Painting old new plaster

There is such a thing as plaster primer, it wouldn't harm to use it. It's a regular over-the-counter product, although almost everybody uses watered down emulsion as a first coat. I have seen decorators use watered down wallpaper paste but I wouldn't recommend it. The 'trade' emulsion I understand is breathable because it allows a builder to decorate before the plaster has fully dried, which isn't your problem.

You need to wonder if the paint is coming off in sheets if there might be a damp issue.

TW

Uncoated plaster is absorbent, & sucks the glue solution from the first coat. Give it a quick coat of water, wait 5 mins & paint with undiluted emulsion & problem solved. Sure, there are more difficult/complex/pointless options too.

It's bone dry, so damp is not an issue. But seems like there's a thin layer on top of the plaster that's flaking off and causing the paint to come away:

Whatever this layer is, I can help but think it's going to need rubbing back to the underlying plaster.

Theo

It could be distemper.

I had this issue when I had a upvc back door fitted, a great chunk of plaster fell off the wall alongside where the old door was removed. In the end a friend of mine used some cheap lining paper and then painted onto that, It has never had a problem since, though one part is now just begging to have a bit of a bubble its lasted over 10 years. Brian

Possibly an alternative solution which may be less work

Lightly abrade away the flaking paint

Cover with a lining paper BUT use something such as Erfurt White Wallrock Fibreliner Wallpaper

Ive seen it (PVA) do that, or simply paint that was too thick on bare plaster, didn't soak in and never keyed properly. The advice to put on a 'pisscoat' on bare plaster, is valid.

As is the advice to use sugar soap when repainting to degrease the surface, especially in rooms that have seen a lot of cigarette smoke: That can easily put a greasy or waxy surface that will allow paint to flake off.

I'd try degreasing with the sugar soap fisrt and then if it still feels slick roughing up with some fine wet and dry

I thought you said less work!

I take it that you have never tried to get PVA from a wall, especially if what is under it is capable of sucking up more water.

When sanding through the paint and the PVA the resulting surface probably will not worth painting and a skim coat of a fine filler will be required

I have, but normally avoid it

Why you're in favour of making life so hard I don't know. Mass peeling means the paint went on bare dry plaster, no pva

I discovered the hard way that pva on plaster does prevent emulsion paint from sticking. John

It sure does if you use too much. If the plaster's not crumblig you don't normally need it.

That's not necessarily the point the OP was raising. The plaster will/may not have needed PVA prior to painting but if someone PVA'd the wall before painting then his peeling paint may/will be due to this. Alternatively, painting new plaster without the mist coat first may also have caused the problem.

If the OP is repainting what is the best method to ensure that the problem doesn't reoccur. You have come to the conclusion that the paint was incorrectly applied to dry plaster, with no PVA. The OP seems to think that maybe the wall was sealed first with PVA.

In either case its virtually the same thing. Paint is prety much dilute PVA type material with pigments in.

Peeling is down to one of tow things IME.

The first is that the first coat of PVA or paint was applied to thick or at too high a temperature so never penetrated into the plaster. That rips off leaving bare plaster behind. The solution is a dilute coat of something before applying the final paint layer.

The second is that the last coat of paint has not adhered to what was there already, due to it being old, hard and probably greasy. In this case what is behind the paint is not bare plaster, but a slick surface. Sugar soap plus a light sanding with a decorators sanding sponge sorts that out.

it could be either, or other. Point is that glue sucked out of the paint layer is many times more likely than other options.

I think we answered that

No, I concluded, fairly I think, that glue sucked out of the paint layer is many times more likely than other options. Either way a water coat before full paint should work ok. (If it turns out the op does have a pva slick, he'll know very quickly, and will either persist with slow success or ask for more advice.)