Walls after water ingress

[NearlyDIY]

I live in an old property, with lathe and plaster walls. All external walls are covered in lathe and plaster, whilst the internal ones are all brick.

One room has two internal, solid brick walls, and two external, lathe and plaster covered walls. At sometime in the past, there has been water ingress issues in the room which has affected the ceiling and a portions of the two lathe and plaster walls, as well as a section of the brick wall.

The external issue has now, hopefully, been resolved and should cause no more issues. However, will the walls "dry out"?

Both walls have what looks like lining paper on them, which has been painted over with white emulsion. On the areas where there appears to have been some kind of water damage, on both the lathe and plaster and the brick walls, there appears to a powdery substance covering it. This I am guessing is the emulsion, but what specifically about it is causing this? Are the walls drying out, causing the paint to go this way, or is there something else afoot?

Help appreciated

Duncs

 

[Burnerman]

Unfortunately plaster doesn't like getting wet, Duncs......it changes somewhat and doesn't return to its original state.
The dust you see is likely from that plaster rather than the paint.
Is it possible to have some of the plaster redone?
John

 

[foxhole]

Water stains cannot be painted over without first using a stain block or any stains will bleed thru, even 20 coats of emulsion.