Mould on a bathroom ceiling is the job people apologise for before I’ve got my coat off. They shouldn’t. In a converted flat off Salusbury Road in Queen’s Park — one sash painted shut, an extractor that gave up years ago — black spotting across the ceiling is close to inevitable. It’s physics, not neglect.
I get called to these constantly. Top-floor conversions and basement flats. The little internal bathrooms with no window at all that developers love to carve out of a box room. Same story every time. Somebody wipes the ceiling, it looks clean for a fortnight, the black comes back darker.
This is how I shift it properly. The harder part is stopping it coming back.
Why does mould keep coming back on a bathroom ceiling in a badly ventilated flat?
Warm wet air rises. You run a hot shower, the room fills with steam, and that steam goes straight up and hits the coldest surface in the room — the ceiling, especially the bit nearest an outside wall or under a cold roof void. It condenses there into a film of water. Do that twice a day, every day, with nowhere for the moist air to escape, and you’ve grown mould whether you like it or not. The spores are already in the air. All they need is damp and something to feed on, and emulsion paint feeds them nicely.
Warm air, a cold ceiling, and nowhere for the wet to escape — that’s the whole recipe.
The ventilation is the game. A working extractor pulls the wet air out before it can settle. In half the flats I visit the fan spins but moves nothing — the ducting’s blocked, or it vents into the loft instead of outside. The corners and the wall above the shower go first, because they stay coldest and wettest. That’s where you’ll see it start, a fine grey speckling before it turns to proper black blotches. Same story in every damp bathroom I walk into.
What’s the difference between mould and a bit of surface mildew?
Worth knowing before you scrub. Mildew is the flat, grey-to-white powdery film — surface-level and slow to return, wipes off with a cloth. Mould is the raised black or dark-green spotting that’s got its roots into the paint film and sometimes the plaster behind. On a long-neglected ceiling it can go deep enough that cleaning the surface only buys you weeks.
If you wipe it and a brown or black shadow stays in the paint after it’s dry, the growth is into the substrate, and no amount of scrubbing brings that back. That ceiling needs stripping and repainting, not cleaning.
Is it safe to clean it yourself, and when should you stop?
For a patch the size of a dinner plate, on a sound ceiling, in a flat with a window you can open — clean it yourself and don’t lose sleep. Open the window wide and wear a mask, and you’ll be fine.
There’s a point where I’d stop, though, and tell a client to get someone else in. If the affected area is bigger than about a square metre, or if anyone in the flat has asthma or a chest condition, disturbing that much mould pushes a lot of spores into the air of a small room. That’s when it stops being a wipe-down and becomes a job for someone with proper extraction and containment. I say so, even when it means turning work away.
The problem with reaching for bleach
Everyone reaches for bleach. I’d rather they didn’t. Household bleach on a ceiling does one thing well — it takes the colour out of the mould, so the black vanishes and the ceiling photographs beautifully for the letting agent. Underneath, the growth is often still alive, and within a month it’s back through the paint. Estate agents love bleach for exactly this reason. It looks solved.
Bleach is also mostly water, and you’re adding more moisture to a ceiling that already has a moisture problem. On a painted surface it beads and runs and never reaches the paint film where the roots sit. A proper fungicidal wash — the kind sold for this exact job — kills the growth and leaves a residue that slows regrowth, and it doesn’t dump a pint of water on the plaster doing it. I use bleach for almost nothing on ceilings now.
How do you get mould off a painted bathroom ceiling properly?
Ventilate first. Open every window in the flat and shut the bathroom door, so you’re not seeding spores through the rest of the place. Put a mask on — a proper FFP2, not a dust hankie. Mould you disturb goes airborne, and you don’t want a lungful of it in a room that size.
Don’t dry-brush it. Scrubbing dry mould is the single worst thing you can do, because it flings spores everywhere and seeds the rest of the ceiling. Wet it down first. Mist the area with your fungicidal wash — or a dilute solution if you’re working from a concentrate — and let it sit. Ten minutes, longer on stubborn black. The point is to kill and soften the growth so it lifts rather than dusts off.
Then wipe, don’t scrub. A damp cloth or a soft sponge, one direction, folding to a clean face as you go and binning the cloth after — don’t wring a mould-loaded cloth back into your bucket and paint it around the room. Work in small sections. The black should lift onto the cloth. Where it’s ground in, a second application and a longer soak beats elbow grease every time.
Once it’s off, wash the area again with clean fungicidal solution and leave it to dry without rinsing — that residue is what holds the next lot back. Get some air moving. If there’s any working ventilation at all, run it for a few hours after.
One thing people skip: the sealant where the wall meets the ceiling, and the top run of tiles. Mould loves silicone sealant and it’ll sit in there and reinfect the ceiling from below. If the sealant’s gone black through, cleaning won’t save it — it wants cutting out and replacing.
Dealing with a textured or Artex ceiling
The rough ones are a trap. A lot of these conversions have a swirled or stippled ceiling, and pre-2000 Artex can contain asbestos. You don’t sand it and you don’t scrape it. Nothing abrasive, full stop. If the ceiling’s textured and you don’t know its age, treat it as though it does contain asbestos — gentle wet wiping only, and if the mould’s grown into the texture rather than sitting on top, get it tested before anyone goes near it with a tool.
How do you stop it coming straight back?
Cleaning is the easy half. If the flat still fills with steam twice a day and the wet air has nowhere to go, you’ll be back up that ladder by spring. I’ve re-cleaned the same ceiling for the same tenant three times in a year before we worked out the fan was wired to the light in the hall and never once came on. The extractor is the first thing to sort. After that it’s habits, and if it’s still coming, the building itself.
Run the fan every time and leave it running. Most bathroom extractors have an overrun timer; if yours doesn’t, leave it on fifteen minutes after you’ve finished. Open the window while you shower if you’ve got one that opens. Squeegee the tiles and wipe the worst of the water off afterwards — less standing water means less to evaporate back into the room.
Keep the bathroom door shut during and after a shower, so the steam doesn’t roll into colder rooms and condense on their walls instead. If you dry washing on a radiator in a small flat, that water goes somewhere too. Usually the bathroom ceiling.
The extractor fan nobody ever cleans
Pop the cover off your extractor and look at it. In most flats I visit it’s furred with a grey felt of dust that’s choking the airflow to nothing — the motor runs and the blades turn, but barely any air moves. Even a healthy fan can’t cope like that. The cover usually unclips; wash it in warm soapy water and brush the dust off the blades gently. Then check the flap on the outside wall isn’t painted shut or bunged with an old nest. That five-minute job restores more ventilation than most of what people spend money on.
If the fan vents into the loft rather than through the wall — and a shocking number do — you’re pumping wet air into the roof space and it comes straight back through the ceiling. Furred cover, ducting to nowhere. Same story in half the conversions round Kilburn. That one’s for a builder, not a cloth.
When is it not a cleaning job at all?
Sometimes the mould is a symptom of something a cleaner can’t touch, and pretending otherwise wastes the client’s money. If the same patch keeps returning in exactly the same spot within weeks of a proper clean, the problem’s in the building, and no product I own will hold it back for long.
The split that matters is condensation versus a leak, and they need different people.
Condensation or a genuine leak?
Condensation mould spreads over a broad area — the whole ceiling and the wall over the shower — following wherever the warm wet air settles. It’s diffuse and it tracks the cold spots. A leak looks different. A defined patch, often browner or ringed with a tide-mark, sometimes soft or sagging, sitting in one specific place that doesn’t match where the steam goes. A patch right under a flat roof or a soil pipe that’s wet to the touch when nobody’s showered is a leak, and it wants a roofer or a plumber before anyone bothers cleaning it.
I’ll tell a client which of the two I think it is, then get out of the way of the right trade. Cleaning a leak is painting over a warning light.