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Waterproofing membrane calculator
Work out liquid membrane for wet areas, balconies and flat roofs, including the wall upturns and reinforcing tape that most quick estimates forget.
How the calculation works
A liquid membrane covers more than the floor. The upturn up each wall adds area, and every corner, drain and pipe needs reinforcement.
Membrane (kg) = (floor + upturns) × consumption per coat × coats × (1 + waste%)
Tape (m) = perimeter × 1.1 + 0.5 m per detail
Consumption per coat comes from the data sheet. It is usually stated as kg/m² for a set dry-film thickness. Two coats is the common minimum, applied at right angles.
Site tips
- Confirm the upturn height on the drawings. Showers often need full height, not 150 mm.
- Price flood testing as its own item. It takes time and water.
- Allow for falls to the drain. A membrane does not fix ponding.
Questions
How high should waterproofing go up the wall?
Common practice is 150 mm minimum on floors, and higher in shower zones. Use whatever the specification or local standard requires.
How many coats of liquid membrane do I need?
Most systems need at least two coats to reach the dry-film thickness on the data sheet.
Is reinforcing tape included in the coverage rate?
No. Tape, corners and pipe collars are separate items and are often missed in estimates.