Rising Damp is the action of water moving vertically through porous building material in contact with the ground. This is brought about by the drying action of air on upper surfaces, which causes the wall to act like a wick. Water will move up the wall by capillary action and evaporate from the surface into the atmosphere.
The height to which the dampness may rise varies accordingly to construction but rarely exceeds 1 meter above ground level.
Water coming from the soil will have dissolved various nitrate, chloride and other salts (called ground salts) and will carry these salts up into the brickwork and plaster.
As the water evaporates over a prolonged period of time an ever increasing amount of these salts will be deposited in the wall.
As these ground salts are easily dissolved they also readily attract moisture from the atmosphere (Hygroscopic Salts). This means that even if the rising damp is cured the plaster may continue to be damp. For this reason the plaster is normally removed when treating rising damp.
Any wall treated for rising damp still has to dry out. The re-plastering specification contains special materials which allow this to take place naturally without the ground salts in the brickwork reaching the surface.
Rising damp suffered by properties with a timber ground floor may also suffer from problems associated with wood rot. A sub floor inspection is strongly recommended.
Penetrating damp in a wall is usually from a source such as wind driven rain, causing moisture to enter the structure in a horizontal direction. Gravity may cause the downward movement of the resultant dampness.
>Whereas rising damp does not occur more than 1.2 metres above ground level, penetrating damp can occur at any level.
Causes of penetrating damp may be from sources difficult to control such as defective brickwork, cracked render, faulty pointing, poor flashings, rainwater goods or from a defect within an adjacent property outside the owner's control.
Penetrating damp can create isolated patches of dampness that increase in size after periods of heavy rain and tend to disappear in long dry spells of weather.
Laterally penetrating damp is a term applied to moisture, which travels horizontally from a source bridging the installed damp course such as high external ground level or earth retaining walls below ground level.
Condensation is a common problem in many properties. Water vapour contained in the warm atmosphere (the humidity) is sealed into the structure as a result of double glazing, draft-proofing, or the sealing up of a disused chimney. When the temperature drops this vapour condenses on colder surfaces such as windows, metal roofing and external walls resulting in damp areas. These are usually in poorly ventilated spaces i.e. corners of rooms, bedroom cupboards and behind furniture.
Human activities such as exercise, breathing, showers, clothes drier use and cooking all contribute significantly to the internal humidity levels of a dwelling.
Moisture from condensation will often attract termites and promote mould growth, it is important to ventilate the interior of buildings to reduce humidity and minimise condensation forming. Often simple alterations to the building can reduce the accumulation of condensation significantly.
The following are terms, which commonly require attention on older buildings to prevent remedial works being necessary.
- Blocked vents- increase cross flow ventilation
- Insufficient vents
- High external ground levels
- Faulty rainwater goods i.e. gutters and downpipes
- The bridging of an existing damp-proof course
- Defective or incorrectly applied external render
- Poor pointing of brickwork
- Defective roofing-flashings
- Defective sealants
- Contaminated plaster
- Incorrect plastering specification
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Last modified: 16 June, 2018
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