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Rising Damp |
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Most building materials are porous to
some extent and thus have the capacity to absorb moisture.
When a wall is built in contact with the ground, the
soil, which normally has a high moisture content, will
cause it to become wet. The drying action of the air
on the upper parts of the wall will cause the wall to
act as a wick. Water will move up the wall, mainly in
the mortar by capillarity, and evaporate from the surface.
The presence of nitrate and chloride salts in walls
where rising dampness occurs helps to confirm diagnosis.
In well established rising damp situations, a large
proportion of the dampness in the wall may be there
as a result of these salts. This is described as the
hygroscopic moisture content, as opposed to the capillary
moisture which is directly attributable to the rising
damp from the ground. In addition to increasing the
wall moisture, these salts cause discolouration of decorations
and wallpaper and crumbling and
disintegration of plaster. On brickwork they may accumulate
on surfaces, causing the familiar salt efflorescence
associated with rising damp. Special laboratory procedures
have been developed to ascertain the hygroscopic and
capillary moisture contents of masonry, and these can
prove useful in special circumstances.
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Condensation |
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Air in domestic places will always contain some water
vapour. The amount of vapour in the air at any time
is expressed as humidity
relative to the maximum possible in air at that temperature
(RH). The maximum varies with temperature, as warm air
has a greater water
vapour holding capacity than cold air. If the temperature
of humid air drops, i.e. when the heating is switched
off the temperature may
fall below the dew point temperature for the water vapour
content present, and condensation will occur. This is
particularly prevalent on the coldest surfaces, such
as glass and damp walls and areas where stagnant humid
air can accumulate, i.e. in built-in bedroom cupboards.
This condensation problem is increased if we increase
the amount of water vapour in the atmosphere of our
homes by:-
- breathing
- cooking
- washing clothes
- air drying of clothes
- using paraffin or calor gas heaters, etc.
One method of removing this vapour-laden air from
houses is by ventilation; by keeping windows open
or by having draughts through ill fitting doors and
windows, open fires and chimneys. However, the general
tendency is to seal up these draughts using double
glazing or draught-proofing and sealing up disused
chimneys.
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walls
and plumbing can cause penetrating dampness, and faults
in damp proof courses at ground level can permit rising
damp to occur. The life style of the occupants and the
amount of heating, ventilation and insulation can influence
the development of condensation. Any surveyor carrying
out a diagnosis of causes of dampness in buildings must
be aware of all possible sources of damp and their effects,
so that correct and appropriate remedial measures will
be carried out. 
