Lateral Damp can be described as moisture forcing its way through a wall. (Rising Damp is moisture moving from the ground up through the masonry). The illustrations will help you understand different occurrences of Lateral Damp.
You can expect to find lateral damp if the tanking material - that is, the vertical damp proof course - has deteriorated or if it has been omitted or incorrectly installed. Some sypmtoms of lateral damp are the appearance of salts crystallising on the walls, flaking or blistering paint, and deteriorating plaster.