Condensation occurs when warm, moist air comes into contact with a cooler surface and is invariably accompanied by mould growth, which can form on any cold surface, including the contents of cupboards and wardrobes.
Dampness from condensation usually affects the whole area of walls, ceiling and floor, unlike the patchiness of penetrating or rising damp, but can be confined to isolated pockets of cold, stagnant air (behind pictures, wardrobes, etc.)
Much has been written on the subject of condensation, but in many cases the best remedy is natural ventilation with improved heating and thermal insulation. However, the introduction of insulation may cause interstitial condensation unless a vapour barrier is included; this can be difficult in traditional construction.* More information may be obtained from the Wirral Council.
Condensation within a flue, bringing hygroscopic salts and tar to the surface, can cause damp patches on the chimney breast and, in some cases, on larger areas of wall. In mild cases, sealing the wall with aluminium paint, applied once the plaster has dried out, will hold back the stain and permit re-decoration.
Otherwise it may be necessary to strip and re-plaster the chimney breast and line the flue with an impervious lining.
To avoid condensation and damage to chimneys, all flues serving gas fires and gas boilers should be lined with flexible non-ferrous metal liners.
Disused flues should always be ventilated at the top and bottom and the ENTCC can supply information on suitable clay vent terminals for use with Birkenhead Heritage chimneypots.
Portable bottled gas and paraffin heaters produce enormous quantities of water vapour and are not recommended for use in rooms where condensation is likely to be a problem, particularly in basement rooms which are plastered on the hard.