Guide
How to remove black mould, and why bleach is not the answer
Clean small patches on hard surfaces with a mould and mildew spray, wearing gloves, goggles and a mask, with the window open and the door shut. Bleach lightens mould on porous surfaces without removing it, and mould that keeps returning needs its cause fixed.
First, is this a job for you?
The government's guidance on damp and mould says most tenants could reasonably be expected to remove condensation and very small amounts of mould with an appropriate mould and mildew cleaner, and that larger areas should be dealt with by professionals.
In practice, leave it to somebody else if the mould covers a large part of a wall or ceiling, keeps coming back within weeks of cleaning, is on plaster that feels soft or crumbly, or has followed a leak or a flood. The same goes if anyone in the house is pregnant, has asthma or another lung condition, or has a weakened immune system: they should not be the one doing the cleaning, and ideally should be out of the room while it happens.
What you need
- a mould and mildew spray, used according to its label
- rubber gloves and goggles
- a mask, so you are not breathing what you disturb
- disposable cloths or kitchen roll, and a bin bag to seal them in
- a bucket of clean water and a separate cloth for rinsing
- old clothes that can go straight in the wash afterwards
How to do it
- Ventilate one way. Open the window and close the door, so spores go outside rather than into the rest of the house.
- Clear the area. Move clothes, bedding and anything soft away from the patch.
- Spray and wait. Apply the product and leave it for the time on the label. Do not brush or scrape mould dry first, because that sends spores into the air.
- Wipe, do not scrub hard. Lift the growth off with a disposable cloth, turning it often, and bag each cloth as you finish with it.
- Rinse and dry. Wipe over with clean water, then dry the surface fully with the heating on and the window open.
- Clear up. Seal the bag, wash the clothes you wore, and keep the room ventilated for a few hours afterwards.
Does bleach kill mould?
The government guidance says mould and mildew products should be used in preference to bleach, for health and safety reasons. Bleach also works less well than people expect. On glass, tiles and other hard, non-porous surfaces it can remove mould, but on plaster, paint, grout, wood and silicone it bleaches the visible growth white and leaves the rest in the material, which is why the patch looks cured and then comes back darker.
Never mix bleach with another cleaning product. Bleach with an acid cleaner such as a descaler or some toilet cleaners gives off chlorine gas, and bleach with ammonia gives off chloramine. Both are harmful to breathe in a small bathroom.
Surface by surface
| Where it is | What to do |
|---|---|
| Window frames and glass | Spray and wipe. Wipe condensation off each morning and it rarely returns |
| Silicone sealant | Surface spots clean off. Black inside the silicone means cutting it out and resealing |
| Grout | Mould spray and a stiff brush, then rinse. Stained grout can be recoloured |
| Painted walls and ceilings | Clean, dry, fix the cause, then repaint with a mould-resistant paint |
| Wallpaper | Usually has to come off, because the growth is behind it as well |
| Carpet, mattresses, sofas | Often impossible to clean fully, and may have to be thrown away |
| Clothes and curtains | Wash as hot as the care label allows, and dry them outside if you can |
Why it keeps coming back
Mould returns because the conditions that grew it have not changed. Condensation is the most common cause: a household puts a lot of water into the air through cooking, bathing, drying clothes and breathing, and it condenses on the coldest surfaces. That is why mould turns up on outside walls, in corners, behind wardrobes and on bedroom walls after a night with the door and window shut.
The fixes are unglamorous and they work: lids on pans, extractor fans on while cooking and showering and for a while after, a window open a crack when drying washing indoors, heating kept at a steady moderate level rather than off and on, and a gap between furniture and outside walls. A dehumidifier helps in a room that stays damp.
Mould in one defined patch that grows after rain is different. That is water getting in from outside or from a leak, and no amount of cleaning or ventilating will fix it. A tidemark low on a ground floor wall can be rising damp, although the government guidance notes that rising damp is often misdiagnosed.
When to call in a specialist
A specialist treatment costs about £120 to £300 for a single wall or bathroom area and £200 to £600 for a whole room, and a damp survey is £150 to £400 where nobody is sure what the cause is. Fitting or upgrading an extractor fan is often the cheapest lasting part of the answer.
If you rent, report the mould to your landlord in writing before paying anyone. The underlying cause is normally the landlord's responsibility, and in social housing in England there are now fixed deadlines for dealing with it.
Common questions
Why is there mould on my bathroom ceiling?
Warm, wet air rises and condenses on the coldest surface, which in a bathroom is often the ceiling under a cold loft or an outside corner. Run the extractor during the shower and for twenty minutes after, and check it is pulling air: a sheet of toilet paper held to the grille should stay there.
Is anti-mould paint worth using?
Only after the mould has been cleaned off, the wall has dried and the moisture source has been dealt with. It slows regrowth on a dry wall. On a damp one it is a short delay.
Can I clean mould while pregnant?
Better if somebody else does it. Pregnant women are among the groups the government's damp and mould guidance names as most at risk, along with young children and anyone with a lung condition.
Why do I keep getting mould in my bedroom?
Two adults breathe a surprising amount of moisture into a closed room overnight, and a bedroom is often the coldest room in the house. Open the window for a while each morning, keep the room gently heated, and pull wardrobes and beds away from outside walls.