We recently bought a 1920s property in Yorkshire. The guttering on the north wall failed over the winter and there was rainwater running down the wall (mostly close to ground level) which has resulted in, or exacerbated, penetrating damp in that part of the exterior wall and about 1.5-2m (at its worst) into a connected interior wall on the ground floor.
I planned to remove the wallpaper, let the wall dry out for a few months, prepare the wall and paint it. However, having removed the wallpaper, underneath I have found several layers of a very glossy, almost plastic-y paint that I assume is some sort of damp-proofing product. I'm fairly new to this and if anyone can explain what it might be, what it does, and what the best course of action is and why (should I leave it alone? Remove it? Remove it and replace it with something similar?) it'd be appreciated. It's glossy and smooth enough that I assume I'd need to prepare the surface somehow before painting.
I mention the house age as it's difficult to know when this was added - I'd guess at least 20 years ago and maybe up to 70. The different layers are different colours so it may have been periodically re-painted over a long period, and in one small area by the back door a layer peeled off to reveal very slight mould growth between it and the next layer down.
(I am also very aware that if this was added to fix damp problems decades ago then the recent guttering damage was not the only reason for the penetrating damp, but I wanted to avoid making this question too broad - will add a separate linked question shortly.)
