waterfall is different stone, can't remember. No problems. We never sealed anything. Have been very happy.

    Bookmark   October 1, 2010 at 11:00AM
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We have exactly the same concern as we really want a salt water pool but have heard and read different opinions on the effects salt water will have on a nice stone deck (e.g. travertine). Any other experiences out there? (preferably a few years old) Are other stones recommended?

    Bookmark   October 1, 2010 at 5:42PM
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We have a 4 years old salt water pool with quartzite coping, flagstone lower deck and travertine upper deck. No sealing of any kind has ever been done. There have been absolutely no problems with any of the stone.

    Bookmark   October 2, 2010 at 7:50AM
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Those replying may want to include the location as well as what type of flagstone you installed. Flagstone is a very general term. Some can be hard and durable while others can be in porous and others flaky. The different colors of flagstone come from the different minerals within the rock. For example some flagstones have a higher amount of sand while others have more clay.

Typically northern/eastern states have harder flagstones than southern. But just because you live in the south doesn't mean that your builder/contractor didn't use a northern type of flagstone. Even in the southern states, Oklahoma flagstone, Arizona flagstone, and Tennessee flagstone can all be quite different in the types of minerals present.

In flagstones with a high percentage of clay (can be any color) the flagstone is more susceptible to salt water erosion/damage. The scientific reason is because the clay particles are very small. The water (with dissolved salt) flows inbetween the clay particles....remember were talking microscopic here. There won't be "leakage" just very slight getting wet at the surface (you might notice a change in color when the stone gets wet.). Over time of hot and cold changes - it not just time - it really just temperature changes, the clay particles will swell and contract. In addition, the water will evaporate leaving the salt behind. When the salt was in the water, it was dissolved into Na and Cl. Each individual Na and Cl are very small. But when the water leaves/evaporates, then the Na and Cl will recombine to make salt again - which is a larger molecule. The size of this molecule cannot fit between the clay particles. Both the temperature change of the clay as well as the salt molecule can cause pressure on the rock and can allow it to break/crack/erode/pit, etc. (This is the reason places with high clay in their soil - like Houston - have ground water pipes burst - because of the natural swelling/contraction during temperature/water changes in the soil. The same thing - albeit on a smaller scale - is what is happening to those that may experience damage.)

    Bookmark   October 2, 2010 at 10:57AM
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The sodium and chloride ions that are formed are larger than a salt molecule.

The chlorine will gas off if there is evaporation. Might leave a little sodium, but I doubt it.


    Bookmark   October 2, 2010 at 3:15PM
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I should add that weathering, be it from freeze/thaw, temperature changes, etc... on stone has a far greater effect than absorption/evaporation deposits.

The use of soft stones by a consumer as coping is usually discouraged because it won't last. As an extreme example, while very porous, talc, the softest measure on the hardness scape, isn't soluble in water but will erode rather quickly due to being bumped and scraped.

I sincerely doubt, unless some chemical reaction with what impurities are in the water happen, that any deposits like sodium, reformed salt, etc..., would create a meaningful stress on the coping, contributing to it's break down.

Poured in place concrete is slightly porous and so are most brick pavers, yet they will last and last. Some other materials, such as certain sedimentary and igneous rocks, fracture easily in the cold due to ice expansion. Typically, the harder and denser stones last longer. Tile is similar.

I have never knowingly seen damaged coping or stone work attributable to any deposits left from evaporation in salted pools. It's effect isn't that significant.

I have seen corrosion of metals, such as stainless, as a result of stray currents. I have used zincs to reduce, close to elimination, these reactions.

I have seen stone with a significant iron content cause rust stains and iron presence in water where the fill had none. I don't think salt has a lot to do with that. Iron is a metal, as is sodium and as such, is soluble in water.

What might be more useful is a chart of known durables.


    Bookmark   October 3, 2010 at 8:23AM
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I've built at least 1000 pools with salt water chlorine generation.
Here's been my experiences;
Kiln fire swimming pool coping bricks do fine and so do their pavers that match.
Harder/denser stones such as Oklahome Wister, Tennessee Crab orchard, Pennsylvania Lilac, Quartzite, etc... do OK.
Softer rocks like Arizona Rosa, Buff, Peach, Sedona Red etc... don't do well at all, this also goes for Mexican Travertine coping bricks such as Noche, Durango, etc....
Turkish Travertine does better than Mexican Travertine.
I suggest sealing soft rocks and travertine.
Slate coping bricks fall right in the middle, they're a coin toss.
Don't use any unsealed flagstone for waterline tile, they'll show poorly within a year or two.
When placed as patio decking dark flagstone, home bricks, and concrete patio pavers show chalkiness from evaporated salt due to splash out.

SWG's have been the rage for the past 10 to 12 years but are now seeming to fall out of favor with the buyers.
For the past decade 95%+ of my new starts have been salt. This year it's down to about 70%.

See ya,

    Bookmark   October 3, 2010 at 3:47PM
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It sounds like a sealed travertine could work but quartzite would be better. I assume quartzite does not need any treatment/sealing?
If we go with a travertine (Turkish I guess), does anybody know how often it needs to be sealed? Also, does it need to brushed in order for it not be slippery? It seems that honed and unfilled may also work but probably a bit more slippery than brushed?

    Bookmark   October 3, 2010 at 7:16PM
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NO manufactured stone!

    Bookmark   October 3, 2010 at 8:22PM
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Quartzite is so hard and dense you probably couldn't seal it if you wanted to! It is also more expensive to buy and to work than softer stones but it is a great material. It would always be my first choice as long as I could afford it.
Our Turkish travertine upper deck is unsealed and holds up well here in Florida, but I filled the larger holes as they collected dirt and didn't look too good. It is sometimes a little slippery (mostly to toddlers) when very wet.

    Bookmark   October 5, 2010 at 5:51PM
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additional question to all the pool builders in regards to salt and flagstone. i have oklahoma flagstone for my coping and it was sealed when we started up. first, how often does that need to be sealed and second, does the flagstone spa spillover need to be sealed as well????

thanks for the input!

    Bookmark   October 6, 2010 at 10:49AM
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I have bitteroot flagstone, we have a solid ring around (1 inch widee) the hot tub (that overflows into pool) and we get rings at different water levels when the rain comes bc we didn't put anutomatic drain in (since it was against code) but I wish we had. I still love the flagstone look but I definitely think I was misled on which flagstone will work well with a salt pool.

    Bookmark   October 6, 2010 at 5:00PM
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