Every autumn the same calls start coming in. The heating goes on, the windows stay shut, and black spots appear in the corner of the bathroom ceiling, behind the wardrobe or around the bedroom window. The quickest fix seems obvious: grab a tin of white paint and cover it up. Unfortunately, painting over mould without treating it first is one of the most common decorating mistakes I see in Southampton homes – and it usually comes back within weeks.

Here is how I deal with mould properly before decorating, what paint actually works, and when the problem is bigger than a paint job.

Why You Can’t Just Paint Over Mould

Mould is a living growth, not a stain. It roots into the surface of plaster, filler and old emulsion. A fresh coat of standard emulsion does nothing to kill it – it simply gives the spores a new, slightly damp surface to grow through. Within a few weeks you get grey shadows, then black spotting, and often flaking or bubbling paint on top.

There is a second problem: mould tells you something is wrong with moisture in the room. If you only cover the symptom, you lose the warning sign while the cause carries on.

Step 1: Find Out Why the Mould Is There

Before anything is painted, it is worth working out where the moisture comes from. In most homes it is one of three things:

Condensation – by far the most common. Showers, cooking, drying clothes indoors and poor ventilation leave warm, wet air that settles on the coldest surfaces: ceilings, window reveals and external walls.
Penetrating damp – water getting in from outside through failed pointing, cracked render, blocked gutters or leaking window seals.
Rising damp or leaks – less common, but typically shows as tide marks low on walls, or damp patches under bathrooms and around pipework.

Condensation mould is usually spotty, spreads in corners and appears on cold walls. Penetrating damp tends to create a patch that grows after rain. If mould keeps returning in the same spot regardless of ventilation, or the plaster feels wet or crumbly, the building needs looking at before any decorating – a painter can’t fix a roof leak or a failed damp-proof course.

Step 2: Treat the Mould Properly

Once the cause is understood, the surface needs to be treated, not just wiped. My usual process looks like this:

Protect the room. Floors and furniture are covered and the area is ventilated. Mould spores are easily disturbed, so dry brushing or dry sanding is avoided.
Apply a fungicidal wash. A proper mould and algae treatment is applied generously and left to work for the time stated by the manufacturer. Household bleach can whiten the surface, but it does not reliably kill growth that has rooted into porous plaster.
Clean off the dead growth. The treated area is carefully wiped down and allowed to dry fully.
Repeat if needed. Heavy growth often needs a second application.
Remove failed paint and repair. Any flaking or blown areas are scraped back, filled and sanded – using dust-extracted sanding to keep the rest of the room clean.

Preparation is where most of the result is decided. You can read more about this stage in my guide to preparing walls for painting properly.

Step 3: Seal the Stains

Even after treatment, mould usually leaves grey or brown staining. Water-based emulsion won’t hide it – the marks bleed straight back through. A dedicated stain-block primer seals these areas so the topcoat stays clean and even. On ceilings affected by old leaks, this step is essential.

Step 4: Choose the Right Anti-Mould Paint

For bathrooms, kitchens, utility rooms and cold bedrooms, I recommend a paint designed for high-humidity areas. Good anti-mould paints contain a fungicide that protects the paint film itself, and they are usually more washable than standard matt emulsion, which matters in rooms that need regular wiping.

Be realistic about what it can do, though. Anti-mould paint resists growth on its surface for a number of years; it does not stop condensation forming. If a room is constantly running wet, mould will eventually find a way – on the grout, on the window seals, on the curtains. The paint is part of the solution, not all of it.

Sheen level also matters in wet rooms. If you are unsure what to use, my article on how to choose the right paint finish for every room explains the options.

Step 5: Stop It Coming Back

Southampton’s mild but wet coastal climate, combined with plenty of older terraced and semi-detached housing, makes condensation a very common issue here. A few simple habits make a big difference to how long a fresh finish lasts:

Run the extractor fan during showers and cooking, and for 15–20 minutes afterwards.
Open trickle vents on windows and keep them open during the colder months.
Avoid drying washing on radiators in poorly ventilated rooms.
Keep large furniture a few centimetres away from external walls to let air circulate.
Keep the heating at a steady, low level rather than short blasts – cold walls attract condensation.
Wipe condensation off windows and sills in the morning.

When to Call a Professional

A small patch of mould on a bathroom ceiling can be handled with the right products and patience. It is worth getting professional help when:

the mould covers a large area or several rooms,
it keeps coming back after you have treated and repainted,
paint is peeling, plaster is soft or there are signs of water getting in,
you are a landlord preparing a property for new tenants and need a durable, defensible finish.

For landlords in particular, a properly treated and sealed surface is far cheaper than repainting the same room every winter. My guide to repainting between tenancies covers this in more detail. The UK government has also published guidance on damp and mould for rented housing providers, which is worth reading if you let property.

Frequently Asked Questions

Can I paint over black mould with anti-mould paint?

Not directly. The mould needs to be killed and cleaned off with a fungicidal wash first, then any staining sealed. Anti-mould paint protects a clean surface – it is not designed to be applied over live growth.

How long does anti-mould paint last?

Most quality products protect the paint film for several years, but the real lifespan depends on ventilation. In a well-ventilated bathroom it can look good for many years; in a room with constant condensation, spotting can return much sooner.

Is it worth repainting in autumn or winter?

For interiors, yes. Indoor decorating can be done all year round, and treating mould early in the season stops it spreading through the winter. The key is allowing proper drying time between treatment, priming and painting.

Mould Treatment and Repainting in Southampton

If mould keeps coming back in your bathroom, kitchen or bedroom, I can assess the surface, treat it properly and repaint it with a finish suited to the room. As an NVQ Level 2 qualified decorator with over 15 years’ experience, I focus on the preparation that makes the result last – with full floor and furniture protection and a clean, tidy site throughout.

Find out more about my interior painting and preparation and repair work services, or get in touch for a free, no-obligation quote.

Painting Over Mould: How to Treat and Paint Damp Walls Properly