I live in an end terrace built in the 1800,s and the final work to be done was in the rear bedroom, the rear wall faces south and is over the flat kitchen roof, after stripping off the paper one small area of the plaster three foot in from the gable end came away, there had been no hint of dampness through the paper so i assumed it must have been due to it being old plaster, i did note though it had been damp proofed using sand and cement, this must have been 20years ago at least before i moved in, again there was no sign of anything being wet. So i had the ceiling re boarded and the room skimmed, after the plaster had dried out i started to notice a small damp patch appear in said area, i thought it might be the plaster not fully dry, after a couple of weeks it seemed to dry a little so i used a little zinsser to cover that patch. Over a few more weeks i noticed nothing had come through the paint but a little damp had crept out the side of the painted area and there was a line where salts had appeared. The outside wall pointing had been in need of repair and this has been done which seemed to highlight the patch. The rest of the wall from top to bottom is fine so i would think that rules out the guttering which i recently cleaned out, and the roof as this patch is at the bottom of the wall. So is it possible after pointing the wall could be drying out? I know the plasterer who is very good and hes coming to have a look, would it be feasible to have a damp membrane installed on that wall? That was done downstairs but i never thought about damp in upstairs rooms, there is also no central heating pipes as the radiator is on the side wall and the pipe runs straight down into the kitchen and there is no drop in pressure. Just looking for a few opinions and possibly something i have not thought of.
Cheers.
