Positive-Side & Negative-Side Basement Waterproofing

A basement that has been waterproofed before and is still not dry usually has one of three problems: the water was treated from the wrong side, the original system was not continuous, or the water is coming from somewhere the first repair never addressed.

The first question is which side the water is on. Positive-side waterproofing is applied to the outside face, where it meets the water first. Negative-side systems are applied inside, on the face the water reaches after it has entered the structure. Both can work, but they are not interchangeable.

Positive-side systems — membranes, coatings and drainage boards — are the more reliable option where the outside can be excavated. They keep water out of the concrete rather than resisting it from within, and they can be inspected. The constraint is access: on an existing building, excavation may be impractical or too costly.

Negative-side systems — crystalline coatings, cementitious tanking and injection — are used where the outside is inaccessible. They can stop water entering the occupied space, but they work against the pressure, so they depend on sound concrete, correctly treated joints and cracks, and a system that is allowed to cure properly.

We start with a moisture survey and a close look at the junctions, because a basement that is wet at the wall-floor joint is a different problem from one that is wet across the whole wall. Then we specify the side, the system and the drainage together, and we say what the repair can and cannot be expected to achieve.