Mastic (also called Deck-O-Seal) – What Is It and Why Is It Important?

What is mastic?

Mastic is an expansion joint sealant that is used to seal expansion joints around swimming pools which are subject to movement. The product provides a firm, flexible, water proof seal over the expansion joint that typically surrounds the swimming pool—and is typically between the pool coping and the concrete deck. It is resistant to swimming pool chemicals.

Why is it necessary to seal the expansion joint that surrounds my swimming pool?

The reason that it is necessary to seal the expansion joint that surrounds the swimming pool is to keep the water out.   Allowing water to enter the expansion joint area can cause soil movement (which causes pool or deck movement) and also the possibility of freeze damage to the tile, coping, and gunite beam.

Why would it need to be replaced?

Typically every few years mastic becomes dry and sometimes separates from the coping or the concrete deck due to movement. This separation allows water to penetrate, which could cause further movement or freeze damage to the tile, coping, and gunite beam.

Do you need to hire someone to do this or can you do it yourself?

Most of our clients hire us to do this, but some prefer to do it themselves. We can give you an estimate of what it would cost on your pool, or we would be glad to coach you thru it if you prefer to take care of it yourself.

(Please be aware that it is a fairly labor-intensive and time-consuming project—at least several hours in most cases.)