Treating plaster - damp caused by shower leaking overhead

fifthofwhisky

I have a minor leak (a drip rather than a flood) that over a year or two has caused ceiling plasterboard in the room below the shower to get damp. I've removed the bath/shower surround to investigate and found some softening of the plaster, and the paper backing has come away (not sure what type of backing but its not waterproof or water resistant). There is yellow staining on the ceiling/wallpaper in the room below where the water has run (about 80 cm away from the source). There is also a small amount of blackening (patchy, with a few spots here and there), which is most likely damp. The damaged plasterboard (particularly where it is soft) has gone through about 1/3-1/2 of the thickness in spots (an area about 15 cm2), but hasn't gone further with only the yellow water discolouration showing on the papered ceiling. It's easy enough to dry out with the bath/shower panels removed I have easy access.

I really don't want to pull the plasterboard down so I was hoping there might be some treatment options. Are there any? 

Doozergirl

We know it's 'damp' because it's wet. 'Damp' isn't some separate phenomenon to being wet.  It just describes a wet thing.  There's this feeling that 'damp' is a noun.  It isn't really.  It seems to have evolved that way in the building trade for people to sell stuff you don't need to treat it.  

The black stuff is mould from the humidity in the air condensing on the cold, wet patch. 

Is it still wet?  You could just let it dry, sand it back if necessary and put stain blocker on it before repainting. 

Otherwise, if it has dried out and the plasterboard is genuinely shot,   you just remove the affected area of board immediately around the marks, leaving some joist exposed for the new fixings to go to and add in a new piece of plasterboard and blend in the skim.  Not a great deal of work.  

FreeBear

Plaster, as used in plasterboard and the pink stuff that is usually skimmed over the top, is made from Calcium Sulphate - This is mildly soluble in water, so it turns to mush if left damp or wet for a long period of time. You may well get away with using a stain blocker on the ceiling and then repainting.. In the bathroom/shower, I'd suggest replacing the plasterboard with a waterproof cement board. But if it is hidden behind the bath and you want to save some major disruption, put the panels back on and leave it hidden from view.

fifthofwhisky

Thanks for your inputs. On closed inspection it's not so bad because most of the water (a drip) ran through a gap to the wall in the room below. There is minor degradation of the plasterboard but I think it will be OK to use stain blocker and patch it up. The shower is being moved anyway and I'll consider materials as suggested at the new location.