Mould, damp stain and water damage painting

Why painting over mould does not work on its own

Painting over mould with ordinary emulsion hides it for a few weeks at most. The spores are still alive under the new paint and the conditions that caused them, usually condensation, have not changed, so the black spots grow back through, often worse than before. Water and smoke stains behave in a similar way: they contain salts and tars that bleed through water-based paint.

A lasting result needs three things: dealing with the cause, treating the surface properly, and using paints designed for the conditions.

Fix the cause first

Most mould in homes comes from condensation, when warm, moist air from cooking, showers and drying clothes meets a cold wall, ceiling or window reveal. It appears in the corners of external walls, behind wardrobes and on bathroom ceilings. Better ventilation, such as working extractor fans, open trickle vents, lids on pans and windows opened after showers, makes more difference than any paint.

Some problems are not condensation at all. A patch that grows after rain, a stain below a bathroom, or damp creeping up from the floor points to a leak, a roof or gutter fault, or rising or penetrating damp. Those need a plumber, roofer or damp surveyor before redecoration, and we will say so if what we see looks like one of them rather than paint over it.

How mould is treated before painting

1. The affected area is treated with a fungicidal wash and left for the recommended contact time, so the spores are killed rather than just wiped around.
2. Dead growth is removed with a damp cloth or scrubbing, never dry-brushed into the air.
3. The surface is rinsed if the product requires it and left to dry thoroughly.
4. A stain-block primer goes over any marks the mould has left.
5. Two coats of an anti-mould or anti-condensation emulsion finish the surface.

As an example, mould treatment with stain block in one room typically comes to £100–£200.

Nicotine, smoke and other stains

Nicotine and smoke leave a yellow-brown film across walls and ceilings, often most obvious when pictures come down. It is washed off with sugar soap first, then sealed with a stain-block primer, often a solvent-based or shellac-based one for heavy staining, before any emulsion. The same approach works for marker pen, crayon, rust marks and tannin bleeding through from timber. It is a common part of preparing a property between lets; the landlord repainting page covers that work.

Repainting after a leak or water damage

Once the leak has been repaired, the ceiling or wall has to dry out completely. Soaked plaster can take several weeks to dry, longer in winter, and painting too soon traps moisture so the stain returns as a tide mark. A moisture meter reading helps decide when it is ready.

If plaster has blown, cracked or sagged, or a plasterboard ceiling has gone soft, those sections need re-plastering or replacing first, and the new plaster then takes a mist coat before finishing. If the damage is part of an insurance claim, keep photos of the damage before and during the work, and ask for the quote in writing so it can go with your claim. The ceiling painting page covers repainting a whole ceiling once repairs are done.

Anti-mould and anti-condensation paints

Anti-mould emulsions contain a fungicide that resists regrowth on the paint film. Anti-condensation paints add a slightly insulating layer that slows the formation of moisture on cold surfaces. Both help in bathrooms, kitchens and cold bedrooms, including those in Victorian terraces in Ealing with solid external walls, but neither can overcome a room that is never ventilated.

To price the work, the Instant Quote lets you describe the problem and upload photos of the affected area. A decorator reviews them, and may suggest a short video call if the cause is unclear.