One of those days where one job leads to another...
I went into my lad's room, to investigate a loose shelf. The bracket was starting to come away from the wall, there was some paint on the bracket from when I last painted the room (18 mths ago). I pulled at it, and to my horror a six inch square 'sheet' of it came clean way from the wall, revealing bare plaster. I pulled at the rest of it, and ended up with this:-
Known history is as follows:-
House built 1985
The outside of that wall faces East, there's no evidence of damp (at present).
At some point between 85 and 2000, the upstairs rooms where reconfigured. There was a wall I think about three foot to the right of the present wall alongside the bed, you can see the different colour plaster.
We moved into the house in 2000. I can't remember what colour the wall was, but I painted it navy blue (you can see that paint where the LH shelf bracket was).
18 months ago I repainted the room white with some Crown paint.I'm not sure what to do. Do I need to get the rest of the paint off that wall, or can I just sand and rub down the existing boundary between paint and plaster and paint over the whole lot ? What do I need to prime the plaster with, before painting ?