Tanking | Chalkline

Tanking is applying a continuous waterproof membrane to fully enclose a structure so it holds back water, the way a tank holds water in. Its classic use is below-ground work where the structure sits in, or periodically below, the water table and the membrane has to resist hydrostatic pressure (the push of standing water) rather than just shed rain (verified 2026-05-25, general construction usage).

Where it is used:

Below-ground: basements, lift pits, retaining walls, planter boxes. The whole structure is wrapped, under the slab and up the walls, so water cannot find a path in.
Wet areas: on Australian sites the word is also used loosely for fully waterproofing a shower or bathroom, turning a continuous membrane up the walls to form a watertight tray (“a tanked shower”).

The standards angle:

Domestic wet-area waterproofing is governed by AS 3740. That is the right standard for the “tanked shower” sense.
External above-ground membranes sit under AS 4654 (materials in Part 1, design in Part 2).
True below-ground tanking (basements under hydrostatic head) is a specialised design area not fully covered by the residential wet-area standards, so it usually follows the membrane manufacturer’s system and engineering input.

For a builder:

Match the membrane to the load: a shower membrane is not a basement tanking system. Below-ground work faces constant water pressure and needs a system rated for it.
Tanking is continuous by definition. A break at a penetration, junction, or upturn is where it fails, so detailing matters more than the flat areas.

Also known as: tanked, structural waterproofing, below-ground waterproofing.

Related

See also

Related articles