How should I treat dump on external wall internal surfance, facing north,? I am at the 4th floor of council building

Hi, I'ts extremeley hard to give advice regarding Damp Proofing without seeing the problem with my own eyes, from your description, it would seem that your walls are suffering from 'Condensation', single skin walls in winter can become extremely cold. We term October to March 'Condensation Season', when outside temperature's drop, external walls cool down and any moisture whithin your home will condense against the cold surface. Installing more ventilation could help the problem, if not, a product called 'SempaTap' could do the job, this is basically a thick foam that is applied like wall paper, this will warm your walls up to a temperature that condensation cannot form. If you get a cold bottle of milk or wine etc out of the fridge and leave it to stand for a few minutes, you will see moisture appear on it, this is from the invisible moisture that is in the air, it's exactly the same principle that happens with cold surfaces in your home.

Hi there You probably have a condensation problem although you do not mention mould if this is the case you need to treat and paint with the right paints and better ventilation as the first course of action or insulation boards on these walls to warm up the wall. damp does not come and go with the seasons

The external wall insulation will also increase the temperature of the internal surface of the wall, making it less likely that you will get condensation problems on your walls. 95% of it will help you, as well as external wall insulation will reduce the heating cost up to 45%