How to Get Rid of Black Mould in Bathrooms
How to safely remove black mould from bathroom walls, grout and sealant, why it keeps coming back and when it signals a bigger damp problem.
Black mould in bathrooms is common in UK homes because warm, damp air meets cold surfaces. Small patches can be cleaned safely at home, but the key to keeping it away is dealing with moisture, not just scrubbing. This guide covers cleaning methods and prevention. It is general information, not professional advice.
First, assess the problem
Small spots on grout, sealant, ceilings and corners are usually surface mould caused by condensation. Large areas, mould that returns quickly, a musty smell with no visible source, or mould associated with leaks and damp patches may indicate a deeper issue such as a leak, penetrating or rising damp. In those cases, cleaning will not solve it, and you should have a qualified professional look at the cause. Tenants should report it to the landlord in writing.
Protect yourself
- Wear rubber gloves, eye protection and a mask or respirator if there is a lot of mould.
- Open windows and doors, and use the extractor fan.
- Do not brush dry mould, which releases spores.
- Keep children, and anyone with asthma or respiratory conditions, away from the area.
- Never mix bleach with other cleaning products.
Cleaning methods
On grout and tiles
- Spray with a mould remover, or a mix of white vinegar and water, and leave for 10 to 15 minutes.
- Scrub with a stiff brush or old toothbrush.
- Rinse with clean water and dry thoroughly.
- Repeat if necessary.
Bicarbonate of soda paste can help with stubborn grout. Many shop-bought mould sprays contain bleach or similar; follow the label carefully.
On silicone sealant
Mould often grows into the sealant itself. If it stays black after cleaning, the sealant needs to be removed and replaced:
- Cut out old silicone with a sealant remover or sharp knife.
- Clean and dry the surface completely.
- Apply a bathroom-grade anti-mould sealant and smooth it.
- Allow it to cure as directed before using the shower.
On painted walls and ceilings
Wipe with a mould cleaner or diluted detergent, then let dry. Repaint with an anti-mould or bathroom paint once the surface is completely dry. Remember that porous surfaces like plaster may hold stains even after the mould is gone.
On shower curtains and fabrics
Wash according to the label, or replace if heavily affected.
Why it comes back
Mould thrives on moisture and poor ventilation. To stop it returning:
- Run the extractor fan during and for 15 to 20 minutes after showers. Check it is actually working.
- Open a window if you have no fan.
- Wipe down tiles, glass and sills with a squeegee or cloth after use.
- Keep doors closed during showers, so steam does not spread to cold bedrooms.
- Dry towels outside the bathroom, or on a heated rail, and avoid drying laundry in the bathroom.
- Heat the room modestly to keep surfaces from becoming very cold.
- Fix leaks promptly.
Professional help
If mould covers large areas, returns repeatedly, or is linked to leaks, a damp specialist or builder should diagnose the cause. For a thorough bathroom clean, including grout, limescale and sealant checks, a professional cleaner can help; see deep clean costs. For limescale specifically, see our deep cleaning checklist.
Which method for which surface
| Surface | Suggested approach | Avoid |
|---|---|---|
| Tiles and grout | Mould remover or vinegar solution, brush, rinse | Wire brushes that scratch |
| Silicone sealant | Clean; replace if stained throughout | Painting or covering over |
| Painted ceiling | Mould cleaner, dry, anti-mould paint | Soaking plasterboard |
| Wooden window frames | Gentle cleaner, dry, treat per paint type | Heavy scrubbing |
| Shower curtain | Machine wash or replace | Leaving it bunched |
Worked example: a shower corner
You notice black spotting along the bottom sealant and the corner grout. Open the window and run the fan. Spray the area, leave for the time on the label, scrub gently, rinse and dry with a cloth. If the sealant stays dark underneath, cut it out, let the area dry for a day, and reseal. Then wipe the screen after every shower for the next few weeks. If the spots return within a month, the real issue is ventilation or a hidden damp source.
Common mistakes
- Scrubbing dry mould and breathing in the spores.
- Using stronger and stronger bleach instead of fixing ventilation.
- Painting over a damp patch, which hides but does not cure it.
- Keeping the bathroom door open during showers.
- Ignoring a weak extractor fan that barely moves air.
Rentals and flats
If you rent, send photos and a short written note to your landlord or agent, and keep a copy. In flats with internal bathrooms and a shared ventilation duct, a weak fan may be a building issue rather than something you can fix. Tell the managing agent. Meanwhile, wipe surfaces, open windows when possible and keep belongings away from affected walls.
When it is not just cleaning
Repeated mould on external walls, a musty smell in rooms away from the bathroom, bubbling paint or wallpaper, or damp patches that grow after rain suggest a building problem. Ask a qualified surveyor or damp specialist to find the cause, and be wary of treatments offered without a clear diagnosis.
Frequently asked questions
Is black mould dangerous?
Mould can irritate the airways and trigger symptoms in people with asthma or allergies. If anyone in the household is affected, ventilate, clean carefully and seek medical advice for health concerns.
Does bleach kill mould?
Bleach can whiten surface mould on non-porous surfaces, but it does not always deal with the underlying growth in porous materials. Fixing moisture is more important.
Can I paint over mould?
Not before cleaning and drying. Painting over mould without treatment usually fails. Use an anti-mould paint on a clean, dry surface.
How long should I leave the mould cleaner on?
Follow the product label. Typically 10 to 15 minutes for sprays, but some need longer. Do not let it dry on the surface, and always rinse and ventilate.