Dealing with black mould in a bathroom is something I’m often asked to do in my role as a Professional Decorator, particularly when working for landlords, but it can occur in almost any home.
People see black mould and panic, which they should in a way because it can be harmful. However, it is relatively easy to treat once you understand it. Mould is a fungus, which means it’s alive. It will grow anywhere that conditions permit.
In this blog, I’m going to take you through some of the factors that can lead to black mould growth in your bathroom, and give you the solutions. I’ll then explain how to treat the mould and paint over it in a way that prevents it from returning.
The information on this blog will help you diagnose the issue and fix it.
What Causes Black mould in a Bathroom
Black mould grows in warm humid conditions, which is why bathrooms and shower rooms are hotspots. It’s likely to take hold on any surface that stays wet for prolonged periods.
Lack of Ventilation
You can’t prevent steam from condensing in a bathroom, but an extractor fan or open window will allow some of that steam to escape straight away, and it’ll help dry surfaces after using the bath or shower.
I work in a lot of rental properties, and I often see black mould in bathrooms where the tenant has turned the extractor fan off. So, if your bathroom suffers with mould, then the first thing you should do is check you have a working extractor fan.
Cold Walls
Water vapour condenses on the coldest surface. So, if you have an exterior wall with poor insulation, then it will stay wetter for longer than the other surfaces in your bathroom. This gives black mould more of a chance to take hold.
There are anti-condensation paints on the market you can look at for this. Or you could have a builder check the wall cavity. In extreme cases you can retrofit insulation boards on the inside of the room.
Surfaces Coated with the Wrong Paints
Bathroom paint is waterproof because it is polymer rich. However, sometimes people use normal vinyl or contract matt emulsion in bathrooms, and these paints remain porous. This means they hold onto moisture and effectively become a flowerbed for mould spores.
You should always use a suitable paint, otherwise you will always encounter problems with black mould. If you’re already having problems, then using anti-mould paints will help further.
Dealing with Black Mould in a Bathroom
Hopefully now you know why you’ve got an issue with black mould in your bathroom. I’m about to explain how to treat it and redecorate correctly, so the mould doesn’t come back. You will need to address any issues with ventilation and insulation before carrying out the below steps.
Shopping list
Zinsser Universal Degreaser and Cleaner
Zinsser Mould Killer
Zinsser BIN Aqua
Zinsser Perma White
Set the Room
Lay dust sheets on the floor. Cover the shower, bath, sink, toilet and any other bathroom furniture with plastic sheeting. Open a window; ventilation is important when working in an enclosed space.
Clean the Affected Area
Make sure you wear a mask (and ideally gloves). Spray the Zinsser Universal Degreaser and Cleaner onto every affected surface and then wipe with a damp cloth. Zinsser Universal Degreaser is a very strong product that can deal with far worse than mould, so you don’t need much. I sometimes spray it on the cloth rather than the surface.
Treat the Black Mould
You need to kill the spores to stop the mould from coming back. All I do is spray every surface with Zinsser Mould Killer and wait for it to properly dry.
Block the Stain
You may have cleaned and treated the mould, but it often leaves stains. You need to block these before you can paint over, otherwise it will bleed through your new paintwork.
There are loads of stain blocks on the market now, but Zinsser BIN Aqua is probably the way to go. It is fully water-based, so there won’t be any strong smell when you work. Zinsser BIN Aqua will create a barrier between everything that’s on the surface now and your new paint, blocking the stains and any odour.
Apply two Coats of Zinsser Perma White
Zinsser Perma White is one of the few anti-mould paints that I have absolute faith in. It’s waterproof, very durable, and contains a fungicide that resists mould growth. You can have it tinted to just about any colour, and you can use it on any surface, including ceilings, walls, and woodwork.
A Video Demo
How to deal with mould on a bathroom ceiling so it never comes back
This demo shows the best way to paint mould on a bathroom ceiling, but you can carry out the same process on the walls.
Final Thoughts
Mould is easy enough to deal with, but you do need to deal with it. The spores are harmful and can cause breathing difficulties if left unchecked. My hope is that this blog helps a few people to protect themselves and their families. Just follow this advice and use these products, and it should be a simple fix.
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