Plaster peeling on second coat after first mist coat taken

Bendy_House

The plasterer may have used PVA to bond the new skim to the old - that's common practice, and not an issue. This PVA would therefore be at least 3mm deep under the new skim, so is just not an issue when it comes to painting. Only PVA which is somehow on the surface of the plaster will cause a problem when paint goes on it. There is nothing to suggest that there's PVA on yours - it would be a partially shiny skin, and would peel if sanded.

So, for the new skim yet to be painted, if it's nicely matt and not excessively polished, then all it should require is a good wipe-down with a damp cloth to leave a clean, dust-free surface. If you want to be doubly sure, then it's probably worth getting a large (half-sheet size) hand-held sanding pad and pole, and some 180 grit paper. Lightly go over it all. This will remove any bumps and tramlines (there's bound to be some) and also 'key' the surface. Then wipe down with a damp cloth.

Now apply just one mist coat.

Once 100% dry, apply your first proper coat.

This should work. You should not have any issues.

Is the room well ventilated? Why did the other coat take so long to dry? Close that room's door, and open every window in it at least half way. If it only has one small window, you may need to also open the door to allow a good through-flow.