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Guide

Tanking a shower or wet room before it is tiled

Tanking a shower or wet room costs £100 to £250 depending on the area, in MyJobQuote's 2026 floor tiling guide, before the tiling. It is the waterproof layer behind the tiles, needed because tiles and grout let water through. BS 5385-4 covers tiling in wet conditions.

Updated

Illustration: a shower corner before tiling, its walls and floor covered in green tanking membrane, with corner tape, sealed pipe collars, a floor drain and a tub of liquid membrane

Why does a shower need tanking?

Glazed tiles shed water, but grout is porous and fine cracks open in it over time, and silicone joints age. Water that gets behind the tiles soaks the wall or floor, softens plaster and timber, and shows up months later as a stain on the ceiling below. Tanking puts a continuous waterproof layer behind the tiles so that the tiles become the finish, not the waterproofing.

What are the types of tanking?

Liquid membranes are painted or rolled on in two or more layers, with reinforcing tape at corners. Sheet membranes are bonded to the wall and floor with overlapped and sealed joints. Waterproof backer boards replace the wall surface, and every board joint and screw head is sealed. All three work when used as their maker says. What fails is a mix of products, or gaps at the weak points: internal corners, where wall meets floor, pipe entries and the drain.

Illustration: a wet room floor falling to a linear drain, with the green tanking membrane and tape still showing where the tiling stops
A wet room floor falling to a linear drain, with the tanking membrane and corner tape still showing beyond the tiles.

How is a wet room tanked?

In a wet room the whole floor drains, so it is formed to a fall towards the drain, often with a pre-formed sloping board, and the walls and floor are tanked as one. The drain must be a type that clamps the membrane, so water on top of the membrane still reaches it. Many systems ask for a curing time, and some tilers flood test the floor before tiling.

What does tanking cost?

MyJobQuote's floor tiling guide (July 2026) gives £100 to £250 for waterproofing, depending on the area. Tiling on top is extra: £20 to £40 per m² labour in MyJobQuote's bathroom guide, or about £50 per m² as Checkatrade's average. Stripping out a leaking shower first adds to both.

What record should you keep?

Ask the tiler for photographs of the tanking before it is covered, especially the corners, pipes and drain, and a note of the product, its batch and the date. If a leak appears later, that record shows what was done and helps find the cause.

Tanking in section: substrate, primer, tanking membrane with tape across the corner, tile adhesive, tile and groutTileTile adhesivesolid bed, no voidsTanking membranewalls and floor in onePrimerwhere the system asks for itSubstratebacker board or screedTape across the corner,and at joints and pipesGrout in the joints,flexible sealant in the cornerSection through a shower corner. The membrane is continuous; the tile and grout are not the waterproofing.

Common questions

Do you need to tank behind a bath?

If there is a shower over the bath, yes, the walls it wets. Behind a bath with no shower, many tilers still tank the first row or two above the bath edge.

Can tanking be done after tiling?

No. It goes behind the tiles. A shower that leaks through failed tanking has to be stripped back to the wall and done again.

How much does tanking a shower cost?

MyJobQuote's 2026 floor tiling guide gives £100 to £250 for waterproofing, depending on the area, plus the tiling.

Is a tanking kit enough for a wet room?

A kit from one maker, used as its instructions say, with a compatible drain and a properly formed fall, is what most tilers use. Mixing products from different systems is where problems start.

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