Blistering paint on plaster

[JohnLIreland]

I've just moved a door and have plastered over the wall where the old door was. I sealed the newly-plastered area with a PVA/Water mix and I'm emulsioning the whole wall but I'm having problems with patches of blisters, both over the new plaster and the older, previously-painted wall. If I remove the dried blisters, patch them over (with a propriety filler) and paint again, they keep coming back in different areas (both new plaster and old plaster areas). I've just repaired the last lot in the wall, wiped away the dust with a damp cloth and more have appeared.
I know it must be something to do with the initial, base preparation of the wall that went wrong but how can I get round them without stripping back to the bare plaster again?

[thebreeches]

I don`t fully understand what you have done! are the blisters under the plaster or the paint?having qualified as a plasterer several years back hopefully this advice might be of help. If the blisters are in the finish coat of plaster these can genreally be "trowelled out" as it sets hard these are caused by trapped air as you lay the plaster onto the backing coat (which has been applied to the brick/blockwork) all you can now do is as you say to scrape and fill them. If the blisters are under the paint then this is caused by lack of adhesion such as dust if you applied a pva as you say you have you may have mixed it to thick and has formed a skin which is peeling off under the paint causing it to blister. This pva is now going to be difficult to remove you really only have two options . Continue to remove and fill the blisters or scrape the affected areas, apply a pva (to give a key) over  the wall and whilst this is still tacky re-skim the wall using a multi-finish plaster, approx 5mm thick.. quite drastic I`m afraid...