Damp
Black mould in bathrooms and bedrooms: why it appears and how to treat it
Those black spots that appear on the bathroom ceiling, in the corners of the bedroom or behind the wardrobe nearly always have the same cause: condensation. Painting over them hides them for a few weeks, but they come back. Here we explain why they appear and how to treat them properly.
What that black mould is and why it appears
Mould needs moisture to grow. In bathrooms and bedrooms that moisture does not usually come from outside, but from inside the home itself: steam from the shower, our breathing while we sleep, washing dried indoors or cooking.
When that moisture-laden air touches a cold surface, the water condenses, just like on a glass with ice in it. If the wall stays damp for hours, the black spots appear. That is why they show up mainly on:
- Ceilings and corners of bathrooms with no window or with poor ventilation.
- Bedroom corners and walls facing the outside.
- Behind wardrobes and furniture pushed up against the wall, where the air does not circulate.
Why it happens so often in coastal homes
On the coast the air is more humid, and many homes stay closed up for weeks or months out of season. A closed-up home is not ventilated, the moisture builds up and the mould finds perfect conditions.
It is very common to arrive at the beach house after the winter and find the bathroom ceiling or the bedroom corners covered in black stains, even though there is no leak at all.
How to tell condensation from a leak
Not all damp is condensation, and the difference matters, because the treatment is different:
- Condensation: scattered black spots, in cold, poorly ventilated areas, which get worse in winter or when the home is closed up.
- Leak: stains that appear or grow after it rains, with yellowish rings, on ceilings below terraces or on outside walls.
If it is a leak, the water getting in has to be stopped first. We explain it in damp stains on walls and ceilings.
How it is treated before painting
Painting over mould does not get rid of it: it covers it, and it comes back through the new paint. The right treatment has three steps:
- Clean and treat the mould with an anti-mould product, letting it work and letting the wall dry properly.
- Make good the areas where the old paint has deteriorated.
- Paint with a paint designed for damp, made for bathrooms, kitchens and areas with condensation.
It is the work we do in interior painting when there is damp.
What you can do to stop it coming back
The right paint helps a lot, but condensation is fought above all with ventilation:
- Open the window or switch on the extractor fan after a shower.
- Air the bedrooms for a while every morning.
- Move wardrobes slightly away from walls that face the outside.
- If the home is going to be closed up for a long time, have someone air it from time to time.
How we do it
We come and see the home at no cost, tell you whether the stains are condensation or a leak, and give you a fixed quote in writing to treat them and paint. If it is not a painting job, we tell you, so you do not waste money.
Frequently asked questions
Why is black mould appearing on my bathroom ceiling?
Nearly always because of condensation: steam from the shower condenses on the cold ceiling and, if the bathroom is not ventilated, the moisture stays and mould appears.
Is it enough to paint over the mould?
No. It has to be cleaned and treated first, and painted with a paint designed for damp. If it is only painted over, it comes back.
Does anti-damp paint solve it for good?
It helps a lot, but if the home is not ventilated, the condensation will carry on. Paint and ventilation go together.
Will you come and see whether it is condensation or a leak?
Yes. The visit is free and we tell you what it is and what is best to do.
