Painting a mouldy ceiling

[Jason]

Hello

I had some black mould on a couple of my ceilings, and I've cleaned it off with bleach. It all seems to have gone/died, but I've been left with dark grey stains where it was.

Obviously I've got to repaint the ceilings now, but I was wondering if normal emulsion will be enough - is it likely to come back or stain through? I've seen fungicidal paint for sale from (amongst others) Screwfix, but is that overkill? Would an oil based primer covered by normal silk emulsion do the job?

Thanks in advance.

Jason

[Andrew Gabriel]

Bleach might temporarily kill it and 'bleach' the colour out, but bleach isn't a cleaner.

It will come back unless you find and fix the cause. The ceiling is damp. Moisture might be coming through from above or the walls, or it might be condensation. Some description of the ceiling construction, what's above it, where it is on the ceiling, what sort of rooms it happen in, ventilation in the house, etc might help.

[Jason]

Hi Andrew

The cause seems to have been a broken extractor fan in the bathroom - it was all alright until the fan died. The worst-affected room is/was the bathroom.

The ceiling is just plasterboard with textured paint/artex and emulsion on it. The attic is above it, and there are no leaks in the roof. The house is double glazed, so the ventilation isn't fantastic anyway.

Cheers

Jason

[Andrew Gabriel]

Is there any loft insulation? If so, is it missing in the damp areas, or not laying properly on the ceiling, resulting in cold spots?

Is there a long term source of moisture in the house, such as lots of damp cloths hanging up to dry? Although showers and baths generate moisture, the proportion of the time they are used is unlikely by itself to cause the problem, even if the fan is not working.

If the double glazing has trickle vents, I suggest you make sure they are open in all the affected rooms. Otherwise leave some fanlight windows locked in the slightly open position.

[meow2222]

If what caused the mould is still happening, it'll reoccur. Mould killing paint really helps though, at least for n years.

To make it... Finely crush 16 aspirin and add to 2.5 litre paint, give it time to soften and disintegrate, and stir thoroughly. If you have any copper compound around just a small pinch of that as well would give even more mould protection.

If stains come through, a layer of oil paint stops most stains. Failing that there are stain block paints, but theyre not usually needed.

NT

[Stuart Noble]

What's the chemistry behind that then?

If you have