A damp-proof course (often abbreviated to DPC) is a horizontal barrier in a wall designed to resist moisture rising through the structure by capillary action - a phenomenon known as rising damp. A damp-proof membrane (DPM) performs a similar function for a solid floor.

Rising damp in theory can occur for various reasons - the failure of an existing damp proof course, bridging due to the raising of external ground or internal floor levels, or in older buildings, the complete absence of a damp proof course.

In practise, damp proof courses almost never fail. Proper diagnosis of the reasons for dampness will always show one or another of a variety of causes - usually condensation from human occupation, or sometimes penetrating damp (leaky gutters, broken drains, cracks in walls) or ground levels higher outside than the top of the internal floors.

Other causes of rising damp are the availability of ground water, the porosity and pore size of the building material and the thickness of the wall.

The most common forms of rising damp treatment usually involves the injection of a siliconate type chemical either in the form of solution or cream, another option is an active Electro Osmotic system. Dependant on the thickness of the walls, this is usually done by drilling holes in a band around the affected wall and injecting the recommended chemical or cream solution or installing the Electro Osmotic system.A physical rising damp membrane to form a new damp proof barrier is also an option.

Afterwards, any salt contaminated plasterwork should be replaced. If the plasterwork is not properly removed and replaced with specialist salt retardant plaster, the salts that are present in the plaster may continue to absorb moisture from the air even after the installation of a new retrofit damp proof course giving the appearance of dampness.

Professional rising damp treatment

At BDS Southwest, our fully qualified and experienced surveyors are experts at identifying and treating rising damp and will arrange for a suitable solution for your rising damp problem. After an initial property survey and confirmation of a rising damp issue, our professional surveyors will propose a rising damp solution that best suits your property. It can include:

Chemical damp proof treatment

Recommended for most types of walling, it involves the injection of chemical under pressure into holes drilled at intervals into the wall at levels decided where practical by our surveyor at the time of a property inspection.

Injection mortar/creams

Ideal for many applications and particularly good where a good sized bed joint is visible, our injection creams are injected under low pressure and is carried by rising damp into the mortar beds and rubble where it crystalises to form an impermeable rising damp barrier.