Vinyl matt paint on new plaster :-/

[Marc1912]

I've realised that a few months ago I painted a newly plastered wall in my extension (old style plaster, not plasterboard) with vinyl matt emulsion paint. I asked shop for standard flat matt paint, they gave me vinyl matt, which was not what I was expecting or thought I had asked for. I didn't read the label till too late.

The wall was left for a few weeks after plastering, it was visually dry —nice uniform light pink— when I painted it.

Now I'm finding that a couple of pictures on the wall have gone mouldy. Moisture reading of plaster is 18%. I guess wall still has some moisture from the build as there is no sign of any damp problem apart from that.

I guess I have messed up. I'm hoping that when heating comes on in autumn it will dry out and all will be well, but obviously vinyl matt is not breatheable. But still surely some moisture must be getting through the paint or the pictures wouldn't be mouldy?

Should I do something about it now, or hope that it corrects itself in time?

Thanks

 

[opps]

What did you expect when you asked for standard flat matt?

The vast majority of emulsions sold in the UK are vinyl (AKA acrylic or latex).

I am a decorator and tend to work in London. Typically the older properties are Victorian 9" solid walls. Historically they would have had lime plaster, but over time they have often had gypsum skim coats.

Are the pictures moldy on the wall side, if yes, there is probably still moisture being released from the plaster. Vinyl paints do allow some moisture to permeate through, not much, but some. If they didn't, you wouldn't get water stains leaking through.

You might have been better off with a low latex paint, it allows the moisture to evaporate off with greater ease. They are however impossible to keep clean, and if the plaster was still releasing moisture, you would have mould behind the pictures regardless.

The pictures are preventing airlow over the plastered surface, hence the mold.

Take the pictures off, leave the windows open. put them back up in a week or two and see what happens. If you still have mold, then it may be a result of excessive condensation or water ingress.

 

[Marc1912]

I expected old fashioned breathable matt paint, though oviously I am out of touch! Thanks for the advice, will try that and see how it goes ...