Preparation
Tanking membrane, tape and corner pieces
- where
- membrane needed (kg)
- area to tank (m²)
- membrane consumption, all coats (kg/m²)
- packs to buy
- pack size (kg)
- reinforcing tape length (m)
- wall-to-floor junction length (m)
- internal vertical corners
- tanked height (m)
- board joints and other junctions (m)
Explain this equation
Works out the liquid tanking membrane for a shower or wet room, the reinforcing tape for the corners and junctions, and the number of internal corner pieces.
A is the area to tank and Cm the membrane used per square metre over all coats, so M is the membrane weight and B the packs of size Ps. Lt is the tape length: the wall-to-floor junction Lj, plus each internal vertical corner nc running up the tanked height H, plus any board joints Lb.
Membrane use scales with area at the coverage the manufacturer states for the full system thickness. Tape goes wherever two planes meet or boards join, because those are the lines that move and crack; so it is a simple sum of those lengths.
Sense check: an 8 m² shower area at 1.2 kg/m² needs about 9.6 kg of membrane. A corner shower with a 3.6 m junction and two corners tanked to 2 m needs about 7.6 m of tape.
Watch out: tape lengths do not include overlaps at joins. Pipe seals and drain collars are extra.
Liquid tanking membrane for a shower or wet room, the reinforcing tape for the junctions and the number of internal corner pieces.
Enter your values to see the result.
Good to know
Mapei state a minimum of about 1.2 kg/m² for Mapegum WPS in two coats, never under 0.8 mm wet, with Mapeband tape bedded into the first coat at wall-to-floor and wall-to-wall joints and pre-formed corner pieces and pipe seals. Add tape for board joints if the system requires it. Allow for tape overlaps at joins. Kits are sold by the area they cover, so compare the kit area with A.
Common mistake
Tanking only the shower tray area. BS 5385-4 and manufacturers expect the whole wet zone to be tanked, with the floor and lower walls in a wet room.
Limits
Membrane only; primer is separate. Consumption depends on the product and coat thickness; use your system data sheet. Tape length excludes overlaps (typically about 50 mm) and pipe seals.
Sources
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the tile, adhesive and grout manufacturers’ instructions, BS 5385 and the Tile Association guidance. Coverage rates vary by product and substrate. Check prices and VAT rules with your own records and HMRC.