Wet-Room Tanking Before Tiling

Tiles and grout are a wear layer, not a waterproofing layer. Water passes through grout lines and around the edges of tiles, and once it is behind the finish it sits against the screed and the structure below. Tanking is the waterproof layer that goes on before tiling, so the wet area stays protected even when the finish does not.

The most common failure is sequence. The tanking has to go onto a sound, prepared substrate before the screed and tiles, and it has to be continuous across the floor and up the walls in the wet zone. Retrofitting it after tiling means removing the finish — which is why it is worth getting right the first time.

Detailing decides the outcome. Wall-to-floor junctions, internal and external corners, pipe penetrations, the shower outlet and drain, niches and the door threshold all interrupt the membrane. Each one is reinforced with a compatible fabric or tape and sealed into the system, not left as a butt joint.

We use liquid-applied membranes for most wet rooms because they form a seamless layer around complex geometry, and sheet or cementitious systems where the substrate or the programme calls for them. The choice follows the substrate, the finish and the movement expected — not what is quickest to install.

Before tiling we flood-test the area and record the result. A wet room that passes a flood test before the tiles go down is a wet room that will not be opened up again in a year.