Damp and mould on walls: what to do before you paint

Updated 20 October 2026

Paint over mould and it comes back within weeks. Find the cause first, then clean, then paint.

Find the cause

• Black spots in corners and behind furniture, worse in winter: condensation. Air the room every day and heat it more evenly.
• A patch that grows after rain: water getting in from outside, such as a roof, a gutter or a crack.
• A tide mark low on the wall: damp rising from the ground.
• A patch under a bathroom or near pipes: a leak. Call a plumber first.

Clean it

1. Open the windows, and wear gloves and a mask.
2. Use a mould remover, following the label. Never mix bleach with other cleaners.
3. Let the wall dry completely, at least a day.

Then paint

1. Put an anti-mould primer on the area.
2. Finish with an anti-mould paint made for kitchens and bathrooms.

Call a painter if

• The area is bigger than about a square metre.
• The plaster crumbles or bubbles.
• It comes back after you’ve fixed the airing.

Need someone today? Dashfixe matches you with a vetted local artisan who is free now, and you approve the price before they travel.