Mould in bathrooms: why it keeps coming back after painting
2 August 2026 · 4 min read
Painting over mould does not kill it, and anti-mould paint is not a cure. What actually stops it returning, and the one thing most bathrooms are missing.
Mould on a bathroom ceiling is the single most common interior problem we are called about, and the single most commonly mis-fixed.
The reason it comes back is almost always the same: the mould was painted over rather than removed, and nothing changed about the conditions that grew it.
What mould actually needs
Three things, and you only have to remove one:
- **Moisture** — condensation on a cool surface
- **A food source** — dust, soap residue, and the surfactants in some paints
- **Still air** — nothing to carry the moisture away
Bathrooms provide all three by design. A hot shower puts a remarkable amount of water into the air, and a ceiling is the coolest surface in the room, so that is where it condenses.
Why painting over it fails
Mould is a living organism with a root structure that penetrates the coating and, in some cases, the plasterboard behind it. Rolling paint over it does three things:
- Hides it for a few weeks
- Gives it a fresh food source in the new film
- Seals moisture into the substrate underneath
It will be back, and it will usually be worse, because it is now growing under a layer that is holding moisture against it.
Bleach is not the answer either
Household bleach removes the colour from mould without reliably killing it — the surface looks clean while the organism is intact. The stain disappears, you paint, and it returns through the new coating. Use a proper fungicidal wash, not chlorine bleach.