My house is around 150 years old and in one of the ground floor bedrooms, we have strange damp spots on all the walls that are external. Have included a picture to show the worst of it. As you can see it starts near the skirting board but does not fully cover the area then it rises into circular patches. Has anyone seen this before? As I would really like to get the walls repaired. The walls are papered in plain white as they were quite rough then painted over. As you can see the paint in flaking off. Any help is greatly appreciated.