The ceiling has probably been painted over fresh plaster without a mist coat
being applied – dry plaster can suck out the moisture from the paint preventing it from bonding correctly and results in flaking, especially if there is moisture in the room.
The decorator first applies a mist coat
on to the new plasterwork, partly to seal the absorbent plaster but also to show up in relief all of the humps and bumps left by the plasterer.
Peter Christian, by email I'D 2 useapole sander then give the ceiling a mist coat
of white paint and use a pencil to mark any defects.
Owing to the quality of the finish, the parts need only a single mist coat
of water-based paint.
Then give the ceiling a mist coat
of white paint, take a pencil and mark any defects on the ceiling.
Give the walls a mist coat
of emulsion paint, apply a stain block over any marks and finally give two full coats of paint.
When the ceiling has been washed down, apply one mist coat
and two full coats of emulsion paint.