Damp Proofing Course – DPC -A Guide

Damp Proof Course DPC – An Installation Guide

The purpose of installing a damp proof course in a property is to provide a barrier to moisture. The bricks and blocks that are used to build the walls of a house are often quite porous, and when the natural moisture from the ground moves up into a wall through capillary action it is known as rising damp. This can happen when the barrier between the moisture and the wall fails, or it may be that no damp proof membrane was installed in the first place, which was often the case with older properties. If one was used it would often be accomplished by using stone or slate as a damp proof material. In order to comply with current building regulations a membrane consisting of a thin trip of plastic or a roll of bitumen might be used, and in some cases a course of non-porous engineering bricks might be installed before the brickwork is continued.

lack of cavity tray and no weep holes allowing bricks to become saturated

lack of cavity tray and no weep holes allowing bricks to become saturated

Damage cause by damp

The damage that damp can cause may vary from cracks through to destroying the bond between the render and brickwork along with the paintwork. The rising moisture can also bring with it ground salts, including nitrates and chlorides. These salts can also absorb moisture from the atmosphere which will lead to high humidity due to the dampness in the walls. If there are timbers such as floor joists or stud walls that are in contact with, or built into the walls then these will be in danger of rotting if the problem is not addressed. The first signs that damp is penetrating the walls may be damaged skirting boards and floor boards, or maybe crumbling and salt stained plaster, followed by peeling paint or wallpaper. Rising damp often leads a tide mark along a wall as it moves upward. One other thing you will notice is a musty smell in the room that remains even when windows are opened.

Work can be done to prevent damp issues.

Work can be done to prevent damp issues.

How to treat rising damp

Chemical Injection dpc

Chemical Injection dpc

Rising damp is best dealt with by injecting special chemical fluids into the wall. These silicon based fluids work by lining the pores along a length of wall and the resin neutralises the charge attraction of the walls pores to water molecules. The resin needs to be injected into the mortar joints as this layer can act as a damp proofing layer. It is normally placed a minimum of 150mm above ground level and close to the solid floor internally or below the floor joists.

Damp that is penetrating through the walls may require silicon water repellents or bitumen coatings on the exterior surface to protect the structure. The symptoms of penetrating damp show themselves through damp patches on the floors, walls or ceiling. These patches may also darken when it rains. It is also a good idea to check rainwater downpipes and guttering for leaks as these would need to be repaired before any work is carried out.

Here is an example of a DPM.

Here is an example of a DPM.

Once the walls have dried out it will be necessary to remedy any damage that has occurred such as using a pre-mixed render on the internal walls after stripping of the old plaster. Any damaged timbers would also need to be replaced and surrounding timber treated to prevent any further deterioration.

rising damp will effect internal plaster and decoration

rising damp will effect internal plaster and decoration

Conclusion

It is important to have damp proof work carried out by a specialist as the work will carry a certification for the property.

 

Image credit: Image credit: Bryn Pinzgauer and Tim in Sydney