Rising Damp

Damp Proofing

Rising damp is a common problem in older properties either because no damp proof course (DPC) was provided at the time of building, or because a physical membrane has failed or been ‘bridged’. In the majority of cases the provision of a remedial damp proof course is a cost effective and minimal disturbance option.

What is Damp?

Dampness in buildings if left untreated can lead to structural deterioration; it will result in decay of timber, spoil decorations and can have problematic health effects through the development of moulds and mites.

When an absorbent material such as paper, wood, cloth or brick is placed in a damp atmosphere it will absorb moisture. If the humidity changes the moisture content of the material will change with it.

Wet wall, Dry air

If a wall is wet, it will lose moisture to the air through evaporation all the time. However, constant water rising through the masonry will cause damp patches, salt marks along with associated mould and fungal growth. Typically this is caused by the absence, failure or bridging of the damp proof course.

Salt contamination due to Rising Damp

The source of rising damp is the soil or subsoil which are always wet. Soils consist of biodegraded plant matter hence water in soil is not pure and usually contains nitrate, chloride and sulphate salts. These rise through the masonry and are left behind as water evaporates. Rising damp over a number of years can cause high levels of salts in masonry. These residual salts are hygroscopic; hence they contribute to the problems found.

The AAWU provide equipment to test for damp in masonry such as using Protimeters and calcium carbide testing  as well as providing laboratory analysis to test for salts in masonry.

Rising damp results from the capillary action of water from the ground. In the absence of an adequate damp proof course an area rising to around 50cm (or more) above the skirting level along the whole length of the wall will result in damp patches and discolouration. Where the damp proof course is damaged or breached, patches of dampness may occur.

Damp Proof Treatment

Initially the damp proof course needs to be renewed. The AAWU use the latest range of BBA Approved remedial Damp Proofing products. Before treatment it is necessary to remove the plaster to ensure the hygroscopic salts are removed.