Hi
Can you confirm if the wall is plastered or plasterboarded?
If it's bare plaster then we have a project covering everything you need to do to prepare bare plaster for painting:
https://www.diydoctor.org.uk/projects/p ... laster.htmIf it is indeed actual plasterboard this is a little trickier but again we have a project on
https://www.diydoctor.org.uk/projects/d ... rboard.htmWhen painting plasterboard, essentially you have to seal it first due to the fact that it's so porous. This is best done by giving it a few coats of SBR (construction grade PVA). Once dried it can then be painted over.
Unfortunately any damage will be a bit tricky to repair. Normal practice would be to fill the damaged areas and then sand them back flush with any surrounding areas, but unfortunately if you catch any of the surrounding plasterboard surface, the sandpaper will damage this also leading to an endless amount filling.
Ultimately the best course of action is to have the whole surface plastered but this can be expensive, so the next solution would probably be to cover the surface with a lining paper and then paint over that
Kind Regards