Basement tanking
Tanking is the traditional way to keep water out of a cellar or basement: a waterproof barrier applied to the inside (or occasionally the outside) of the walls and floor. This page explains how it works, when it is suitable and what to ask a specialist. BasementBridge is an introduction service, not a contractor.
What is basement tanking?
Under BS 8102:2022, tanking is Type A barrier protection. Common materials include:
- Cementitious slurry brushed or sprayed onto prepared masonry in several coats
- Waterproof renders with additives that resist water penetration
- Bitumen or polymer coatings and bonded sheet membranes
The barrier works by resisting water pressure. That makes surface preparation critical: loose render, salts and cracks need to be dealt with first, and the barrier must be continuous, including at the joint between wall and floor.
When tanking is a good fit
Tanking tends to suit sound, stable masonry where water ingress is limited, for example dampness through the walls rather than running water. It adds very little thickness to the wall, which can matter in a cellar with limited space. It is also often used as part of a combined system, with a cavity drain membrane providing a second line of defence.
Limitations to be aware of
Because tanking holds water back, any crack, gap or movement in the structure can let water through, and a failed barrier is hard to repair without stripping it. Fixings driven through the tanking, such as shelves or sockets, need care. Where there is significant water pressure or a high water table, specialists often recommend drained (Type C) protection instead or as well. Our cavity drain membrane guide compares the two.
Tanking versus cavity drain membranes
| Tanking (Type A) | Cavity drain (Type C) | |
|---|---|---|
| How it works | Blocks water with a barrier | Lets water drain behind a membrane to a sump |
| Best suited to | Sound walls, limited water | Wetter conditions, habitable conversions |
| Maintenance | Little, but hard to repair | Pump servicing; system can be inspected |
| Space taken | Minimal | A few centimetres plus wall finishes |
How much does tanking cost?
Cost depends on area, preparation and access. Published UK guides suggest indicative figures per square metre, which we summarise in our waterproofing and tanking cost guide. Only a survey of your property can give a real price.
Questions to ask a tanking specialist
- Is tanking right for my water conditions, or would a drained system be safer?
- What preparation will the walls need?
- What guarantee is offered, and is it insurance-backed?
- How should I fix things to the walls afterwards?
- Will the design follow BS 8102:2022, and will I get a written specification?
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