On a foundation wall the positive side is the soil face. A membrane there keeps water out of the concrete entirely, uses water pressure to press the membrane onto the wall, and protects the reinforcing steel. It requires access during construction, either by excavating around the wall or by installing blindside before the pour. Most sheet and fluid membranes are designed for positive-side use.
Positive side is backfilled already, so we're stuck with crystalline on the inside face.
Where it is possible, positive-side waterproofing is always the first choice; negative-side work is a fallback when access is gone.
Also heard as
- positive-side waterproofing
- wet side
Do not mix it up with
- Negative side: Negative-side waterproofing goes on the dry interior face and fights water pressure instead of using it.
Related terms
Negative side
The interior face of a wall or slab, opposite the water, where waterproofing must resist water pushing it off.
Blindside
Waterproofing installed on the shoring or soil face before the wall is poured against it.
Hydrostatic pressure
Pressure from standing groundwater against a wall or slab, rising with the depth of water above that point.
Fluid-applied membrane
A liquid waterproofing applied by roller, squeegee or spray that cures into a continuous rubbery film with no laps.