Damp Walls (Internal)

[Alan H]

We moved into our new home 6 weeks ago and re-decorating have found in the living room we have damp walls. 1 wall adjoining next door, 1 our kitchen ( which is not damp?) and the other 2 walls lead to outside. We have noticed that the plastering up to around 50cm high has been renewed all the way around, and the walls are only wet that high up. They are not black, they are power white patchy. it also smells musty (yuk!). Next door say have not a problem?? Please does anyone know what this is?? The house is 80years old and in good nick this is the first problem we have come across and we have nearly finished the house. Thanx x x :? :? :? :?