How this calculator works
The tanked area is the shower floor plus the walls, less openings. The walls are the run of wall times the height, and the run depends on how many walls are tanked: an alcove shower has the back wall and two side walls. The tanking itself is the area times the coverage per square metre for the two coats, plus an allowance for waste. Tape covers the floor-to-wall joint and the vertical corners.
Worked example: a 1.2 × 0.9 m alcove shower tanked 2 m high has 7.08 m² to cover: 1.08 m² of floor and 6.00 m² of wall. At 1 kg per m² with 10% extra that is 7.8 kg, which is 2 tubs of 7.5 kg, and 8 m of tape. A 1.5 × 0.9 m shower is 7.95 m² and 8.7 kg. A 2 × 1.5 m wet room with four tanked walls is 17.0 m² and 18.7 kg.
Assumptions and sources
- Assumptions used: 10% waste added; 1.0 kg per m² for two coats; tape over the floor-to-wall joint and every inside corner.
- This counts the tanking on a flat floor and the walls. A tray former, a bench, a niche, the drain and the pipe penetrations all need extra tanking and the fittings from the same system. Tanking sits behind the tile and the tile adhesive: it is not a finish. A tanking kit or system states its own coverage, the number of coats and the drying time, and those rule. Follow the instructions of the product and of the building regulations for wet rooms.
The formula and a worked example are shown above, so you can check any result by hand. Read how we calculate and check our numbers. Results are estimates for planning: supplier products vary, so check the size printed on the label.
Tanking for common showers
Alcove with three walls, tanked 2 m high, 10% waste, 1 kg per m², 7.5 kg tubs.
| Shower | Area | Tanking | Tubs | Tape |
|---|---|---|---|---|
| 0.8 × 0.8 m | 5.4 m² | 6.0 kg | 1 | 8 m |
| 0.9 × 0.9 m | 6.2 m² | 6.8 kg | 1 | 8 m |
| 1.2 × 0.8 m | 6.6 m² | 7.2 kg | 1 | 8 m |
| 1.2 × 0.9 m | 7.1 m² | 7.8 kg | 2 | 8 m |
| 1.5 × 0.9 m | 7.9 m² | 8.7 kg | 2 | 9 m |
Tips before you buy
- Tank the whole of the wet area, not just the floor. Water splashed on the walls gets through the grout, so the tanking behind the tile is what keeps the wall dry.
- Prime the board first if the maker asks for it, and apply the coats with a roller or brush to an even thickness. A thin patch is a leak.
- Press the tape into the first coat at every corner, the floor-to-wall joint and around the drain, then cover it with the second coat.
- Let the tanking dry for the time stated before you tile: it is shorter for the fast-drying products and longer in cold or damp rooms.
- Use the adhesive that the tanking maker names, and flood-test a tanked floor before you tile if the system allows.
Tools & materials for this project
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Frequently asked questions
How much tanking do I need for a shower?
Add the floor and the walls to be tanked, then multiply by the coverage of the product. A 1.2 × 0.9 m alcove shower tanked 2 m high is 7.1 m², which takes 7.8 kg for two coats at 1 kg per m², or 2 tubs of 7.5 kg.
How many coats of tanking do I need?
Two coats is usual for liquid tanking. Mapei AquaDefense is two coats of about 0.4 mm for 0.8 mm in all. Check the instructions of the product you buy.
How high should I tank a shower?
Cover the whole of the wet area: in a shower that is the full height of the walls the spray reaches, often up to the ceiling. The product instructions say what the maker requires.
Do I tank the floor as well as the walls?
Yes. The floor of a shower or wet room is the first part that gets wet, and the joint between the floor and the wall is where it usually leaks. Use tape in the corners.
How long does tanking take to dry?
It depends on the product: fast-drying ones can be tiled in a few hours and others need a day or more. Follow the label.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.