Persistent dampness can cause considerable damage to a property if it’s allowed to penetrate into the fabric of the building unchecked. The building regulations therefore have a number of stipulations that must be fulfilled whenever a new building is being erected, or repairs or modifications are being made to an existing property.
The following is concerned primarily with the measures that should be undertaken to protect the building from the effects of rising and penetrating damp.
Rising damp is caused by a natural phenomenon called ‘capillary action’ wherein ground water is drawn vertically upwards through fine pores in masonry and brick walls, rather like a wick.
To prevent this from occurring, a horizontal waterproof damp-proof course (DPC) should be inserted into the walls at a height of no less than 150mm (6in) above any adjacent ground level. This height ensures that the DPC is unlikely to be ‘bridged’ by some other material that allows water to flow around it, and that splashing rainwater does not bounce above it.
In addition, a vertical damp-proof course (DPC) or damp-proof membrane (DPM) should be inserted between walls that are protected from damp at the bottom, but are abutted by other walls that are not protected.
Widespread use of damp-proofing methods did not begin until the 1950s, so it is entirely possible that older properties are not protected at all.
There are several types of damp-proof course, as described below:
Being liquid, a chemical damp-proof course is a far more practical and less invasive solution than inserting a solid DPC.
This involves injecting a silicone-based liquid into the wall at the suitable height to create a water-repelling layer.
However, the effectiveness of a liquid damp-proof course can vary since it does not pass through the wall evenly, and can create continuous holes through which moisture can still pass. In addition, the solvents in the liquid which enable the chemical to dry off quickly do not mix with water well, and can therefore fail to pass through the very wettest parts of the wall.
Modern technology does provide us with an alternative, in the form of a cream chemical damp-proof course, which is water-miscible and slow-curing to ensure that the DPC passes through as much of the wall as possible.
Note that a liquid damp-proof course will not work in walls constructed of breeze block, as these are not porous and do not permit the liquid to flow through them at all.
To install a chemical damp proof course, you will require the following tools
Top tips for installation are as follows
A traditional DPC is made of a layer of solid, waterproof material such as bituminous felt, copper sheet or polythene. Solid DPCs are considered to be the most reliable method of resisting groundwater ingress, but they are difficult to add to a wall after it has been built since grinding out the mortar coarse can weaken the wall and risks cutting through pipes and wiring. Therefore, this approach to damp-proofing is best left for when a wall is being built from scratch.
A DPC layer should be placed between courses of brick 150mm (6in) above ground level in both the exterior and interior leaves of cavity walls.
Small porous clay tubes may be inserted into rows of closely spaced holes in the mortar 150mm (6in) above ground level, where they increase the rate of evaporation and therefore limit the amount of moisture that can rise above them. Although a simple and inexpensive approach, this is the least reliable of the damp-proofing methods.
When an electric charge is applied across a body that contains moisture, the water molecules are drawn to the negative electrode. This law of science is used in damp-proofing wherein titanium electrodes are inserted into the wall, with the negative cathode at the bottom so that the natural tendency of water to rise up through the wall is counteracted and reversed, so the water simply returns harmlessly back into the ground.
The electrodes and the wires that connect them are hidden beneath the mortar that lies between the relevant courses of brickwork, and are connected to a power unit, which plugs into a standard 13amp socket, and maintains the very tiny electric charge across the masonry, and of course the whole system must also be earthed.
Modern homes tend not to have suspended wooden floors, but solid concrete ones instead since they are cheaper to construct. Like any other masonry, concrete will allow damp to rise through it unless a waterproof barrier is placed in its path.
This is where a damp-proof membrane (DPM) is put into use; essentially a large sheet of polythene, bituminous felt or copper sheet which should be placed between the concrete slab and the screed on top of it.
This membrane should be linked up to the DPC that is placed in the interior leaf of the surrounding cavity wall, to ensure that the concrete floor does not bridge the DPC in the wall.
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