A patch of brickwork on our external wall appeared last year and again this year following heavy rainfall. The gutters are clear. The house is 20 years old, is block and brick with a cavity between. Cavity wall insulation was blown in 10 years ago. There is no sign of damp internally.
Any clues as to what's happening, why the damp patch (the mortar is damp to the touch) appears, what we might do about it; all gratefully received.