damp proofing – rising damp solutions

Damp-proof course- rising damp – solutions There is always moisture in the ground, even dining dry spells, and it can find its way up walls like paraffin rising up the wick of an oil lamp unless there is something (such as a damp-proof course) there to stop it. All modern buildings are built with a damp-proof course (dpc). It is near ground level and looks like an especially thick horizontal mortar course, with a thin, usually black line in it, going all the way round the house. In older homes the dpc might be of slate, lead, mastic, asphalt or bituminous felt; pvc is often used in modern buildings. Substitutes for a dpc include chemicals injected into the brickwork, or ceramic tubes drilled into the walls low down at regular intervals.

A damp-proof course that is in good condition should keep rising damp at bay. lf rising damp is evident despite a dpc, one of two things must be wrong. First, something might be creating a bypass to the damp-proof course and introducing damp into the walls above it. The cause might be garden soil piled up against the wall, or a bulk delivery of builders’ sand or coarse aggregate for concrete work. A garden wall meeting the house walls without a damp barrier in between could bridge the dpc, as could a porch or lean-to unless precautions were taken. Some wall claddings tiles or timber and rendering can have the same effect if not applied correctly. The second possible cause is that there may have been a failure in the damp-proof course. Settlement of the structure, for example, can fracture it. If you get rising damp in a home with a dpc, carry out a thorough inspection looking for a likely bridge. Should you find a simple bridge, such as garden soil, get rid of it immediately. A more complex bridge a garden wall, or porch, for example presents greater difficulties. Although a damp-proof course for dealing with such situations can be bought at builders‘ merchants, inserting it once the construction is finished is a major task; you might have to demolish the offending structure – at least in part. If no bridge is apparent, seek expert help, as vetting and repairing a dpc is not work for the do-it-yourselfer.

Inserting a proper damp-proof course in a house that does not have one is a job for trained operators. However, there are several methods of keeping rising damp at bay that can be employed by the practical do-it yourselfer. You can inject into the walls a silicone-based water repellent normally applied to the surface of exterior walls. To do this, bore a series of 16-19 mm holes into the middle of the bricks in two courses immediately above the floor or dpc level. Such large holes might overload an ordinary DIY electric drill, so it might be worth hiring an industrial drill and bit for a day. Slope holes downwards at an angle of about 15° and stop them about 2.0 mm from the other side of the wall (stick a strip of tape round the drill bit as an improvised depth gauge). In solid walls the kind most likely to be affected by rising damp – bore the holes from inside the house. Treat each leaf of a cavity wall separately, boring holes from both inside and out. Bung up each hole with a cork or rubber bung that has a hole in the centre: corks of this type are used in home brewing and can be bought at chemists or home-brew shops. You now need a garden pressure spray fitted with a lance. Fill it with water-repellent liquid and push the end of the lance through the hole in the bung. Operate the spray so that the liquid is forced into the hole. Continue until the liquid comes to the surface of the wall round the hole – it will look as though the wall is sweating – which will take from two to five minutes depending on the porosity of the brickwork. Treat each hole in the same way.

You might be able to hire an electric pressure pump, which would be better than a garden spray, speeding up the work, and forcing the liquid farther into the brickwork. As soon as the treatment is finished fill the holes with a sand-and-cement mortar, and leave for 24 hours. Then brush the area round the holes with more water-repellent liquid. Leave for at least a week before replacing plaster and skirting boards, then redecorate. Another method is to buy an interior damp barrier kit. This does not form a damp-proof course, but provides a barrier that stops damp in the wall from getting through to the inside and damaging the decorations. Normal paint and wallpaper decorations can be applied on top of it. The kit consists of a waterproof laminate, a primer and an adhesive. Remove any wallpaper and loose or flaking paint, and take down the skirting board. Treat the wall with the primer, then fix the laminate in place. A third method is to brush a water repellent made for interior application on to the wall. It will not last as long as the laminate barrier, but will give some protection Rising damp can also rise through solid floors. Treatments carried out on the walls should be continued on to any membrane fitted to a floor.

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