How to Remove Mould from Walls — Toronto Home Guide

Mould on walls is common in Toronto homes — particularly in bathrooms, basements, and exterior walls in winter where condensation forms. Surface mould (less than 10 square feet total) can be safely treated yourself. Larger infestations or mould that has penetrated drywall require professional remediation.

Safety First

• Wear gloves and an N95 mask before cleaning mould — disturbing it releases spores into the air
• Ventilate the room — open windows if possible
• Protect your eyes (mould cleaner splatter)

White Vinegar Method (Safest, Good for Light Mould)

1. Pour undiluted white vinegar into a spray bottle
2. Spray the mouldy area and let sit for 1 hour without wiping — the acid needs time to penetrate and kill the mould
3. Scrub with a stiff brush or scrub pad
4. Wipe clean with a damp cloth and allow to dry completely
5. Repeat if needed — vinegar kills about 82% of mould species

Hydrogen Peroxide Method (Effective, Colour-Safe)

1. Pour 3% hydrogen peroxide into a spray bottle (do not dilute)
2. Spray and let sit for 10–15 minutes
3. Scrub and wipe clean
4. Dry thoroughly

Hydrogen peroxide is safer than bleach for coloured walls — test in a hidden area first on painted surfaces.

Diluted Bleach (Most Effective, Non-Porous Surfaces)

1. Mix 1 cup of bleach in 1 litre of water
2. Apply with a cloth or sponge to the affected area
3. Allow to sit for 10–15 minutes
4. Rinse well and dry completely

Bleach is effective on tile, grout, and sealed concrete but won't kill mould that has penetrated porous surfaces like drywall — it bleaches the surface without reaching the roots. Never mix bleach with vinegar or ammonia.

After Cleaning — Preventing Return

• Find and fix the moisture source — mould returns without this step
• Common sources: condensation on cold exterior walls (improve insulation or ventilation), shower steam (run exhaust fan longer), roof or plumbing leaks
• In Toronto's cold winters, keeping indoor humidity below 50% prevents most mould growth on walls — use a dehumidifier or hygrometer to monitor
• Repaint with mould-resistant paint in bathrooms and basements

When to Call a Professional

• More than 10 square feet of mould
• Mould that has penetrated drywall (soft, discoloured, or crumbling drywall behind the surface mould)
• Mould in HVAC ducts
• Anyone in the home has respiratory conditions or is immunocompromised
• Mould returned after cleaning within 2–4 weeks