Rising Damp

The source of true rising damp is capillary ground moisture climbing up through the internal pores of the masonry carrying damaging ground salts in solution. Moisture finds its own level and once the masonry has become saturated the moisture level rises with the lower masonry always being the wettest. Only when the masonry has been fully saturated does the moisture rise and at this point the masonry will be equally wet on both sides of a solid wall or both leaves of cavity brickwork sharing a common damp-course. Rising damp can be caused by the absence of an effective damp-course or by “bridging” of the damp-course.

As the moisture evaporates from the surface a crystalline surface salt “efflorescence” deposit appears on the exposed surface. Salt attack is the decay of masonry materials such as stone, brick and mortar by soluble salts forming crystals within the pores of the masonry. As the salt crystals grow the masonry is disrupted and decays by fretting and loss of surface skins. The salt commonly comes from the soils beneath and is carried up into walls by rising damp. When the dampness evaporates from the walls the salts are left behind, slowly accumulating to the point where there is sufficient to cause damage. Repeated wetting and drying with seasonal changes leads to the cyclic precipitation of salts and the progressive decay of the masonry.

Rising damp requires support from sufficient soil moisture content and natural active water table content. Active “rising damp” will not occur during extended periods of severe drought and in many cases months of above average rainfall is required to bring up the water tables and soil moisture contents to induce and support rising damp.

Visible Symptoms

• Blistering
• Salt-ridden, bubbling and flaky paint
• White salt powdered residue
• Powdery disintegrating mortar and plaster
• Rotting timber skirting-boards and door-frames