DAMP – RISING DAMP

Damp walls and subsequent disfigured wall decorations result from ground water rising within the brick or stone work due to capillary action. An effective damp proof course, providing that it is not bridged, forms an impervious membrane in a wall which physically prevents rising damp. The system most widely used by Building Maintenance Control is chemical injection. This method consists of drilling the walls at calculated centres and then injecting measured quantities of fluid. This emulsifies to form an impervious barrier thus effectively reversing the capillary action which prevents further moisture from rising within the wall.

Rising dampness brings with it ground salts (chlorides, nitrates) that are hygroscopic, i.e. such salts have the ability to attract and retain airborne moisture. It is essential that salt contaminated plaster be removed and replaced strictly in accordance with the Building Maintenance Control Replastering Specification which is specially designed to prevent the migration of salts from the masonry into the new plaster. To avoid the problem of split responsibility Building Maintenance Control offers a comprehensive replastering service.

THE DANGERS OF DAMP

Dampness in buildings can cause a number of problems:

• Any increase in the moisture content of timber above about 20% renders it liable to attack by wood-rotting fungi
• Insulation may be rendered ineffective when it becomes wet
• Plaster and decorations become spoilt and mortar and brickwork deteriorate if they are damp for long periods
• The increase in humidity in the building contributes to condensation problems and increases the risk of unhygienic mould growths and favours the breeding of House Dust Mites.

There are many possible causes of dampness in buildings, including:

• The absence of, or faults in, a damp-proof course at ground level can lead to rising damp
• Defects in the roof, walls or plumbing can allow penetrating damp
• The lifestyle of the building's occupants and the amount of heating and ventilation can influence the development of condensation.

Correct identification is the key to solving dampness problems. This will often involve taking small samples of plaster, mortar and brickwork for analysis on site or at a specialist laboratory.

Dampness - Penetrating Damp

Penetrating damp is most typically caused by rainwater entering the building through broken or missing roof tiles, faulty guttering, cracked brickwork or rendering and rotting or badly fitting window and door frames. A damp patch on an inside wall or ceiling is often an early sign. It may disappear soon after dry weather returns or may persist, especially if large pieces of masonry have been thoroughly soaked. Mould will develop if the dampness persists and, in severe cases, timber may be attacked by wood-rotting fungi. Leaking water supplies or drainage pipes within a building will produce similar symptoms.

Most cases of penetrating damp are easily corrected by making the necessary building or plumbing repairs. However, an exception is where there is lateral water penetration through an earth-retaining wall e.g. in a cellar or basement flat. The water pressure is usually so great that several coats of special waterproofing materials are required to hold the water back. This process is usually called Wall Tanking.