DAMPNESS IN BUILDINGS

Dampness is one of the main causes of deterioration in buildings. Dampness is also the chief cause of decay affecting timber structures in buildings. It is dampness, coupled with frost, which breaks down brick and stone surfaces. Dampness affects the cost of heating building, the deterioration of interior decorations and the health of the occupants.

There are three basic causes of dampness in buildings:

RISING DAMP - Dampness rising up walls from the ground due to either the total lack of damp-proof course, or to the breakdown of an existing damp-proof course.
PENETRATING DAMP - Dampness due to the lateral penetration through the surface of the brick or stone because of the porous nature of the material used, OR water penetration from another source above ground level.
CONDENSATION - Dampness generally caused by warm humid air inside a building condensing on the hard, cold, sealed surfaces of the walls.

rising Damp

Stone or brick, with which most buildings in the country are built, together with the materials used to bond one brick or stone to its neighbour, contain numerous tubes or pores (generally referred to as capillaries). Due to various physical phenomena, it is possible for water to travel up these tubes, and the narrower these tubes are the higher the water will travel. To overcome this, in the more modern type of buildings, a damp proof membrane is inserted just above ground level. These membranes have been of slate, lead, copper, bituminous felt and more recently, polythene. These break the continuity of the capillary action and prevent the water rising up through the wall. Rising damp discolours decorations, causes wallpaper to peel off, paint to blister and flake and moulds to grow. These problems are often exaggerated by salts 'efflorescing' on the surface. If these salts are 'deliquescent' they will attract moisture from the air and make matters worse.

Apart from the disfiguration and deterioration which rising damp causes and the recurrent costs which result, a damp house is a cold house and, therefore, an expensive household to heat. Rising damp is very conducive to dry rot which can spread over a considerable area and prove expensive to rectify.

penetrating damp

Penetrating damp is the ingress of water above the ground level, however it arises. Special care is necessary when investigating damp problems, particularly where the building has solid external walls, to differentiate between rising damp and penetrating damp. Penetrating damp may not just be the result of porous stone, brick or mortar, but may equally be attributable to faulty or blocked roof gutters, downpipes, flashings or flaunchings around chimneys and gable walls, faulty hip or valley flashings or tiles, missing slates or tiles, the absence of caulking or sealing around door and window openings and the absence of drip grooves below the window sills, etc.

condensation

In some instances the results of condensation can appear as rising damp, particularly where the plaster and the rendering are taken down and connect with a solid floor in kitchens, ground floor bathrooms, pantries, storerooms, etc. This, generally, is the result of warm humid air from the interior of the building condensing as it comes into contact with the hard cold surface of the walls.

Condensation also results in black mould growth on the wallpaper and other finishes and this mould is difficult to eradicate.

It is important to ensure adequate ventilation, particularly in areas of high humidity, eg. Kitchen and bathroom. In extreme cases it may be necessary to install an electric dehumidifier to remove moisture from the air over an extended period in order to prevent the growth of mould.

hygroscopic salts

Whilst hygroscopic salts are not strictly speaking the cause of damp problems in building, they are the unpleasant result of these problems. Although the cause of dampness may eventually be cured, the hygroscopic salts will persist unless they themselves are treated as a separate problem. These salts can be introduced into the building by the building materials employed in construction, but more often as a result of rising dampness. The salts are carried up the wall and deposited in the wall. When an effective damp proof membrane is inserted by chemical injection, moisture is prevented from rising and that already in the wall commences to evaporate. In so doing, it carries various salts to the surface and these salts are left in the surface material after the water has evaporated. They tend to become more and more concentrated on the surface. The rising concentration of salts increases the surface tension of the water and moisture is attracted to the affected areas.

POINTS TO NOTE

After the insertion of a damp proof course, water in the masonry can only disperse by evaporation. The time taken for the process to become complete is dependant on a number of factors, eg. temperature and humidity (although a 'rule of thumb' is one month per 25mm of wall thickness). It is essential that no decorative finish is applied that will prevent evaporation. Wallpaper will inevitably peel and mould and mildew growth will appear, particularly if the property is left unheated for a period of time. Our own specification and products for replastering prevent residual hygroscopic salts within the masonry from migrating to the surface. This specification must be strictly adhered to in order to obtain a dry surface.
Important: The insertion of a damp proof course DOES NOT dry out already damp walls, it only prevents further vertical ingress of ground water. A damp proof DOES NOT prevent condensation. A damp proof course DOES NOT prevent damp due to porous masonry resulting in the ingress of moisture during rainfall, etc, or in the event of masonry being built below ground levels. Poor pointing and cracked renderings contribute to this problem.