Tanking vs cavity drain membrane
Tanking holds water back with a barrier on the wall. A cavity drain membrane lets water through the wall and drains it away behind the membrane to a sump. For a wet basement, the membrane is the safer choice.
Free, no obligation. One local company prices it, not five.
- €50 to €180a m² for either
- €3,000 to €12,000membrane with a sump
- Type Abarrier: tanking
- Type Cdrained: membrane and sump
How they compare
| Tanking (Type A) | Cavity drain membrane (Type C) | |
|---|---|---|
| How it works | Holds water back with a slurry or bonded membrane | Lets water through, drains it to a sump |
| Suits | Sound walls, little water | Wet basements, old stone and brick |
| Water pressure | Has to resist it | Doesn't fight it |
| Needs a pump | No | Yes, with a yearly service |
| If it fails | Hard to find the leak | Water still drains to the sump |
| Wall prep | Clean, sound surface | Less, fixed with sealed plugs |
Many conversions use both: a membrane on the walls and floor, and tanking where a membrane can't go. The waterproofing designer picks the mix for your basement.
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Questions we get asked
Which is better, tanking or a membrane?
For a basement that gets wet, a cavity drain membrane with a sump. For a dry basement with sound walls, tanking can be enough.
Does a cavity drain membrane need maintenance?
The membrane doesn't. The sump pump does: a yearly service and a back-up.
Can you plaster over a membrane?
Yes. It's usually covered with plasterboard on battens, or a mesh-faced membrane that takes plaster.
What's BS 8102?
The code of practice for protecting below-ground structures against water. It sets out Types A, B and C, and the grades of dryness a room needs.
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