I have had a serious leak from my water tank in the attic. The water leaked into the bedroom ceiling and living room ceiling down stairs. Can someone tell me if the plaster board ceiling need replacing even though they are now dry? I have been told that their itegrity is now compromised?
I would say yes, or maybe just cut out the affected area. Gyproc is like a sponge, soaking in the water. If it was a small amount of water then wait till its dry and undercoat the water mark then repaint.
if it's still flat, not coming away and perfectly dry then it's probably OK.
you will most likely need to apply some kind of damp stain block such as Aquaseal to stop the damp patch from grinning thru your fresh paint - and it will without treatment regardless of how many coats you apply.