Damp proofing is a protective process to ensure moisture cannot pass through the walls of a building to the interior. Damp proofing places a barrier in walls that prevents rising damp problems prevalent in modern homes.
Rising damp is unhealthy, unsightly and can lead to timber decay and heat loss. In addition it carries with it hygroscopic ground salts such as chlorides and nitrates which can absorb moisture from the atmosphere leading to wall dampness in conditions of high relative humidity.
The cyclical nature of the crystallisation and rewetting of these salts can break down internal plaster and ruin internal decorations.
What causes damp?
What appears to be rising damp can be due to various factors – the failure of an existing damp proofing course (dpc), bridging due to the raising of external ground or internal floor levels, or in older buildings, the complete absence of a damp proofing course. Wall dampness may also be due to condensation or an incorrect re-plastering specification.
Other factors such as failed rainwater disposal systems have to be taken into account and it requires a trained and qualified specialist surveyor to make an accurate diagnosis.
What is Condensation?
The air – both that inside our homes and that outside them – contains moisture. The temperature of the air determines how much moisture it can hold, and warm air contains more moisture than cold air. When warm, moist air comes into contact with either a surface or air that is colder than it is, the warm air is unable to retain the same amount of moisture as it did and the water is released either into the cold air or onto the colder surface, causing condensation to form, quickly followed by mould.
Causes and signs of condensation
Air can hold moisture – the warmer the air, the more moisture it can hold. If moist air is cooled by contact with cold surfaces, such as walls, windows or mirrors, the moisture condenses into water droplets (condensation).
Mould often occurs because of condensation. It appears as pinpoint black spots, usually on the side surfaces of external walls, in corners and in poorly ventilated spaces, such as behind cupboards and wardrobes.