hi customer has got a little problem with condensation on bathroom ceiling (lots of litttle black spots) i assume from lack of an fan/extractor in the room.ive told her she needs one in really and shes getting that done.the ceiling in general is very old (with also what looks like destemper paint on ,so was going to over board it,would i be better using foil backed boards to over board it?,thanks for any advice offered lads,regards les