Mould on the bathroom ceiling: how to fix it

Mould on the bathroom ceiling appears because the vapour from showers rises and condenses on a cold surface. To fix it, clean the mould wearing gloves and a mask, dry thoroughly, paint with a suitable paint and, above all, improve the ventilation.

Why it appears on the ceiling

Hot, humid air rises. It reaches the ceiling, which is usually the coldest part of the room, and turns into droplets. If this repeats every day and the ceiling is slow to dry, mould grows.

Bathrooms with no window, with a weak fan or with poorly connected ventilation often have this problem. In buildings where the bathroom is on the top floor, the ceiling can be even colder, because it is more exposed.

First check it is not a leak

Not every stain on the ceiling is condensation. Suspect a leak if:

• the stain is yellowish or brownish and has defined edges;
• the ceiling is wet even when nobody has had a shower;
• the paint is blistering or the plaster is falling;
• the stain grows after it rains, if there is a terrace or roof above;
• the bathroom is under another bathroom or a kitchen.

In these cases, call a plumber or speak to the neighbour upstairs before painting.

How to clean mould off the ceiling

1. Open the window, if there is one, and protect yourself with gloves, a mask and safety goggles.
2. Cover the floor and the sanitaryware with plastic sheeting or cloths.
3. Dampen the area with a damp cloth. That way less dust is released.
4. Scrub with warm water and washing-up liquid, or with a product made for mould, following the packaging.
5. Wipe with a clean damp cloth and dry well.
6. Throw the cloths away in a sealed bag.

Do not mix cleaning products, especially bleach with other products. It can release dangerous gases.

How to paint the ceiling

Wait until the ceiling is completely dry. This can take a few days.

1. Scrape off loose paint and lightly sand rough areas.
2. Repair holes and cracks with a suitable filler.
3. Apply a primer suited to damp areas.
4. Paint with a paint made for bathrooms and kitchens, one that is washable and damp-resistant.
5. Apply two coats, with the bathroom well ventilated.

Tip: Painting the ceiling from top to bottom with a short-pile roller gives a more even finish. Always use a stable ladder.

How to stop it coming back

• If you have a window, open it during the shower and for about fifteen minutes afterwards.
• If you have no window, use an extractor fan and check that it works. A thin piece of paper held against the grille should stay stuck there when the fan is on.
• Leave the fan running a while longer after the shower.
• Keep the door closed during the shower, so the vapour does not spread to the rest of the home, and open it afterwards.
• Clean the fan grille regularly, because dust reduces extraction.
• Avoid drying laundry in the bathroom.
• Wipe the tiles and glass with a cloth or squeegee to remove the water.

When to ask for help

If the mould comes back a few months later, if the ceiling is deteriorating or if the stain is large, ask a professional to assess it. There may be a ventilation problem, an insulation problem or a leak.

In homes near the sea, in Cascais or Oeiras, or in the Sintra area, the air already carries more moisture. Bathroom ventilation is even more important.

See also

• Why paint bubbles and peels
• Anti-mould and anti-condensation paint: what they do
• Dehumidifiers: do they really help with damp?
• What is efflorescence (salt deposits) and how to treat it