Rising Damp: in masonry occurs when ground water rises up the walls of a building by capillary action and is traditionally prevented by the insertion of a damp proof course during construction. The damp proof course is positioned level with the underside of the floor to form an impermeable barrier.

Symptoms appear as localized dampness in linear or patch form or widespread dampness which is highlighted on the lower sections of internal walls and the internal face of external walls. Internal plaster finishes may be damp, blistered or discoloured with "tide marks". Surface patches of water-soluble salts may be residue after moisture evaporates. Skirting boards may be affected by fungal decay, and if the floor is a suspended timber floor it may also be weak near the wall. Where the rising damp contains high concentrations of salts this may also cause extensive spalling and fretting of masonry where the osmotic pressure of "crypto-efflorescence" causes moisture to be continually drawn higher up the wall.

Damp proof bridging is a problem usually associated with new buildings and is caused by:

• Filling in the cavity above the level of the damp proof course e.g. mortar droppings and brick bats
• Earth where street levels have been raised and gardens cover sub-floor, reducing ventilation
• Concrete paths and verandahs laid without membranes are above the damp proof course
• Rendering over the damp proof course so that dampness may bypass the damp proof course
• Re-pointing decayed mortar joints at the damp proof course level without waterproofing additives
• Additions with failure of the damp proof course to meet up between the different sections of work or a complete lack of damp proof course in new work being keyed into existing work above the existing damp proof course.
• Existing damp proof courses may be fractured by foundation movement or hydrostatic pressure from a leaking drain or a raised street level.
• Rising damp in slab-on-ground buildings is evident in the form of patches on the slab surface or in the floor coverings causing decay, lifting or arching and frequently results from faulty slab construction caused by a lack of vapour barrier beneath the slab or adequate subsoil drainage.