What Causes Damp Patches

Damp patches on interior walls can be caused by various factors.  Investigations often
reveal the cause to be a fractured or clogged up gutter.  Downpipes can also crack and leak water into the wall.  As downpipes are often hard up against the wall, it can be difficult to see the problem unless you look closely.  Water seeping through the brickwork of your home over long periods will eventually cause unsightly staining on interior walls.

Plants situated too close to your home can cause problems as moisture gets trapped against the walls.  Even in dry weather, because airflow is restricted by vegetation, walls fail to dry out and dampness soon penetrates.  Rising damp is easily recognised, and is so called because moisture is drawn upwards from the ground into the walls in a capillary action.  It rarely climbs beyond a metre in height.

There are two common causes of rising damp.  Firstly, an impermeable membrane called the damp proof course (DPC) may have been bridged somewhere, allowing moisture to find another route past it.   A patio laid too high above the DPC or a high level flowerbed could also cause this problem.

Alternatively, the DPC may have deteriorated.  In houses where the DPC is made from slate, earth movements can cause cracks, thus allowing moisture to pass through and be drawn up into the walls.  Many old properties are built without any damp proof course at all.

Where a section of DPC has failed, it will be necessary to have it replaced.  Alternatively, chemical fillers can be injected into walls, making them impervious to moisture.  This kind of work is specialised and best carried out by trained contractors who can provide a guaranteed service.

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