Rising damp is a seasonal effect. Increasing in winter with after tables rising, but falling down in the summer. Best described as dampness, resulting from water in the ground. Rising up through masonry, by capillary flow.
Caused by faulty rainwater goods, faulty plumbing, dampness associated with flues, lateral penetration of groundwater or condensation, resulting from water vapour in the air.
Rising damp must be distinguished from rain penetration through the structure (penetrating damp).
1) A supply of water or saturated soil at the base of the wall.
2) A pore or tube structure in the masonry comprising the wall.
3) Absence of a barrier (damp course), to upward movement of moisture.
Salts – Water from the soil contains low concentrations of soluble salts.
Evaporation – Restricted in its heights by evaporation, which is taking place continuously. From liquid surfaces in contact with unsaturated air.
Surface coatings – Bitumen paint etc which block evaporation will result in an increase in the height to which rising damp rises
Water table – It is dependant upon a supply of water being available at the base of a wall.
Damp patches or tide markings ruin interior decoration. Can create unhealthy living conditions. Increased heat losses. Hygroscopic salts cause staining and retain moisture in the walls. Weakening of the fabric or structure of the building, providing conditions suitable for fungal growth, causing degeneration of timber.
Hygroscopic Salts (particularly chlorides/nitrates) – Are normally present in walls and plaster suffering from rising damp. These salts often concentrate in a band in the upper area of dampness. And may cause electrical (conducting) moisture meters to give spurious readings.
Because of high remedial costs it is essential that the diagnosis is as positive as possible to distinguish between other sources of dampness, by a Qualified Surveyor.
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