Tanking (wet room)
Plain English. Practical detail. UK context.
Wet room tanking is a waterproofing system beneath the tiled finish that protects the building from shower water. It can use compatible liquid-applied membranes, sheets or proprietary waterproof board systems. Tiles, water-resistant grout and adhesive do not by themselves replace a properly designed and detailed waterproofing layer.
Last reviewed: (editorial review against the public sources listed below).
Design the water route first
The shower flow, drain capacity, floor falls and doorway detail must be coordinated. A membrane cannot make water run uphill or compensate for an undersized outlet. The substrate must support the chosen finish without unacceptable movement. Timber floors, screeds and board walls need different preparation and load assessments. Ask for a plan showing the waterproofed area and a section through the drain and threshold. Accessible use can affect falls, transitions, slip risk and the space available for assistance.
The details that make the system
Corners, pipe penetrations, niches, board joints and the drain connection are common weak points. A complete system specifies the necessary tapes, collars, adhesives and primers as well as the main membrane. Mixing components from different systems without approval can lose the intended compatibility. The installer must achieve the prescribed coverage or thickness and allow the required curing. Photograph the completed waterproofing before tiling, with useful close-ups of the difficult junctions, so it is not merely an invisible claim at handover.
Common mistakes
Green moisture-resistant plasterboard is not automatically a waterproof system. A thin coat of liquid membrane with missed corners is not adequate because the tin says tanking. Silicone around the finished shower does not repair a discontinuous hidden membrane. Fixing screens or accessories later can puncture the protection unless the penetration detail is planned. Do not assume a basement tanking product is appropriate for a tiled shower, or that a shower membrane can resist external groundwater pressure.
Guidance, alternatives and handover
The Tile Association explains the relationship between wet-area backgrounds, complete assessed systems and BS 5385 guidance. BS EN 12004 concerns tile adhesives; BS EN 13888 concerns grout. A conventional shower tray with correctly designed upstands and connections is an alternative layout, but still needs suitable surrounding waterproofing details. Agree testing where appropriate to the system and project. Record products, curing information and restrictions on drilling, and supply maintenance advice for joints, seals and drainage.
Frequently asked questions
Is waterproof grout enough?
No. The waterproofing layer and its connections protect the structure behind the tile finish.
Can I mix any membrane and tape?
Only where the relevant manufacturers approve the combined system.
Can the room be used immediately after grouting?
Follow the complete system’s curing and return-to-service instructions; the surface looking dry is not sufficient.
Is waterproof grout enough for a wet room?
No. Grout and tiles are finishes, and joints and penetrations still need a suitable waterproofing design. The underlying tanking system provides protection to vulnerable construction.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.