Wet Room Floor Leaking

What's happening?

A wet room has no tray, so the waterproofing is the floor itself. Everything depends on a continuous tanking membrane bonded to the substrate, taken up the walls beyond the wet zone, sealed into the drain flange, and only then tiled. Tiles and grout are the wearing surface, not the waterproof layer — water passes through grout as a matter of course, and the membrane underneath is what catches it. When a wet room leaks, the tanking is either missing, stopped short, punctured, or not sealed into the drain, and the water goes straight into the floor structure. Because there is no tray to contain anything and the whole floor is in use, a failed wet room does more damage faster than any other bathroom leak, and it cannot be patched from above.

What usually causes it?

• No tanking membrane at all, with tiles laid straight onto board and relied on to keep water out
• Tanking stopped at the tile line instead of being carried up the walls past the wet zone
• The membrane not sealed into the drain flange, so water runs behind the drain rather than into it
• A puncture in the membrane from a later fixing — a screen fixed through the floor, a rail, a screw
• The floor formed with no fall, or a fall running the wrong way, so water stands and finds the weakest joint
• Plasterboard or standard timber decking used where a tile backer board and a rigid, deflection-free substrate were required
• A deflecting timber floor cracking the tiles and the membrane bonded to them

When should you call a bathroom fitter?

Call a bathroom fitter as soon as you suspect it, and stop using the shower in the meantime. A failed wet room is a strip-out and rebuild of the floor construction — substrate, falls, drain, membrane and tiling — not a repair. If the room was built recently, get it looked at urgently either way: the longer it runs, the more of the floor structure has to come out with it.

What will the bathroom fitter actually do?

• Water-test the floor and the drain separately to prove whether the failure is at the drain or across the membrane
• Strip the tiling and the substrate back and inspect the joists and decking for rot
• Rebuild the deck to a rigid, deflection-free substrate with the correct fall formed to the drain
• Install a continuous tanking system, taken up the walls beyond the wet zone and bonded into the drain flange
• Flood-test the waterproofing before a single tile is laid
• Tile, grout, and form all changes of plane in flexible sealant, then test the finished shower in use

What a wet room floor is actually made of

1. A rigid substrate with deflection controlled — not ordinary chipboard decking.
2. A former or a screed shaping the fall to the drain across the whole wet zone.
3. A drain body set so its flange finishes level with the substrate.
4. A continuous tanking membrane bonded down, up the walls past the wet zone, and into the drain flange.
5. A flood test of the membrane before tiling starts.
6. Tiles, then grout, then flexible sealant at every change of plane.