Waterproofing Cost in Markham

Dig a trench along the exterior foundation wall, 3-4 feet wide and down to the bottom of the footing (typically 6-8 feet below grade). In Toronto clay, this is usually stable enough to excavate without shoring, but sandy soil or deep excavations (8+ feet) require trench boxes or sloped banks to prevent collapse. You MUST locate underground utilities (gas, water, electrical, telecom) before digging — call Ontario One Call at least 5 days before starting.

Pressure-wash the foundation to remove dirt, old tar, and loose concrete. Inspect for cracks and patch them with hydraulic cement or polyurethane injection (flexible sealant that moves with the crack). Concrete surfaces must be clean and dry before membrane application — water or oil contamination prevents the membrane from bonding.

Roll or spray a rubberized waterproofing membrane onto the foundation wall, from footing to grade. Common products: Blueskin, Bituthene, or liquid-applied membranes like Tremco or SealBoss. The membrane must overlap seams by 3-4 inches and seal around penetrations (sewer pipes, electrical conduits). Thickness: 60-80 mils for most residential applications. Thicker membranes (120+ mils) are used below-grade in high-water-table areas.

Lay 4-inch perforated Big-O pipe (or rigid PVC with holes) at the base of the footing, sloped 1/4 inch per foot toward the sump pit or daylight outlet. Wrap the pipe in filter fabric (geotextile sock) to prevent silt from clogging the perforations. Surround the pipe with 12-18 inches of 3/4-inch clear gravel. Do NOT use limestone screenings, sand, or crusher dust — fine particles clog the system. The gravel acts as a drainage layer; water flows through it into the pipe.

Install dimpled drainage board (e.g., Delta-MS, Tremco TremDrain) over the waterproofing membrane. The dimples create an air gap and drainage path; water that reaches the membrane can flow down to the weeping tile instead of sitting against the foundation. Backfill with gravel for the first 2-3 feet (maintains drainage), then switch to clay fill near grade (slopes water away from the house). Compact the fill in 12-inch lifts to avoid settlement.

If the weeping tile drains to an interior sump pit, install a 1/2 HP or 3/4 HP submersible pump with a check valve (prevents backflow) and a discharge line that runs to the street, storm sewer, or at least 10 feet from the foundation. The sump pit should be 18-24 inches deep with a gravel base for drainage. Many homeowners add a battery backup pump in case of power failure during storms.

Slope the soil away from the foundation at 5-10% grade for the first 6-10 feet. Use the formula D = G × L to calculate the drop: for a 10-foot slope at 5% grade, that's 0.05 × 10 = 0.5 feet (6 inches of drop). Extend downspouts at least 6 feet from the house (or tie them into underground drainage pipes that discharge away from the foundation). For patios adjacent to the house, slope them 1-2% away from the foundation. Swales (shallow V-shaped ditches) along property edges channel heavy runoff at 1-10% slope. Surface water is often the biggest contributor to basement moisture — fixing grading costs $1,000-$3,000 and often solves 80% of the problem, but most people skip it because it's not glamorous.