What should I do if I find mould during my Calgary basement renovation?

If you discover mould during a Calgary basement renovation, stop all demolition work immediately to avoid spreading spores through the air, and assess the extent before deciding on next steps. Small patches under 10 square feet on surface materials can often be handled by a knowledgeable homeowner, but anything larger, anything behind walls that suggests a systemic moisture problem, or any mould on structural materials requires professional remediation.

The first priority is identifying the moisture source that caused the mould, because removing mould without fixing the water problem guarantees it comes back. In Calgary basements, the most common culprits are foundation wall cracks that admit spring snowmelt (especially after rapid chinook-driven melting over frozen ground), failed or clogged weeping tiles (common in 1960s-1980s homes with original clay weeping tiles), condensation from improper insulation (fiberglass batt insulation placed directly against cold concrete without a rigid foam thermal break), and insufficient exhaust ventilation in bathrooms. Bentonite clay soils prevalent throughout Calgary's NW and NE quadrants expand when wet and press water against foundation walls through hairline cracks that are invisible from the interior.

For small mould patches (under 10 square feet on non-structural surfaces), you can clean the affected area yourself. Remove and discard any mouldy drywall, insulation, and carpet — these materials cannot be effectively cleaned and must be thrown out. Clean hard surfaces (concrete, wood framing) with a solution of unscented detergent and water, then allow to dry completely. Wear an N95 respirator, gloves, and eye protection during any mould disturbance. Seal off the work area with plastic sheeting and run a negative air setup (even a box fan exhausting through a window) to prevent spores from spreading to the rest of the house.

For larger mould contamination, mould on structural framing, or any situation where the mould source is unclear, hire a professional mould remediation company. Calgary remediation costs typically range from $2,000-$8,000 for a section of basement wall to $10,000-$25,000 for extensive contamination involving multiple walls or the subfloor area. Professional remediators set up full containment with HEPA-filtered negative air machines, remove all affected materials, treat structural members, and provide clearance testing to confirm spore counts have returned to normal levels.

Before refinishing, address every contributing moisture issue. Repair foundation cracks through epoxy or polyurethane injection ($250-$700 per crack), replace failed weeping tiles, install or upgrade the sump pump system ($600-$1,800), and rebuild walls with moisture-appropriate insulation — closed-cell spray foam or XPS rigid board with proper vapour barrier. Test the space with a humidity monitor for at least one full spring snowmelt season before re-finishing if the mould was moisture-related. Also test for radon while the basement is open, since Calgary is in a high-radon zone and mitigation is far easier before walls go back up.

Mould remediation and the subsequent renovation both require City of Calgary building permits, and all work must pass inspection by a Safety Codes Officer. If you need help finding remediation specialists or basement contractors experienced with moisture-damaged basements, reach out through Calgary Basement Remodeling for a free match.