The Normal levels of damp –
Plaster – .2-1%
LIghweight concrete – >5%
Timber 10 – 20%
Test for Damp: By sight, smell, possibly taste, touch and sound. A calibrated damp meter should be used as follows: Electrical Capacitance as a guide to damp below the surface and when located by electrical resistance as a guide to damp on and just below the surface.
Pictures below show spatter caused damp, a dripping overflow pipe has caused substantial damage to this property, rising damp, penetrating damp etc