Spots on plaster coming through when painting

It’s PVA adhesive that’s been splashed onto the wall after it’s been plastered.

Could be ....pva Could be......areas that were overworked in the final troweling stages. But actually conjecture here without seeing first hand. General advice with areas of new plaster what will not take paint, is to roughen the area with 120 grit yellow, clean off the dust and then go over with some filler (easifill or toupret) Then sand to smooth and level, then re-mist coat with your paint for new plaster

Most probably, the pva adhesive has been mixed with a lot of water before it has been given to the wall surface, another factor that produces the splitting of the portion is the thickness. Normal plaster must have a thickness of at least 4 mm, when the thickness is thinner it can easily detach.

New plaster needs to be mist coated with a coat of contract emulsion (thinned with water to around 30%). And then once dried it needs 2 coats of vinyl matt or other emulsion of choice to acheive a solid finish.

New plaster needs more then one coat , depending on what brand of paint you use you will have to put at least three coats on all new plaster