Step-by-Step: How Interior Basement Waterproofing Works

This is the professional-grade process used by Canada Waterproofers on every interior waterproofing project across the GTA.

Step 1: Full Basement Assessment

Every project begins with a thorough inspection. Our technicians evaluate the source and pattern of water intrusion — whether it's coming through wall cracks, the floor-wall joint, the floor itself, or via a failed exterior drainage system. This assessment determines the exact scope of work and ensures we're solving the actual problem, not just masking symptoms.

Step 2: Crack Injection

Any visible cracks in poured concrete or block foundation walls are addressed before drainage work begins. We use polyurethane or epoxy injection systems to fill cracks under pressure, creating a flexible, waterproof seal that bonds permanently to the concrete. Polyurethane is preferred for active leaks (it expands to fill voids), while epoxy is better suited for structural cracks requiring rigidity.

Step 3: Interior Trench Excavation

This is where the main work happens. A trench is cut around the interior perimeter of the basement, approximately 12–15 inches wide, through the concrete floor. Around 10–12 inches of soil beneath the slab is removed. Small weep holes are drilled at the base of the foundation wall to allow water trapped inside the wall cavity to drain into the trench.

This step is labour-intensive but highly controlled — all debris is removed from the home, and the living space above remains largely undisturbed.

Step 4: Weeping Tile Installation

A new perforated weeping tile drain (modern high-capacity pipe) is laid at the base of the trench. This system collects groundwater, wall seepage, and hydrostatic pressure runoff and channels it toward the sump pit. In GTA homes with older clay-based weeping tile (common in pre-1980s construction), this step replaces a system that may have collapsed, cracked, or become blocked with silt and root intrusion.

Step 5: Drainage Membrane Installation

A dimple-board drainage membrane is installed along the interior face of the foundation wall, from the footing up. This membrane creates a gap between the wall and interior space, allowing any water that penetrates the foundation to drain downward into the weeping tile rather than entering the basement. High-quality membranes used in Canadian climate applications are engineered to handle freeze-thaw cycling without cracking or losing adhesion.

Step 6: Gravel Backfill

The trench is filled approximately three-quarters full with clean, clear gravel (typically ¾" clear stone). Gravel provides rapid drainage and prevents soil compaction over the weeping tile — a critical detail often overlooked in inferior installations. The gravel also helps distribute hydrostatic load evenly along the drainage system.

Step 7: Sump Pump Installation

A sump pit is installed at the low point of the drainage system, and a professional-grade sump pump is fitted to evacuate collected water from the home. Canada Waterproofers installs properly sized pumps with battery backup systems — a critical feature in the GTA, where summer storms that overwhelm drainage systems often coincide with power outages.

The discharge line runs water safely away from the foundation, following Ontario Building Code standards.

Step 8: Concrete Restoration

The trench is topped with freshly poured concrete, floated level with the existing floor. Once cured, the basement is clean, functional, and ready for use — with an invisible drainage system working beneath it.

Step 9: Vapour Barrier Application (Where Applicable)

In basements with elevated humidity or moisture migration through the floor, a heavy-duty polyethylene vapour barrier may be installed across the walls and/or floor. This prevents residual moisture from affecting air quality and protects any future finishes — drywall, framing, flooring — from moisture damage.