You probably have old white wash or distemper on the ceiling. You will need to apply one coat of primer sealer and can be decorated over with any finish. Do not put pva on it, this will create further problems and work and plaster skimming will not adhere either long term.
A.L.SMITH DECORATING, Essex, Est 1980
First clean good whole celling with sugar soap then use primer I recommend Zinasser blue one then u can go ahed and paint celling with good quality paint recommend dulux trade
Painting and decorating
Hello... I myself have had this problem to which I used a stabilising primer.
This is not that inexpensive and also depends on the size of your ceiling.
Then once It was dry I applied two coats of emulsion.
Stabilising primer can be bought from most decorating centres.
B J Lenehan