Rising Damp, is caused by moisture passing through a permiable wall, the moisture is derived from ground water.

The moisture rises through the pores (capillaries) in the wall by 'capillary action' which act like a wick.

This type of Damp is normally due to defective Damp Proof Course (D.P.C)

Penertrating Damp, is caused by moisture penertrating the pores in the wall.

This type of Damp is normally caused from some forms of defect in the structure ie. pointing,  defective guttering and even ivy.

Hydroscopic Damp, is caused by salts being deposited into the wall at some stage of the buildings life. This could be from unwashed sand at building stage to old chimney soot build up.

The salt deposits draw moisture from the air, this type of Damp can occur at any height.