QUESTION

I have a personal question for you. We are re-doing our backyard, and the pool coping we picked out is a Indian black limestone coping, see the attached photo. We were told by the installer we should not seal it, even with a penetrating sealer because it causes other issues like visible scratching, flaking, etc.

Can you give me your opinion on if we should seal it, and if you think it should be sealed, what product should we be using?

ANSWER

Always take what the contractor says with a grain of salt and make sure there is documents backing it up.  Don’t assume they are doing things correctly and read the directions that they likely don’t to make sure they are using the products correctly.  You have to be the QC Guy.

Limestone falls under ASTM C568.  There are 3 classifications: Low Density, Medium Density and High Density Limestone with different physical properties.  Normally you only want to use medium or high density limestones on the exterior in warmer CA areas.

Whether the limestone performs well or not depends on the application and how it is installed. It is when the stone is subjected to excessive moisture that it ends up spalling. You have to consider drainage and moisture control in the installation design.  Best is to bond over concrete over a liquid applied waterproof membrane.  So the installer should be installing the coping over a concrete pool bond beam.  That should be waterproofed with a liquid applied product like Laticrete Hydro Ban or Custom RedGard and then the tile bonded to the membrane with an ANSI A118.4 or .15 thinset mortar.  They should achieve full thinset contact between the membrane and the back of the stone. No voids.  The front joint below the coping in the pool should be caulked with a sealant like Custom 100% Silicone that is suitable for swimming pool.  The coping joint on the top back should be filled with an ASTM C920 traffic grade sealant like Sika Flex + Self Leveling Sealant that you can buy at Home Depot in different colors. This bonds tenaciously and makes the joint water tight, and lasts a long time if installed correctly.

The sealers will not cause a problem if they are selected and used correctly.  Sealers are temporary and wear.  They do not waterproof the tile.  There are different types of sealers.  Surface sealers can peal. Penetrating sealers if applied correctly will not peal.  You do have to reapply every year more or less depending on the look or performance that you want to maintain.  Some sealers are enhancers to give a wet look.  Only use the penetrating type.  Miracle 511 Seal and Enhancer sealer or Dry Treat Color Enhancing Sealers.  Or they both have penetrating sealers where sealing it doesn’t change the appearance of the stone that much.

Good luck!