Condensation mould on Bathroom Ceiling

Hi all,

I hope that you are well,

I'm new to the forum and a relative DIY noob so I thought I would ask for a bit of advice please.

We've had a patch of black mould appear along one side of the en-suite bathroom ceiling. I've doused all the surfaces in the bathroom with mould killer (Cillit Bang).

However, it became clear that the mould had appeared because a bit of moisture had got behind the paint as some of it in that areas was lifting when wiped and exposing the plaster underneath.

I'd done a bit of research however some feedback on my project plan would be appreciated please. Any recommendations would be heartily appreciated. This is what I'm planning to do.

1. Use a scraper to remove any 'loose' paint until I get to a point where the paint seems to still be firmly stuck.

2. Sand the points where this good paint meets exposed plaster with 180 or 220 grit sandpaper (I'm not sure which would be best) to create a smooth finish.

3. Cover with Zinsser Bulls Eye 1-2-3 Primer-Sealer.
- Should I use a roller or brush for this? If a roller what size?
- Should I just focus on covering the areas with exposed plaster and a bit over the edge of paint. Or should I do the whole ceiling with primer?
- Do I need multiple coats?
- Should I water it down?
- How long should I leave the primer before first coat of Dulux?

4. Paint - minimum two coats - Dulux Easycare Bathroom Paint Pure Brilliant White.
- I understand the whole surface should be done in one go.
- Should I do edges first?
- With a cutting-in brush? What size?
- Then roller the ceiling (9" roller). Or roller first then edges?

- B&Q comments for this paint suggest that it is very thick. I saw someone elsewhere suggesting to water thick paint down 10% to thin it just a little bit. Is this a good idea?
- How long should I leave between coats?

5. Finally as the ceiling is going to be rollered edge to edge I am assuming that it is worth masking to ensure I don't get paint on the (fully tiled) walls. I was planning to go all round the edge with 75mm masking tape. Should I paint all the way to the top of the tile? Or leave a bit of a gap if there is any sealant/grout at the top of the tile e.g. not paint that?

Planning to get all the stuff from Screwfix, most of the stuff from Wooster seems to have good reviews.

Thanks for taking the time to read. Any help appreciated.

Fix the source of the problem first. Extractor fan working?

Thank you for the reply.

I’d be surprised if that is the issue, it’s been a good 7-8 years since the ceiling would have been originally painted and the en suite shower gets a lot of use.

Is this abnormal? It’s a vent-axia unit and it seems to turn on fine.

What’s above it, if it’s a loft is there definitely no insulation gaps where the mould’s appearing?
Working extractor fan (used whenever the bath or shower is on), and insulated ceiling shouldn’t result in a load of mould.

It’s been cleaned off now but it wasn’t too bad. Along the edge nearest the window where the ceiling meets the tiles. Where it had been cleaned off there is a small amount of paint lifted. Concerned that more could lift if not treated.

it’s a New build, I was told a relatively good one during the independent inspection, Miller homes. We’ve been here six years and it was constructed a couple of years before (was the show home) so about 8 years it’s lasted.

There is a loft above but it’s not used for storage due to the new style efficient design etc.

I’m trying to see if I can get the fan grill off to check if it’s blocked with dust etc will Google it so I don’t break something

Can you not access the roof space above then? You need to know if it’s fully insulated with no gaps. They might have moved/disturbed some of the insulation when installing the extractor.
The mould getting worse, will happen as a result of whatever’s causing it not being fixed, rather than lack of redecorating it.

Forgive me, mould was black mould on an internal bathroom surface following a logical steam path.

It’s a small fully-tiled en-suite that sees a lot of moisture (my wife has very long thick hair that takes a while to wash and condition etc).

What would this have to do with disrupted roof insulation? No one has been in that loft for 6-8 years. We were told not to board it and use it for storage due to the design of the house, so never saw a need to go there.

Mould forms when hot moist air condenses on cold surfaces/cold air. Lack of loft insulation causes cold ceiling surfaces. Lack of decent extraction by the fan, causes much more hot moist air. Loads of threads on here about it, do a search. Just saying try and nail the underlying cause as well as redecorating

While you're up there, please photograph the fan and its markings, and the duct.

A more powerful fan will be available, and the duct might be loose or obstructed.

His long does the fan run on after you turn the light out?

Is it noisy?

Mold spores exist in every home , only adequate ventilation prevents them settling and the conditions they prefer (cold and damp).
No amount of remedial work will prevent mold .

23vc said:

Mould forms when hot moist air condenses on cold surfaces/cold air. Lack of loft insulation causes cold ceiling surfaces. Lack of decent extraction by the fan, causes much more hot moist air. Loads of threads on here about it, do a search. Just saying try and nail the underlying cause as well as redecorating

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Thank you... this all makes sense to me. I will have a look at the insulation aspect... although as this is the external wall and area above the window frame no less it's probably always going to be a bit colder than the rest of the room especially if the window has been open recently. May be better to see if we can improve ventilation.

JohnD said:

While you're up there, please photograph the fan and its markings, and the duct.
A more powerful fan will be available, and the duct might be loose or obstructed.
His long does the fan run on after you turn the light out?
Is it noisy?

Click to expand...

Thanks for the reply, yes its fairly noisy. I do think it's highly possible the duct is dusty at least. A clear-out may be a positive step. Likewise if it is possible to easily and not-too-expensively upgrade the fan that is also a possibility. I'll take a better photo and report back. I'm struggling to find a way to remove the grill at the moment!

foxhole said:

Mold spores exist in every home , only adequate ventilation prevents them settling and the conditions they prefer (cold and damp).
No amount of remedial work will prevent mold .

Click to expand...

It sounds like we are on the same page that improving the ventilation may be the best solution alongside the remedial works. Obviously I don't want the issue to recur in a few months if a dust-filled duct is allowing too much moisture to collect in the room. Perhaps either a good duct clear-out, a fan upgrade, or both. I'll try and get a better photo uploaded in the next 24 hours so we can look at that.

Thanks everyone!

If you photograph the grill/vent from all angles, someone may recognise it. Some have push-in tab that projects through a small slot in what would be the bottom if it was on a wall, you push it in with your thumbnail or a medium screwdriver.

Some of the modern extractors with ball-bearing motors and rubber mountings are amazingly quiet, and often more powerful.

Here is a better view of the fan.

Also did anyone have any feedback on all of the questions I asked in my project plan please?

Thanks again for the support.

daveforever said:

Here is a better view of the fan.

Also did anyone have any feedback on all of the questions I asked in my project plan please?

Thanks again for the support.

Click to expand...

I’d post the question in the painting and decorating section, more likely to get seen by the right audience

daveforever said:

Hi all,

I hope that you are well,

I'm new to the forum and a relative DIY noob so I thought I would ask for a bit of advice please.

We've had a patch of black mould appear along one side of the en-suite bathroom ceiling. I've doused all the surfaces in the bathroom with mould killer .

Click to expand...

This happened to me. I used bleach diluted with water, it hasn't come back. Now if the windows are ever steamy I open the windows but get into that habit regularly.