Rising Damp (Salt Damp)
Rising damp (or Salt Damp, as it is known in many parts of the world) is not the most common form of dampness encountered in buildings; this is left to condensation. However, a high proportion of older buildings are affected by rising damp to some degree or another, as shown in the graph below:
Rising damp in buildings occurs when water from the ground rises up through the bricks and mortar of a building by a process loosely termed as "capilliarity." In simple terms, the water rises up the wall of a building in the same way that oil rises up through the wick of a lamp. This effect can be seen in the time-lapse video below showing damp rising through a Victorian brick over a period of approximately 36 hours:
The height to which the water will rise depends on several factors including pore structure of the bricks and mortar and the rate of evaporation. Masonry containing a high proportion of fine pores will allow the water to rise higher than a coarse pored material.
Ground Water and Hygroscopic Salts
Ground water contains soluble salts, the most significant of which are chlorides, nitrates and sulphates. When rising damp occurs, these pass with the water up the wall and are left behind when the water evaporates. Over many years of active rising dampness large quantities of these salts accumulate within the masonry and decorative surface, most becoming concentrated in a general ‘salt band’ towards the maximum height of rise as illustrated in the diagram on the left. Both chlorides and nitrates are usually hygroscopic, (i.e.they can absorb moisture from the surrounding environment) and, in general, the greater the amount of salts the greater the absorption of moisture – especially under humid conditions. Thus, even though rising dampness may have been controlled by the insertion of a remedial damp-proof course these salts alone can cause the wall and any contaminated decorations to remain damp. It is for this reason that specialist replastering is such an important aspect of rising damp treatment. Further information on replastering as part of a rising damp treatment strategy can be found on our replastering as part of a rising damp treatment page
Treatment of Rising Damp
Treatment of rising damp (known as "damp-proofing" or "dampcoursing") typically involves the installation of a chemical DPC, such as Dampcheck Plus using specialist injection equipment, followed by replastering using a Refurbishment Plaster or a salt retardant render incorportaing Renderguard Gold. However, with the introduction of Dryzone Damp-proofing Cream, the process has now been simplified. The Dryzone system is based on a high-strength damp-proofing cream that is injected into holes in the masonry without the need for an injection pump.
The video below explains how rising damp occurs and describes a treatment strategy using Dryzone damp-proofing cream (includes audio commentary):
Rising Damp in Floors
Free Damp-Proofing Book
The identification and treatment of rising damp is dealt with in full in our free publication, "Rising Damp and its Control" which can be downloaded free of charge in PDF format by clicking on the image to the left.
The book looks at how to correctly identify rising damp and goes on to describe a treatment strategy using Dryzone damp-proofing cream.
For best results, the identification of dampness and treatment of rising damp should be carried out by experienced contractors. If you would like details of experienced building preservation companies in your area, please call our technical department on 01403 210204 or visit our technical support page.