Damp repair - how much plaster to take off?

[HarryUp]

I’m helping my daughter sort some issues with her flat (a basement georgian flat but extensively renovated and replastered fifteen or so years ago), one of which is an area of damp caused by water penetration from an overflowing down pipe hopper and possibly also through a window cill.

I’ve taken the rad off, removed the slightly mouldy skirting board and the blown skim coat. The base coat underneath feels slightly damp but is still firmly adhering to the wall and there is no sign of salt movement or softening. The question (at least for now!) is whether simply reskimming is going to be ok, or should it be taken back to brick?

 

 

[twice round the block]

If you tap the plaster with knuckle and it doesn't sound hollow you should be OK just to skim