Mold growing on walls or ceiling
easy 1–3 h
Tools: N95 respirator, gloves and goggles, spray bottle, scrub brush or sponge, bucket, hygrometer, fan · Materials: detergent or a mould cleaner (not bleach on porous surfaces), mould-resistant primer and paint, weatherstripping or a timer switch for the bathroom fan
Steps
- Measure the patch: scattered spots under about 1 m² (10 sq ft) on paint or tile you can clean yourself; more than that, or mould inside a wall, is remediation work.
- Find the moisture: condensation on a cold outside wall or window, a bathroom without a working fan, a leak above, or furniture pushed tight against an exterior wall.
- Wearing a respirator and gloves, wash the area with detergent and water or a mould cleaner, and let it dry completely with a fan; bleach whitens but does not reach into plaster or drywall.
- Fix the cause before repainting: run the bathroom fan 20 minutes after showers, keep the room above 16 °C (60 °F), pull furniture 5 cm off the wall, and dry laundry elsewhere.
- Once dry, prime with a mould-resistant primer and repaint; painting over damp or unwashed mould brings it back within weeks.
- Check the room's humidity with a hygrometer — keeping it under 60 % is what stops regrowth.
Stop and call a pro if
- the mould covers more than about a square metre, is fuzzy and black, or comes back within weeks of cleaning
- the drywall is soft, stained through or bulging — the moisture is inside the wall
- anyone in the house has asthma, allergies or a weak immune system
- there is a leak from above or behind that you cannot find
What a pro does that you can't
A mould remediator removes contaminated drywall under containment and treats the framing, and a plumber or roofer fixes the leak; a handyman fits the fan, timer and insulation that stop condensation.
DIY cost: $15–50 in cleaner, primer and paint