How Does Anti Mould Paint Work?

People ask us this a lot, usually after they've already tried scrubbing a wall three times and the spots came straight back. Fair question — if you're about to spend £30-odd on a tin, you probably want more than "it just works." So here's the actual mechanism behind Legacy™ Anti Mould Paint, explained the way we'd explain it to a customer who rang our East Kilbride factory and asked us straight.

What's actually different about the paint film?

Start with what mould needs. A spore lands on a surface, and if there's moisture, a food source, and no resistance, it germinates and starts spreading. Ordinary emulsion gives it all three — the dried film holds a bit of surface moisture, household dust and skin cells sitting on top provide the food, and there's nothing in the paint to stop growth once conditions are right.

Anti mould paint changes one of those three variables. We mix a fungicide into the wet paint during manufacture — not sprayed on afterwards, not a coating over the top, but blended right through the base before it's ever tinned. As the paint dries and the film cures, that fungicide sets throughout the whole thickness of the layer, not just the top skin. That matters, because it means the protection isn't a one-off surface treatment that wears away after a few cleans.

We check the fungicide loading on every batch before it leaves the factory. It's the one part of the process where you genuinely can't eyeball it and hope for the best — too little and you've made expensive white emulsion, which does nobody any favours.

Why does it stop mould rather than just resist water?

This is where people mix up two different jobs. A water-resistant or wipeable paint keeps liquid from soaking into the wall — useful, but it does nothing biologically. Mould doesn't need standing water; it needs humidity, and most UK bathrooms sit above the roughly 75% humidity threshold that Aspergillus niger (the usual culprit behind black spot mould) needs to get going, every single time someone showers.

A fungicidal film works on the biology, not just the moisture. When a spore lands and starts to germinate, it comes into contact with the biocide in the film and the growth is stopped before it can establish a colony. That's the whole difference between a paint that survives a damp room and one that defends it.

Does the protection wear off?

Not in the way a surface spray would. Because the biocide is distributed through the film rather than sitting on top of it, normal wear — wiping the wall down, light abrasion, years of steam — doesn't strip the protection away in one go. What does undermine it is painting over the top with a standard, non-fungicidal emulsion, because then the exposed surface mould actually touches is the new layer, not the protected one underneath. We've written more on that trade-off in our guide on painting over anti mould paint, since it's a genuinely common question.

Coverage-wise, Legacy goes down at roughly 12m² per litre, touch dry in 1-2 hours and ready for a second coat after about 4. Two coats matter here more than people expect — a single thin coat leaves patches where the film is too sparse to give full biocide coverage, and mould is opportunistic enough to find them.

Is this the same as "anti-condensation" paint?

No, and it trips a lot of people up. Anti-condensation paints usually work by insulating the surface slightly, so the wall doesn't get quite as cold and moisture is less likely to condense on it in the first place — a physics fix. Anti mould paint is a biology fix: the moisture might still form, but nothing can grow in it. They're solving different halves of the same problem, and we've gone into more depth on which one actually fits your situation in anti condensation paint vs anti mould paint.

Frequently asked questions

Is the fungicide only on the surface of the paint?
No — it's mixed through the wet paint before application, so it's distributed through the whole dried film, not just a thin top layer.

Will it work straight away, or does it need to "activate"?
Once the paint is touch dry the film is doing its job. There's no separate curing or activation stage to wait for beyond normal drying.

Does one coat give partial protection?
It'll do something, but we wouldn't rely on it. Thin patches in a single coat are exactly where mould finds a way in — two coats is what we recommend and test against.

Can the fungicide run out over time?
In normal domestic use, no — it's not a treatment that gets "used up" by contact with spores the way, say, a mould killer spray is consumed. It degrades the way any paint film eventually does, through age and wear.