We’ve all seen it – watermarks, blistering paintwork, peeling wallpaper and a musty smell in the house … sure signs of rising damp. Another common indicator is efflorescence – crystalline formations on an external wall surface.
Rising damp – or ‘salt damp’ as it’s called in some states – can be unhealthy and costly to repair so it’s important to know what you’re dealing with.
It occurs at the base of masonry walls (and sometimes fireplaces and their hearths) where ground moisture is drawn up through the wall. A damp-proof course (a ‘dpc’) will be incorporated within the masonry to block this upward movement of moisture but they can sometimes fail.
A change to the ground conditions at the base of the wall is the most common reason for a building to develop a dampness problem. Raised garden beds or paving are frequently the cause of a dpc breach, particularly if the new surface level is above the level of the dpc. The best dpc in the world won’t work underground!
Blocked sub-floor vents are another problem, preventing natural moisture evaporation around and beneath a building. The minor movement of all structures can also cause brittle dpcs to crack. The slate and mortar dpcs in older brick homes most likely to suffer but tar, sand and mortar dpcs can also fail in this way.
Addressing the underlying problem is the best approach, but where this is ineffective or impossible it may be necessary to repair or replace the damp-proof course completely. There are a variety of ways of doing this with the most common being the insertion of a water-proof membrane or the injection of a silicone-based gel.
In all cases, expertise is everything. Get an independent assessment of the problem first and get at least three quotes from experienced, reputable contractors before you spend money on any repair work.