@jeff,I will answer what I can. Guttering is fine, no issues, surrounding ground is solid concrete and tarmac. As for breathable plaster, I don’t know. The area of damp is behind a kitchen unit (corner), same wall as the radiator, just above the skirting board. The wall is exposed to the elements. A dry stone wall from outside meets the wall where it is damp, not sure if this may be a problem area.