Our house is built on a slope and their is a bit of a white (possibly salt) line appearing on the gable end. The roughcasting is needing replaced and abuilder has suggested that the mark might be rising damp resulting from the tarmacaddammed drive - no space between tarmacadam and wall. He also suggested it might not be major concern as line proobably not height of inside floors (due to slope). What should we do? thanks :?