Leaking basement

First, find out where it comes from

Leaks in a basement have three different origins and three different treatments: a through-crack conducting water, an unsealed construction joint, or diffuse absorption through a porous surface.

They can be told apart by the pattern of dampness: point-like and concentrated in the first case, linear along a fairly constant level in the second, extensive and uniform in the third. Getting the diagnosis wrong means applying the right product at the wrong spot.

Stage one: stop the moving water

No coating adheres to a substrate with water running across it. Active leaks are plugged with fast-setting expanding cementitious mortars, which cure within seconds and even under water, or with single-component polyurethane resins injected into the crack, which on contact with water develop an expanding foam up to forty times their volume.

Stage two: seal permanently

Polyurethane foam is a plug, not a permanent seal: it stops the water but lacks lasting elasticity. Once the crack is dry, a second injection follows with a low-viscosity two-component resin, which penetrates deep and cures soft-elastic, bonding to the crack walls.

Stage three: waterproof the surface

The repaired substrate is then coated with a penetrating crystalline slurry or a two-component osmotic slurry, both capable of working against negative pressure. The wall-to-floor junction is finished with a fillet in multi-purpose mortar: it is the point where most badly executed repairs leak again.