I have a 1930s semi with solid brick wall construction. The 1st storey is stoneclad but has not been painted in many years (project for the summer). Today we noticed black mould running from skirtingboard to about 1.5m above the skirting in the corner (both walls making the corner are external). The walls feel damp to the touch and there is a chest of drawers in that corner (otherwise we might have noticed earlier). There is a ground floor extension which has flashing to the cladding running along one of the two external walls, so I wonder if it could be ingress at the flashing join?
I haven't been able to have a close look (had a hernia operation yesterday) but I can't see any visible defects.
Has anyone any ideas what might be causing the problem or possible solutions? We noticed this problem in another room last year inside a built in wardrobe, but since removing the wardrobe it has resolved.