Can I just paint over a damp or mouldy wall?

Stains, bubbling and mouldMouldFungi that grow on damp surfaces, leaving black or greenish spots and a musty smell. It is a symptom of damp, not a problem with the paint. are not a paint problem. They are signs that water is getting into the wall or collecting on it. Paint over them without changing anything else and the water keeps working from inside, so sooner or later the new paint bubbles and falls off just like the old.

Damp has several causes, and each needs a different fix: moisture from the ground climbing up the base of the walls, water getting in from a roof, a balcony or an outside wall, a leaking pipe, or condensationCondensationMoisture in the air turning to water on cold surfaces such as windows, outside corners and ceilings. It is the most common cause of mould indoors., when the moisture in the air of the home turns to water on cold surfaces. Mould in corners, on ceilings and around windows usually points to condensation. Which cause applies in a particular home can only be judged on site.

In an old apartment, damp had blown the plasterRender (plaster)A layer of mortar (sand, cement or lime, and water) spread over brick or concrete to give a wall a straight, sound surface ready for paint or tiles. low on the walls and the paint was falling onto the floor. Everything loose was scraped off by hand down to a sound surface, the gaps were filled and then the wall was painted. In the same home, the ceiling around the water heater pipe had turned black with mould. It was cleaned off before painting, otherwise it would have come back through the new paint.

When the plaster has gone bad deeper down, the scraping does not stop at the paint. In another apartment, the wall behind the counter was stripped back to the masonry and plastered from scratch, so the new plaster sits on a sound base.

Keep in mind: cleaning, scraping and a good paint job fix the surface, not the cause. If the water is coming from the roof, a leak or the ground, that has to be dealt with first or at the same time, or the damage will return. With condensation, good ventilation and insulatingThermal insulationA layer of material that lets heat through only slowly, so a home keeps its warmth in winter and stays cool in summer. the cold surfaces help.