How do Toronto drywall contractors handle mould remediation before installing new drywall in a damaged basement?

Most professional drywall contractors in the GTA will not begin installing new drywall until mould remediation is fully completed and the space has been cleared, either by a dedicated remediation company or by the contractor's own qualified crew for smaller-scale issues. Understanding the process helps you plan the timeline and budget for your basement project and ensures the new drywall goes up in a clean, dry environment.

The first step is always assessment and testing. Before any demolition begins, a professional should determine the extent of the mould contamination. Surface mould on a small section of drywall is very different from mould that has spread into the wall cavity, saturated the insulation, and colonized the wood framing. For larger areas (generally anything over 10 square feet), many GTA contractors recommend hiring an independent environmental consultant to take air quality samples and identify the mould species. This baseline testing, which typically costs $300 to $800 in the GTA, establishes what you are dealing with and provides a benchmark for clearance testing after remediation.

Containment is critical. Professional remediation begins by isolating the work area from the rest of the home using 6-mil polyethylene sheeting taped to the ceiling, walls, and floor to create a sealed enclosure. A negative air machine with HEPA filtration runs continuously during the work, pulling air from the containment zone and exhausting it outside through a duct. This prevents mould spores from spreading to unaffected areas of the home — a step that many homeowners do not realize is necessary but that makes the difference between solving the problem and spreading it throughout the house. GTA remediation companies typically charge $500 to $1,500 just for containment setup depending on the area size.

The next phase is removal of contaminated materials. All mould-affected drywall must be cut out and removed — it cannot be cleaned, dried, or treated and reused. Professional practice requires cutting back at least 600mm (about two feet) beyond the visible mould boundary, because mould growth often extends behind the drywall surface where it is not visible. The drywall is cut into manageable sections, double-bagged in heavy plastic, and disposed of as contaminated waste. Insulation behind the affected drywall is removed entirely, as fibreglass and batt insulation that has been exposed to moisture and mould cannot be salvaged. Workers wear full PPE including N95 respirators, Tyvek suits, and gloves throughout the process.

Framing treatment follows removal. Wood studs and plates that show mould growth are wire-brushed or sanded to remove surface contamination, then treated with an antimicrobial solution. If structural framing is soft, rotted, or compromised, it must be sistered or replaced — this is more common in older GTA basements where moisture has been an ongoing issue for years. The concrete foundation wall behind the framing is also inspected and treated. Any active water entry points — cracks, seeping joints, failed waterproofing — must be repaired before the wall is rebuilt.

Drying and clearance is the phase most homeowners want to rush through, but it is essential. The remediated area must be thoroughly dried using commercial dehumidifiers and air movers, typically for 48 to 72 hours, until moisture readings in the framing and concrete are within acceptable levels (typically below 16% moisture content in wood framing as measured by a pin-type moisture metre). After drying, clearance testing by the independent environmental consultant confirms that airborne mould spore counts have returned to normal levels. Only after clearance should new drywall work begin.

New drywall installation after remediation should include upgrades that prevent recurrence. Smart GTA contractors will recommend mould-resistant (purple board) drywall at $24 to $32 per sheet instead of standard paper-faced board, proper R-20 insulation with a continuous 6-mil polyethylene vapour barrier sealed at all seams and penetrations, and addressing any ventilation deficiencies in the basement. The complete process — from initial assessment through remediation, drying, clearance, and new drywall installation — typically takes two to four weeks for a standard GTA basement and costs $3,000 to $12,000 depending on the extent of contamination.

Important note on scope boundaries: drywall contractors handle the drywall work, but dedicated mould remediation is a separate trade requiring different insurance, training, and WSIB coverage. Some larger GTA companies offer both services, but many homeowners hire a remediation company first, then bring in a drywall contractor after clearance. Toronto Drywall Installers can help you find drywall professionals experienced in post-remediation basement work through the Toronto Construction Network.