How to remove mould from walls and ceilings

Inspired by a helpful YouTube guide. This walk-through draws on the popular UK video "How to remove mould from walls and ceilings" from the Polycell UK channel. It is a clear, practical demonstration of how to treat and remove mould using a specialist mould killer — and it covers the crucial point that killing the spores matters as much as scrubbing the surface clean.

1. Protect yourself before you start

Mould spores become airborne when disturbed. Wear a dust mask — an FFP2 or FFP3 rated one if you have it — as well as gloves and eye protection. Open windows in the room, but close internal doors to avoid spreading spores to the rest of the house.

Old clothing is sensible too. Bleach-based treatments will spot whatever they touch.

2. Identify and address the moisture source

Before you clean anything, work out why the mould is there. Condensation mould — the most common type — forms where warm moist air meets a cold surface. It is most often seen in corners near external walls, around window reveals, and on bathroom ceilings.

Rising damp and penetrating damp both produce mould too, but the pattern is different. Rising damp starts at the base of walls and works up. Penetrating damp appears at irregular points usually linked to a specific weather direction or external fault. If you are not sure which you have, treat the visible mould and watch where it returns — the pattern tells you a lot.

3. Apply a mould killer

Use a proprietary mould killer spray — products like Polycell Mould Killer or HG Mould Spray are widely available and genuinely effective. Alternatively, dilute household bleach to around a 1:4 ratio with water in a spray bottle.

Spray the affected area generously. Allow the product to dwell on the surface for the time specified on the label — usually 5 to 15 minutes. The dwell time is when the active ingredient kills the spores. Wiping too quickly before it has done its job is one of the most common reasons mould comes straight back.

4. Scrub and rinse the surface

Using a stiff-bristled brush or an old sponge, scrub the mould firmly. Work from the edges of the affected area inward to avoid spreading spores outward. Rinse the surface with clean water and then wipe dry with old cloths or paper towels, which go straight in a bin bag.

Dispose of the brush or sponge afterwards — do not reuse them around the house. On emulsion-painted walls, the colour may lift slightly where the mould has colonised — that is normal and the surface will need repainting once fully dry.

5. Allow the surface to dry thoroughly

Mould will return quickly onto a damp surface, so drying is essential. Leave windows open, run an electric heater, or use a dehumidifier to dry the wall out. In a bathroom, this might mean leaving the extractor fan running for several hours after treatment.

Do not paint over a damp surface. If the wall feels cold or the paint bubbles after a test patch, give it more time. Patience here saves repainting sooner than you would like.

6. Apply mould-resistant primer and paint

Once the surface is completely dry, apply a coat of mould-resistant primer before repainting. On bathroom ceilings in particular, use a paint formulated with anti-mould additives — most major paint brands have them as a standard product.

This does not prevent mould permanently if the conditions remain, but it does slow the regrowth considerably and makes future cleaning easier.

7. Improve ventilation to prevent it returning

For condensation mould, ventilation is the long-term solution. Opening windows after showering, cooking, or drying clothes indoors makes a real difference. A bathroom extractor fan with a humidistat sensor — one that runs until the moisture level drops rather than switching off with the light — is one of the most effective changes you can make.

Keeping furniture a few centimetres away from external walls helps air circulate at the cold spots where mould typically starts. It is a small adjustment with a noticeable effect over winter.

When to call a handyman

Call Richard if the mould is widespread across multiple rooms, if it keeps returning despite cleaning and ventilation improvements, if you suspect rising or penetrating damp is the cause, or if the mould is behind plasterboard. At that point the surface treatment alone will not fix it.