How to Get Rid of Black Mould Before You Paint
Painting over live black mould is the most common mistake we hear about — and the most expensive. The mould stays alive under the new film, feeds on the fresh paint, and pushes back through within months, taking your afternoon's work with it. Kill it, clean it, dry it — then seal the surface with a black mould paint like Legacy™ Anti Mould Paint. Here's the full method we give our own customers, from the team that manufactures the paint in East Kilbride.
Why can't you just paint over it?
Mould isn't a stain — it's a living organism with roots (hyphae) that grow into the surface. Trap it under emulsion and you've given it a dark, sheltered environment with a fresh food source. Even under an anti mould paint, a thick layer of live growth can compromise adhesion, so the film doesn't bond properly to the wall. The fungicide in Legacy stops new spores germinating on the surface; it's not designed to kill an established colony sandwiched underneath it. Five minutes of prep is the difference between a job that lasts years and one that fails by Christmas.
The full removal method
Wear rubber gloves and ideally a basic FFP2 mask — disturbing mould releases spores. Open the window, close the door to the rest of the house, and lay an old sheet below the wall. Anyone with asthma or a compromised immune system should stay out of the room during cleaning.
Use a household mould and mildew killer or a diluted bleach solution on the affected area, extending well beyond the visible edge of the growth — the colony always extends further than you can see. Leave it to work for the time stated on the product, don't just spray and immediately wipe.
Wipe the dead growth away with a damp cloth and bin the cloth afterwards. Never dry-brush or sand live mould; that fires spores across the whole room. Stubborn speckling may need a second application before it wipes clean.
Go over the area with clean water to lift any cleaner residue, then let the surface dry fully — overnight is ideal, longer for cold rooms. Paint applied to a damp wall won't bond properly, and you'll have trapped the very moisture you're fighting. This is the step people rush, and it's the one that matters most.
Once clean and bone dry, apply Legacy™ with a brush or roller — two coats, letting the first dry fully. The in-film fungicide (batch-tested on every run at our factory) now makes the surface itself hostile to regrowth, so the cycle of scrub-and-return is broken for good.
When cleaning isn't enough
Being straight with you: this method is for condensation mould on paintable surfaces. If the plaster is soft, blowing or crumbling, if mould covers a very large area (the NHS suggests getting professional help for patches bigger than about a square metre), or if the wall is being fed by a leak or rising damp, cleaning and painting won't hold. Fix the water source or get the plaster repaired first — then Legacy will keep the new surface clear. And if mould keeps returning across an entire room despite good prep, the room has a ventilation problem worth solving alongside the paint (our guide on whether anti mould paint works covers what paint can and can't do).
Frequently asked questions
How soon after cleaning can I paint?
Once the surface is completely dry — typically the next day. In a cold or unventilated room, give it longer.
Do I need to remove the old paint?
No, only clean off the mould. Sound existing paint is a fine surface for Legacy. Scrape back anything flaking.
Will white vinegar work instead of mould killer?
It can kill surface growth, but it's slower and the smell lingers under paint. A purpose-made mould killer or diluted bleach does the job more reliably before painting.
Wall clean and dry? Seal it properly so you never do this job twice. From £32.99 with next-day delivery.
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