How to Remove Mould from Walls and Ceilings — Toronto Home Guide

Surface mould on painted walls and ceilings — typically appearing as black, grey, or green spots or patches — is common in Toronto homes, particularly in bathrooms, basement walls, and exterior-facing walls. Surface mould that appears on a painted surface can usually be cleaned; mould that has penetrated drywall or is associated with a water leak may require professional remediation.

Safety First

• Wear gloves and a face mask (N95 or better) when cleaning mould — mould spores become airborne when disturbed and are a respiratory irritant
• Ventilate the area: open windows and use a fan directing air out of the room
• If the mould patch is larger than roughly one square metre (about a 1m × 1m area), or if you suspect mould is behind the wall, consult a professional — Health Canada recommends professional assessment for large mould problems

White Vinegar Method (Recommended for Most Surfaces)

1. Pour undiluted white vinegar into a spray bottle
2. Spray the affected area and allow to sit for 1 hour — do not rinse immediately; the vinegar needs time to kill the mould
3. Scrub with a stiff-bristle brush or sponge
4. Wipe clean with a damp cloth and allow to dry thoroughly
5. Repeat if necessary for stubborn patches

Bleach Method (For White/Light Surfaces)

1. Mix 1 tablespoon of bleach per cup of water in a spray bottle
2. Spray onto the mould and allow to sit for 10–15 minutes
3. Scrub with a brush and wipe clean
4. Rinse with clean water and allow to dry thoroughly
5. Note: bleach discolours painted surfaces and should only be used on white or light-coloured painted walls; vinegar is safer for coloured surfaces

Drywall vs Painted Surfaces

• Surface mould on painted drywall can be cleaned with the above methods
• If the drywall is soft, stained through, or the mould returns within weeks despite cleaning and ventilation improvements, the drywall has been compromised and must be replaced
• Bathroom tile and grout: use bleach solution; allow to penetrate deeply into grout before scrubbing

Preventing Recurrence

• Mould requires moisture — fix the source of moisture first; painting over mould without addressing the moisture source always fails
• Increase ventilation: bathroom exhaust fans, dehumidifiers in basements, opening windows when weather permits
• Use mould-resistant paint (available at hardware stores) when repainting affected areas