@LukeAlmighty @tomie Outside wall too cold. Inside air too damp. Water beading on the wall every day probably.
Choices are get rid of water in the air, heat the entire wall up, insulate the wall or paint the wall with anti mold paint.
1. Rip the cupboard door off. Keeping it closed means the wall will never dry. Dehumidifier if free electricity
2. Heating probably out of the question
3. Buy good water tight insulation that bonds directly to plaster. No beading if warm air dont touch wall
4. Live with the water but paint the war with toxic paint. (Cheapest, ask for samples to match color, must be anti mold/moisture)
@tomie
Let's not jump to any conclusions...
I like to not cross any option out too early.