I have a top-floor flat in a Victorian building that has had a damp patch on an exterior wall since I moved in (unfortunately not picked up in the survey). The stain is diagonal, which suggested to me that water was getting in through the chimney stack above. But I have been battling with my freeholder who thinks it's condensation as this bit of the wall is directly opposite the kitchen (which has no door).
We have tried using a dehumidifier to no avail. Work on the roof showed the chimney stack and roof were largely OK. A vent has been put in and the patch seems to be drying out a bit but ... slowly.
Does anyone know: How long stonework takes to dry out? How I can get somebody reliable to check it out who isn't biased? Whether I can speed up the drying process with any special paints, etc.?