How long should I leave wet plasterboard before patching?

[Gordsworth]

Hi,

Had a plumbing incident last week - upstairs bathroom heating pipe burst and flooded through to dining room below. Result is a nasty hole cut into the dining room ceiling (plasterboard) by the plumber who came to fix it.

My plan is to trim back round the hole and fit a new sheet of plasterboard, before skimming, papering and painting. However, I understand I need to let the bits around the hole which are still damp dry out before doing a repair. So I bought one of those electronic moisture meters (prongs), and after 6 or seven days of having a heater intermittently blowing at the damp area and two plastic dehumidifier packs in the ceiling space, the reading is down to 14%.

Thing is, I can't find a reliable source which indicates what an acceptable moisture level for plasterboard is? Do I have to wait till it gets to 0%, or is there a 'safe to replaster/redecorate threshold above that?

Cheers in advance,
Gordon

 

[roughcaster]

Any plasterboard significantly damaged by water is better being replaced, rather than wait for it to dry out. If the leak occured six or seven days ago, and you've had a heater and a de-humidifier on the go all the time since the leak, yet the reading is still showing 14% damp, the plasterboard must have been very wet to start with. Is the plasterboard foil backed or plain? If it was me, i'd mark out an area beyond the damaged/damp area, then neatly cut all the plasterboard away. You'll need to fit new timber/noggins in the exposed area, ready to fix the new area of plasterboard to. Check the thickness of the plasterboard as well, either 12.5mm or 9.5mm depending when the house was built.
Once you've removed the damaged area of ceiling, and fitted new noggins etc, measure and fit/screw the new piece of plasterboard into place, making sure there is plenty of timber around all the edges too for screwing into.
After that, tape and fill all the edges as required, sand down, decorate as required, and if done correctly, you'll never know there's been any damage at all.

 

[Gordsworth]

Hi roughcaster - thanks for the advice. I probably will take off all of the damp plasterboard as you suggest. Thing is, my moisture meter gives a reading of 3-6% on bits of the ceiling far away from the damaged bit, so it might be quite hard to determine where the damage boundary is. I'll probably take 3-6% as the 'pre-damage threshold' I was looking for.