How do I remove mould from painted walls?

Treating mould on painted plaster without spreading spores, and how to redecorate so it does not come back through.

Difficulty: beginner
Time: 1 hr
Read: 2 min
Safety: caution

Short answer

Wet the mould before touching it, wipe with a mould remover or dilute bleach, let it dwell fifteen minutes, then wipe clean and dry the wall thoroughly. Do not paint over it — treat, dry fully, then use an anti-mould primer before repainting.

Mould on a painted wall is feeding on the paint, dust and moisture. The paint layer means the growth is mostly on the surface, which makes it easier to remove than mould in plaster or sealant — but only if you deal with the damp that put it there.

Safety

Never mix bleach with ammonia-based or acidic cleaners. Open a window and wear gloves. Disturbing dry mould sends spores into the air, so always wet it first. If mould covers more than about a square metre or keeps returning, get the cause assessed rather than repeatedly treating the symptom.

What you'll need

Mould remover or household bleach
Rubber gloves
Disposable cloths
FFP2 mask (optional)
Anti-mould primer for redecorating

Step by step

Open a window and put gloves on.Ventilation matters more than speed here.
Mist the affected area with water or mould remover before touching it.Wetting stops spores becoming airborne when you wipe.
Apply mould remover, or one part bleach to four parts water, and leave fifteen minutes.Contact time kills the growth. Wiping immediately just smears it.
Wipe with a disposable cloth, working from the outside of the patch inwards.Working inwards avoids spreading spores onto clean paint.
Bin the cloths straight away rather than washing them.Washing transfers spores to the machine and everything washed after.
Dry the wall completely with a fan or an open window.Residual moisture restarts the growth within days.
Before repainting, apply an anti-mould primer and let it cure.Painting over untreated or damp mould means it grows through the new emulsion within weeks.

Tips

Mould in the same corner every winter is a cold-bridge and ventilation problem, not a cleaning problem. Moving furniture off the wall often solves it permanently.
Bleach whitens mould stains on paint but may leave a discoloured patch — expect to repaint the area.
A cheap hygrometer tells you whether you have a genuine humidity problem. Below 60% relative humidity, mould struggles to establish.

Common mistakes

Painting over mould — It grows through emulsion within weeks and you have sealed damp into the wall.
Wiping dry mould — Spores go airborne throughout the room.
Treating the wall but not the moisture — Guarantees it returns, usually in the same spot within a month.

Questions people ask

Can I just paint over mould with anti-mould paint?

No. Anti-mould paint inhibits new growth on a clean, dry surface — it does not kill existing mould underneath. Treat, dry, prime, then paint.

Why does mould keep coming back on the same wall?

That wall is colder than the rest of the room, so moisture condenses there first. It is usually an external corner, a spot behind furniture, or a cold bridge in the structure.