Generally old buildings or barns suffer from this type of problem as usually no physical type of DPC - Damp Proof Course was ever installed.
Minerals in older construction materials and problems with damp on exterior walls can lead to salt contamination on plaster and render. This high salt level then leads to more moisture begin absorbed into the plaster which will lead to staining or can damage the plaster by extending damp. Not treated area within the time will lead to damp walls all the way through.
We can offer our help preventing salt contamination on damp walls or from the ground water from damaging basement tanking, render or plaster with our professional treatments.
Give us a call on 077141 87053 or book your Free Survey and we will come and help you to deal with it.