How Much Wet Room Tanking Do I Need?

How We Calculated This

Wet room tanking creates a waterproof membrane under tiles to prevent water damage to the building structure:

• Typical wet room: 2m × 1.5m floor + walls to 2.4m height
• Floor area: 2 × 1.5 = 3m²
• Wall area: (2 + 1.5) × 2 × 2.4 = 16.8m²
• Total area: ~20m²
• Membrane per coat: 20 × 1.2 kg/m² = 24kg
• Two coats: 24 × 2 = ~48kg (roughly 2–3 tubs of 20kg)

Tanking System Components

• Liquid membrane: Applied by brush or roller, 2–3 coats, £40–70 per 20kg tub
• Tanking tape: Self-adhesive or bedded in membrane, used at all internal corners and joints
• Pipe collars: Pre-formed seals around pipe penetrations
• Drain collar: Waterproof seal between drain and membrane
• Primer: Some systems require a primer on absorbent substrates

Popular UK Tanking Products

• BAL Tank-It: ~1.5 kg/m² per coat, 2 coats, covers 6–7m² per 10kg
• Mapei Mapegum WPS: ~1.0 kg/m² per coat, 2 coats, covers 5m² per 5kg
• Weber Tec Superflex D2: ~1.2 kg/m² per coat, 2 coats
• Ardex 8+9: Two-component system, ~1.2 kg/m² per coat

Building Regulations

Wet rooms in the UK must comply with BS 5385 (tiling) and BS EN 14411 (ceramic tiles). The tanking membrane must be continuous and waterproof across floors, walls, and all joints. A properly installed wet room typically requires Building Control sign-off, especially if it involves structural alterations to the floor for the drain fall.

Tips

Allow each coat to dry fully (typically 2–4 hours) before applying the next. Apply coats in alternating directions (horizontal then vertical) for full coverage. Always use the tape at internal corners, floor-wall junctions, and around penetrations. Test the waterproofing with a flood test (24–48 hours) before tiling.