We have a 3 year old house where the builder's decorators have done a
poor job on the first painting of the plasterboard walls. Now that I'm
getting round to redecorating, several areas of paintwork show really
bad adhesion and start to flake off when they are painted over. Is
there any way to remedy this without resorting to removing the bad
paint - I was thinking about applying a very dilute PVA wash over the
bad bits, and hoping that this would penetrate the paint layer. (The
paint does seem to be a bit soluble already, as wiping with a damp
cloth does take some off.)

Ideas?