There are many types of damp problems, all caused by different things and all rectified with different methods.
Common damp problems are;
This is dampness that seeps through walls from the surrounding earth or by rainwater penetration.
Caused often by a combination of dampness and insufficient ventilation
It is caused by water rising, through capillary action, in the porous material of which most walls are constructed.
Wet rot decay is normally restricted to excessively damp timber and can be easily mistaken for dry rot in certain circumstances.