How To Get Rid Of Mould Before Painting A Bathroom

To get rid of mould before painting a bathroom, kill it first, then clean, dry, prime and paint. Spray the affected area with a proper mould killer and leave it for the time stated on the product. Wipe the dead growth away with a damp cloth, rinse, and let the surface dry completely. Seal any staining with a stain blocking primer and finish with a bathroom or anti-mould paint. Just as important, fix whatever is causing the mould, which in most bathrooms is condensation with nowhere to go.

Painting straight over mould does not work. The growth carries on underneath, the new paint lifts or discolours, and within a few months the black spots come back through. Government guidance on damp and mould is clear that simply removing surface mould will not stop it reappearing unless the underlying cause is tackled too.

Why bathrooms get mould in the first place

Bathroom mould is nearly always a moisture problem. A hot shower or bath fills the room with water vapour, and when that warm, damp air meets a cold surface it condenses. Ceilings above the shower, the corners of external walls, window reveals and the silicone around the bath stay damp for hours after each use, and mould spores settle and grow there.

From working with clients across Kent, we’ve found that the worst bathrooms are usually the ones with an extractor fan that is fitted but not doing its job. The fan is too small, the duct is blocked, or it switches off the moment the light does. In smaller terraced and semi detached homes, where the bathroom is often a converted box room with one cold external wall, mould almost always appears first in the top corner of that wall.

Leaks are the other cause. A failed seal around the bath, cracked grout or a weeping pipe can soak a wall from behind. That kind of damp looks different, often a brown tide mark with mould along its edge, and it needs the leak repairing before any decorating starts. Where tiles are involved, any damp behind them has to be sorted first, because sealing it in under new tiles or fresh paint only makes it worse.

Is it safe to remove bathroom mould yourself?

For small patches, yes, with sensible precautions. The government guidance recommends wearing a mask, gloves and goggles so you avoid contact with mould spores and cleaning products, and opening a window while you work. NHS inform notes that inhaling or touching mould spores can cause allergic reactions and that mould can trigger asthma attacks.

There are times to step back. NHS advice suggests calling in a specialist if the mould covers more than one square metre, or if it is caused by a problem with the building itself. Anyone whose asthma is triggered by mould should ask someone else to do the cleaning. Children, older people and anyone with a respiratory condition are at greater risk from mould exposure, so keep them out of the room while you work.

Step by step, how to get rid of mould before painting

1. Kill the mould with a dedicated product

Use a mould killer made for walls and ceilings rather than household bleach. The government guidance says mould and mildew products should be used in preference to bleach for health and safety reasons. Follow the label closely. Ronseal’s 3 in 1 Mould Killer, for example, is sprayed on until the surface is thoroughly wet, left for five minutes, then wiped away with a damp cloth or sponge. Other brands use different contact times, so check yours.

In our experience, a dedicated mould killer works better than bleach because it is designed to treat the growth on painted plaster and leave a surface that can be decorated, while bleach mainly lightens the colour of the staining and adds moisture to a wall that is already damp. When the black marks fade, it is easy to assume the job is done, when the mould is very often still active underneath.

2. Remove the dead growth and clean the surface

Once the treatment has worked, wipe away the residue with a damp cloth and rinse with clean water. Avoid dry brushing or sanding live mould, because it pushes spores into the air. If the old paint is flaking where the mould sat, scrape it back only after the area has been treated, and wear a mask while you do it.

Bathroom walls also carry a film of soap, hairspray and body products that paint will not stick to. A wash with sugar soap or a degreasing cleaner, followed by a rinse, gives the new coating a clean surface to bond to.

3. Check and replace the silicone

Mould growing inside the silicone around a bath or shower tray cannot be cleaned out, because it has grown into the sealant itself. The only fix is to cut the old silicone out, clean and treat the joint, let it dry and run a new bead of sanitary sealant. Do this before painting so the finished room looks fresh from top to bottom.

4. Let everything dry properly

This is the stage most people rush. A treated wall can feel dry to the touch while the plaster behind it is still holding moisture, and paint applied too soon will struggle to bond. Run the extractor fan, keep the door open, avoid using the shower if you can, and give the room at least a full day. In winter, or in a bathroom without a window, allow longer.

5. Prime any stains

Mould often leaves a grey or brown shadow behind, even after it has been killed. Ordinary emulsion will not hide it for long. A stain blocking primer seals the mark so it cannot bleed through the topcoat. Zinsser’s guide to painting over mould follows the same order of treat, prime with a stain blocker, then finish with an anti-mould paint. Zinsser primers are among the products we rely on for problem surfaces, and a stained bathroom ceiling is exactly the kind of surface they are made for.

6. Paint with a bathroom or anti-mould finish

Choose a paint made for high moisture rooms. Bathroom paints are designed to resist condensation and wipe clean, and many contain a fungicide that slows regrowth on the paint film. Apply two full coats and leave the room ventilated while they dry. Fungicidal paint is a backup, not a cure. If the moisture is still there, mould will eventually find a way back.

Fix the cause or the mould will return

Every guide to getting rid of mould ends in the same place, which is ventilation. Building Regulations guidance in Approved Document F sets a minimum rate of 15 litres per second for an intermittent bathroom extractor fan in new or altered work. In a room with no openable window, the fan should keep running for at least 15 minutes after the room is left.

Older bathroom fans often fall short of that, especially if the duct is long, kinked or clogged with dust. If the mirror is still steamed up long after a shower, the fan is not clearing the room. A fan on a timer or humidity sensor, a slightly open window after showering and wiping water off the tiles all help.

We’ve found that the order matters more than the product. A bathroom that is treated, dried and repainted with the ventilation sorted at the same time holds up. One that is repainted while the moisture problem remains is simply being redecorated for the mould to grow back on.

What we see on Kent bathrooms

With more than 30 years of decorating across Kent and more than 200 residential projects behind us, a few patterns repeat. Many Victorian and Edwardian terraces in Medway and Maidstone have solid walls with no cavity, and a cold external wall is exactly where bathroom condensation settles. On these properties we take extra care with the choice of finish, because some modern coatings trap moisture in an older wall and push it back out as blistered paint.

In newer homes the problem is usually different. Bathrooms in many new builds have no window at all, so the extractor fan is the only route out for moisture. If the fan’s overrun timer has been switched off or the filter is clogged, mould appears surprisingly quickly, often on the ceiling directly above the shower.

Quick checklist before you pick up a roller

• Find and fix any leak or failed seal first.
• Wear gloves, goggles and a mask, and open a window.
• Treat with a dedicated mould killer and follow the stated contact time.
• Wipe, rinse and clean off soap and grease.
• Replace mouldy silicone.
• Let the room dry for at least a day.
• Spot prime stains with a stain blocking primer.
• Apply two coats of a bathroom or anti-mould paint.
• Check the extractor fan works and use it every time.

Conclusion

Getting rid of mould before painting a bathroom comes down to doing the stages in order. Kill the mould, clean the surface, let it dry, block any staining and finish with a paint made for wet rooms. Then deal with the moisture that caused it, or the best paint job in the world will not last.

If your bathroom keeps growing mould no matter how often you clean it, A-Z Decorators can treat it, prepare it and repaint it properly as part of our interior decorating across Kent. Contact us for a free quotation and honest advice on what your bathroom needs.