Below-Grade & Basement Waterproofing

A basement that floods is not just an inconvenience — it is a structural problem in progress. Water entering below grade brings with it soil particles, chlorides, and other aggressive agents that can undermine the foundation over time. The pressure that pushes water through a basement wall is not a trickle; it is the full weight of the water table acting on every square metre of the wall, and it will find the weakest point — a construction joint, a crack, a poorly sealed pipe penetration — and force its way through.

The first step in any basement waterproofing project is to determine which side of the wall the water is coming from. A positive-side system is applied to the outside of the wall, where the water pressure is, and it is always the preferred solution because it stops the water before it enters the structure. A negative-side system is applied to the inside face, and it is used when the outside of the wall is not accessible — for example, when the basement is already built and the surrounding soil cannot be excavated.

For new construction we recommend positive-side sheet membranes or liquid-applied systems bonded to the outer face of the foundation wall, protected by a drainage board that carries groundwater down to the perimeter drain. For existing basements, we use negative-side cementitious coatings and crystalline systems that penetrate into the concrete and block the water paths from the inside. In both cases, the detailing at the wall-to-floor junction, the lift pit, and the pipe penetrations is where the system is won or lost.

We also look at the drainage around the building. A perimeter drain that is blocked, a downpipe that discharges against the wall, or a garden that slopes towards the foundation can all push water against the structure. We address these sources as part of the same project, because a waterproofing membrane alone cannot fight a continuous supply of water that is being directed at the wall.

The result is a basement that stays dry through the heaviest rains, with the structure protected from the long-term damage that water ingress causes. We document the full system, provide a written specification, and stand behind the work with a warranty. If the basement floods again, we will come back and find out why.