A swimming pool is an unusual waterproofing case because the 'positive' side — the side under water pressure — is the interior, the opposite of a typical basement wall. That inverts the usual logic: the coating or membrane that matters most is generally applied to the inside face of the pool shell, in direct contact with the water it's holding back.

Cementitious coatings are common on pool shells for the same reasons they suit water tanks — strong bonding to concrete and the ability to handle constant water contact. Where the shell is prone to hairline cracking from ground movement or structural settlement, a polymer-modified or crystalline system adds crack-bridging or self-healing capacity that a purely rigid coating lacks. For an empty or partially drained pool with active leaks at specific cracks, polyurethane injection is a targeted repair option, sealing the leak without needing to strip and recoat the whole shell.

Where the pool sits below the surrounding water table — common on sites with a high seasonal groundwater level — the shell also needs to resist water pushing in from outside when the pool is drained for maintenance, which is where genuine below-grade waterproofing principles apply on the exterior face as well. A pool designed without accounting for this can, in the worst case, be pushed upward out of the ground by groundwater pressure when emptied, which is why drainage and hydrostatic relief design matter as much as the coating specification itself on sites with poor natural drainage.