Last week we looked at penetrating damp and how to ensure nothing is blocking weep holes. Another frequent problem is that the damp proof course has failed or that cavities are not performing their function properly.These are problems that are costly to investigate and rectify.
Initial investigation involves removing bricks, on the outer skin, in the area of the damp, and visually inspecting what lies behind. Start by removing a brick adjacent to the weep hole and check that there is a damp proof course, (black plastic should be visible running from the bottom surface of where the brick was removed running diagonally upwards and turned into the joint of the brickwork above, which should be at the same level as your internal floors).
The damp proof course should be supported by a triangular cement fillet behind. If the damp proof course is missing or damaged it can be replaced, but this is a lengthy and expensive process. Often a cheaper solution is to totally weatherproof the outer face of the wall and seal the cavities.
What you are more likely to find is that due to initial bad building, the cavities are blocked by mortar droppings or bits of broken brick that were not removed when the walls were first built. These tend to “bridge” the cavity and allow water to cross into the inner skin and eventually manifest as damp patches internally.
Although it is easier to attend to than a missing damp proof course, I would still recommend the sealing of the outer skin. These are also the usual causes of damp around the tops of windows and at floor or slab level on multi-storey buildings.
Talking about multi storey buildings, beware of buying any unit where there is not a step down on to any balcony or terrace – no step usually equates to damp problems later on, this also applies to ground floor, patios and stoeps.
Of course you may not have cavity walls, in which case water is either penetrating through the brickwork or seeping in around door and window frames.
Water will penetrate cracks that are barely visible to the eye and are often difficult to detect. If you have a damp patch internally, away from door or window frames, scrape down the area externally to look for cracks and test the soundness of the plaster. Tapping with a solid rod will tell you if the plaster is loose or not.
If you find a suspect area apply water under pressure from a hose jet and monitor internally to see if the damp patch becomes wetter.
Next week : Checking door and window frames and sealing outside walls.
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Contact me at don@macalister.co.za or SMS only to 082 446 3859. - Weekend Argus