Can you paint over mould?

It is tempting. The stain is ugly, a tin of paint is cheap, and one afternoon makes the wall look new. The trouble starts a few weeks later.

What happens when you paint over mould

• The mould is still alive. Ordinary emulsion has nothing in it that kills mould. The growth carries on underneath.
• The paint becomes food. Mould feeds on the binders in paint, so a fresh coat gives it more to eat.
• Moisture gets trapped. A new paint film slows the wall drying out, which is the opposite of what the wall needs.
• It comes back through. First as grey shadows, then as spots, and the paint may blister or peel.

Does anti-mould paint work?

Anti-mould paint contains a fungicide that slows new growth on the paint surface. It is useful as the last step on a wall that is clean and dry. It does not work as a cover for existing mould, and it does not last if the room is still damp. Most products are clear about this on the tin.

The right order

1. Find the moisture. Condensation, a weak bathroom fan or a leak. See why mould keeps coming back.
2. Remove the mould. Clean off the growth and treat the surface so what has grown into the plaster is dealt with too.
3. Let the wall dry. This can take days to weeks, depending on how wet it was.
4. Fix the cause. In most homes that means better ventilation.
5. Prime and paint. A stain-blocking primer first, then anti-mould paint in bathrooms and other damp rooms.

What about a small patch?

A patch smaller than a dinner plate on a painted bathroom ceiling can usually be cleaned, dried and repainted by a careful homeowner. Wear gloves and a mask, keep the window open and do not dry-brush the mould, because that spreads spores.

When to call a professional

• The mould covers more than about one square metre
• It has come back after cleaning or painting before
• It is on several walls or in several rooms
• Someone in the home has asthma, allergies or a weakened immune system
• The wall feels damp or the plaster is crumbling

In those cases painting is the last five percent of the job. Our free survey tells you what the first ninety-five percent needs to be: mould removal in Dublin.