Wet rooms: membrane and tiles

The substrate must be firm, stable, dust-free and even. Hollows may be at most 1 mm deep over a 250 mm span (SBi 252). An unstable or uneven substrate must be remedied before the membrane is applied — the membrane does not correct faults.

The fall must be in place in the subfloor before tiling — guideline minimum 1 % (10 mm/m) in general and minimum 2 % (20 mm/m) under the shower area/bath (BR18 requires sufficient fall, but no percentage). A fall created on top of the tiles cannot save a flat subfloor.

Use a complete MK-approved (ETA-Danmark) or ETA/TGA-documented wet-room system where primer, membrane, adhesive and grout come from the same approval. Do not mix components from different approvals — the documentation is then void.

Prime the substrate with the system's primer as instructed in the MK approval. The primer binds dust and controls absorption so that the membrane bonds and cures correctly.

Apply the liquid-applied membrane in at least 2 coats to a total finished thickness of typically at least 1 mm — the supplier's MK approval governs the exact requirement. Let each coat dry for the specified time so that the layer is uniform and watertight.

Reinforce all corners and transitions (floor/wall) with the system's sealing tape, embedded in the first membrane coat, and fit collars at all pipe penetrations. There must be no pipe penetrations in the water-exposed floor zone (BR18 § 339).

The membrane must cover the entire water-exposed zone: in that part of the room, walls and wall linings, including joints and pipe penetrations, must be watertight (BR18 § 339). How far the zone extends beyond the shower recess, and whether foil with a clamping ring is needed at the drain, is stated in SBi Guidelines 252 and the specific MK approval — always check its scope.

Use tile adhesive of at least class C2 (adhesion ≥ 1.0 N/mm²) in accordance with DS/EN 12004-1:2017 — this is the minimum requirement in wet rooms under SBi 252 practice. Choose C2 S1/S2 for underfloor heating, large tiles and structures with movement.

Place elastic movement joints in all corners and transitions: width min. 6 mm, filled with silicone in accordance with DS/ISO 11600. The ordinary tile joints are filled with cement-based tile grout from the system once the adhesive has cured.

Measure the floor fall to the drain (guideline min. 1 % in general, min. 2 % in the shower area) with spirit level and folding rule, and inspect visually: no cracked tiles, uniform joints and closed, elastic movement joints. Fill in the final inspection form (x.500).