Again, if the dampness is more evident higher up the wall, wait for a rainy day, the heavier the better, go outside and check the gutters and downpipes for evidence of overflow into the top of the wall.
Falling damp is caused by moisture entering from the top of a property due to building defects and/or poor maintenance; for example, broken tiles or other roofing material defects and blocked guttering and down pipes. In addition masonry which has become defective with age as evidenced with damaged bricks and the deterioration of mortar courses and cracked renders.
Falling Damp has obvious visible sign in the form of a watermark which is created by blocked gutters and downpipes and is prevalent in periods of heavy rain. No salts will be present with falling damp.
Solutions for falling damp is increased maintenance and the repair of and/or replacement of obvious causes of ingress.