SALTWATER POOLS AND STONE - A LOVE AFFAIR THAT CAN GO CRUSTY!
Wars and broken romances have one thing in common – collateral damage! The love affair between saltwater pool owners and natural stone may suffer the same fate if a bit of common sense isn’t applied.
Salt can do nasty stuff to stone! The gnarled and heavily etched rock surfaces on the headlands of any Sydney surfing beach is testament to the power of salt, wind and wave action. Look very closely and you will discover an unassailable truth – some sandstone is amazingly resilient to nature’s wildest forces while other types succumb horribly.
Stone survival on any coastline is very Darwinian – the strong survive and the weak disappear. The performance of stone paving material varies in the same way. Poor quality material doesn’t last. This is especially so around saltwater pools. Traditionally chlorinated pools pose little risk to natural stone.
Salt can cause devastating damage to just about any building material whether it is metal, concrete or stone. Some stone is quite resistant to salt attack – a property that can be determined quite easily by laboratory testing. Some stone suppliers invest heavily in testing their stone to ensure that the product used is fit for the intended purpose. Businesses that provide this information deserve praise and are worthy of support, because too much poor quality stone is being sold by too many shoddy operators.
Salt water pools and sea spray in coastal areas can threaten some stone surfaces. Damage ranges from pitting and flaking through to delamination. Sealing will reduce the movement of salt laden moisture into the stone sub surface where most of the damage occurs. Regularly hosing down wet areas around a pool is the best prevention of all. Increasingly though, concerns about saving water or forgetfulness expose the stone to risk.
Sometimes salt damage occurs because of poor sub-surface drainage around the pool. Many soils are quite saline especially in the subsoil. After rain, soluble salts may rise to the surface permeating the stone from the under-surface. As the stone dries the salt forms crystals that expand in the tiny pores of the stone causing physical damage to the structure of the stone. In these cases salt damage to the stone is usually incorrectly attributed to the pool.
It is vital that stone is laid on properly drained surfaces (substrates) preferably with a waterproof membrane. This will eliminate the threat from below.
Sometimes damage to the stone has been caused by applying an inappropriate sealant. This comes as the biggest shock of all to homeowners because they think they have done the right thing by sealing. It is arguably better not to seal stone exposed to salt than to apply a surface sealer.
Surface sealers can trap soluble salts under the bonded surface layer. Once dry, the crystallised salt can exert such force to the upper layer of stone that it delaminates and flakes off.
If stone tiles are used around salt water pools, only penetrating sealers should be considered as they allow moisture if any exists, to escape from below the sealant film in the form of vapour. This doesn’t happen with surface sealants.
Stone that is laid around the edges of the pool and for two or three layers back from the pool edge should be sealed on all six sides to prevent salt penetration. Adhesives should be used uniformly with no air pockets and grout joints should achieve a 100% coverage so that moisture carrying soluble salt has no chance of penetrating the stone.