Anti-mould paint: when it helps and when it hides the problem

Does anti-mould paint work?

It works as a brake, not a cure. Anti-mould paint contains biocides — substances that make it harder for fungi to grow on the paint film. If the wall keeps surface humidity above ~80% for days, the mould eventually comes back: sometimes it takes a winter instead of three weeks, but it comes back.

In other words, paint makes sense after the cause has been dealt with, as extra protection at the coldest spots. Painted over an active problem, it hides it for a few months and delays the diagnosis. Before buying tins, check with the free diagnosis whether the pattern is condensation, rising damp or water ingress.

Anti-mould paints and sprays are biocidal products, covered by EU Regulation 528/2012. Use biocides with care. Always read the label and product information before use.

When anti-mould paint helps

• Condensation already under control: you've aired, switched on the extractor fan and brought morning humidity down to 55–60%, but one cold corner still picks up black specks now and then.
• Bathrooms and kitchens, where there are daily vapour peaks even with good ventilation. See damp in a bathroom without a window.
• Ceilings next to external walls in uninsulated buildings from the 1960s–80s, where the thermal bridge can't be fixed without building work. See mould on the ceiling.
• Behind wardrobes against cold walls, after moving them 5–10 cm away.

In these cases paint buys you margin: mould takes longer to appear and the next clean is easier. About 70% of Portugal's housing stock was built before thermal insulation rules, which date from 1990, so cold walls are the rule rather than the exception. Paint helps on those walls — always as a complement.

When paint hides the problem

Be wary of "anti-damp painting" proposals for ground-floor stains with salt deposits. Many companies offer a free visit and sell their own system — the diagnosis and the work come from the same source. A second opinion before paying costs less than repainting twice.

How to choose an anti-mould paint: what to read on the label and spec sheet

There's no "best brand" that suits every wall. What separates a suitable paint from an unsuitable one is written on the label and the spec sheet — you just need to know what to look for.

• Intended use: interior, and for which rooms (bathroom, kitchen, bedrooms). Some are meant only for utility areas.
• Compatible surface: cement render, plaster, plasterboard or lime plaster. A paint designed for cement may not suit an old wall.
• Vapour permeability: on walls that need to dry out, choose paints that let vapour through.
• Coverage rate (m² per litre per coat) and number of coats — that's what determines how much paint you need, not the size of the tin.
• Drying and recoating times, and how long to air the room before using it again.
• Active substances listed on the label, with the warnings and precautions for use.
• Washability, useful in kitchens and bathrooms where the wall will be cleaned often.

To estimate the quantity, multiply the width by the height of each wall, subtract doors and windows, multiply by the number of coats and divide by the coverage rate. For a ceiling or a small bedroom, a small tin is often enough; there's no point buying a large tin "just in case" of a biocidal product that then sits in the storeroom for years.

How to paint with anti-mould paint: the right order

1. Lower humidity first. Measure for a week with a hygrometer at 7 am; the goal is 40–60%. Without this, nothing else lasts. See how to choose a hygrometer.
2. Clean off the mould. Diluted bleach, 1 part to 4 of water, with gloves, a mask and the window open. Never mix bleach with other products.
3. Rinse and let it dry as the label says — several days if the weather is damp. Painting a wet wall wastes paint.
4. Scrape off loose paint and treat cracks. New paint won't grip a peeling film.
5. Apply the paint in the coats and at the coverage rate stated on the spec sheet. A thin coat lasts less.
6. Keep up the routine: airing, extractor fan, laundry out of the bedroom. Paint doesn't make up for habits that generate vapour.

If the mouldy area is large, or you'd rather not handle the product, there are professional cleaning companies, with observed prices from €48 — see how much mould cleaning costs. Remember that cleaning, however good, doesn't treat the cause.

Thermal and "insulating" paints: what to expect

Some paints are sold as "thermal", "insulating" or "anti-condensation", some with ceramic or glass microspheres. The promise is usually to warm the wall surface enough to stop condensation and to save on heating.

Be sceptical. A paint film is a fraction of a millimetre thick; effective thermal insulation is measured in centimetres. Physics doesn't change with the product name. Some of these paints absorb and release a little vapour, which may delay droplets forming, but they're unlikely to raise the wall's temperature in any meaningful way.

Before buying, ask the seller for:

• the measured thermal conductivity (λ, in W/m·K), with the test standard stated;
• the dry film thickness that value corresponds to;
• whether the savings claim ("up to X%") comes from an independent test or from the manufacturer's own simulation;
• the full label, if the paint contains biocides.

If the spec sheet has no verifiable figures, treat the promise as advertising. For genuinely cold walls, the solutions with a measured effect are insulation, fixing thermal bridges around window frames and ventilation — a PIV system (VMI) in a flat costs ≈€800–2 500 (estimate).

How much to spend and what to avoid

For a bedroom with condensation already under control, the combination of hygrometer, cleaning, paint and small ventilation fixes usually fits within the €20–300 DIY range observed for condensation. Spending more on paint won't make up for an unresolved cause.

• painting over mould without cleaning — the fungi stay underneath and reappear through the film;
• painting the wall while it's still damp, right after washing it;
• using plastic or waterproof paints in old houses with lime plaster, which needs to let vapour out — see damp in old houses;
• accepting painting quotes for stains with salt deposits or water-ingress tide marks;
• choosing by an eye-catching label instead of the spec sheet.

We don't recommend paint brands: choose by the spec sheet, the coverage rate and compatibility with the surface. Some links on the site may be affiliate links and are always marked — see how we make money.