damp proof course - bridged

Damp proofing describes the control methods used to prevent rising damp in walls of buildings. Given a basic understanding of cause and cure, rising damp can be prevented by professional or DIY damp proofing, whereby a remedial damp proof course is installed using damp proofing cream designed for the professional builder and those competent in DIY or by the insertion of an electro osmosis damp proof course.

Rising damp is a form of dampness caused by the movement of ground water through a permeable masonry wall having no effective damp proof course by which to stop damp from rising. The water rises through the pores in the masonry via a process called capillarity.

Capillarity is an electrochemical action which attracts water molecules to mineral surfaces, enabling water to move vertically through pores of a certain size despite the counteractive force of gravity. The same process is responsible for the movement of moisture from tree roots to tree tops via intricately stacked hollow cells. Fortunately the pores in masonry are not as fine as those in trees and rising damp in walls rarely ascends more than about one metre in height.

Rising damp only becomes a problem if it affects vulnerable materials or finishes that are in contact with the damp wall. For example if it affects timbers such as joists, skirting boards or the bottom of door frames such as to provide wood rotting potential or if it causes wall plaster or wall coverings to deteriorate or become stained. Damp proofing products and techniques are designed.to stop capillary action and prevent damp in walls.

The Problem
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Effective professional or DIY damp proofing requires a chemical damp proof course injection in accordance with BS6576:2005. The remedial damp proof course should be sited along the base of a wall at a level that is at least 150mm above external ground level and internally beneath ground floor joists, or close to the floor if solid.

Suitable chemical damp proofing cream treatments are tested and approved in the UK for injection into the mortar bed course. The mortar presents the only continuous passage ascending up a wall through which water is able to rise. Therefore a mortar bed joint is the only layer that can function as a damp proofing layer. Introducing a chemical DPC into just each brick or block unit along a stretch of wall will not stop dampness rising through the joints between.

Contrary to common belief a silicone damp proof course does not form an impervious physical barrier. Chemical damp proofing is an effective method of lining the pores along a stretch of masonry wall with a silicone resin water repellent. For the purists, silicone rising damp treatments work by neutralising the charge attraction of the masonry pores to water molecules.

An essential requirement of BS6576: 1985 Code of practice for installation of chemical damp proof courses is to replace wall plaster that has been contaminated by the ground salts deposited by rising damp. Best practice, though not always the most convenient, is to leave the plaster above the new damp proof course on the wall for several months following the damp proofing injection. This allows the salts to surface during the drying out process and the extent of plaster replacement to be properly ascertained

Given the pore-lining characteristics of chemical damp proofing treatments, it goes without saying that they are only suitable for use as a damp proof course where mortar joints are continuous throughout the depth of the wall. For thick or random stone walls with a rubble fill, consider the use of an active electro osmotic damp proofing system.  This system relies on positioning positively charged anodes (+) along the wall and a cathode (-) at a lower level in the ground. Using the process of osmosis, free water molecules are repelled from the anodes and attracted to the cathode, thus reversing the  capillary action of rising damp.


Ultracure DPC injection cream

The 21st century has brought us modern damp proof cream technology. Damp-Cure DIY damp proofing kits contain a high strength cream formulation, which has been independently assessed and accredited by the British Board of Agrement (BBA Certificate 13/5023). Holes are drilled into the mortar at 100-120mm intervals and the damp proof cream is injected to fill each hole. The DPC cream comprises a blend of silicone and a silicone carrier.

Early DPC creams were made using thickening agents to stiffen the cream and prevent it running out of the host drill hole. Tests indicate these early creams work well in dry walls that are subsequently subjected to wet conditions.  Modern Damp-Cure injection creams are formulated without thickening agents, being stiffened instead by emulsification to form a 100% actve damp proof treatment that migrates well along the host mortar bed course in damp wall conditions.

There is no no need to call a self proclaimed specialist, you can buy professional DPC cream online in a specialilist DPC injection kit or in damp course builder packs or in easy to use DIY damp proofing kits, saving hundreds of pounds in the process.  Alternatively, for thick rubble filled stone walls take a look at an electro-osmosis damp proof kit.

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