How to Deal with Damp

If the weather is wet and muggy and damp patches appear on walls and floor then the problem is damp. Damp is caused by such things as broken tiles, defective flashing cracked down pipes and gutters. All these must be fixed immediately or the trouble will spread – it is no use redecorating hoping all will be well – it won’t. Usually the rain which is absorbed by the house walls dries out when the weather is dry. Sometimes, however, the water reaches the interior house walls. This can happen for a number of reasons.

Most modern houses are built with cavity walls, that are an inner and outer wall separated by an air cavity. The two walls are held together with steel ties. Normally there is no way that rainwater can cross the cavity and reach the inside wall (the steel ties are constructed to prevent them forming a ‘bridge’). However, if, during wall construction, mortar is allowed to drop on to the ties a ‘bridge’ will be formed and the rainwater will cross. Painting the outside wall with a silicone water repellent is the answer here. This seals the brickwork against rain but still allows the bricks to breathe so that trapped moisture vapour can escape. Not all solid walls give rise to damp problems but many do. The more exposed walls facing the prevailing winds from the south-west are most likely to be affected. Damp patches in severe cases could extend over an entire internal wall.

Wall Damp How to Deal with Damp

Here again, a coat of silicone water repellent will help. Other safeguards against water penetration are to make sure the pointing between the bricks is in good condition, and any exterior grade decorative paint will also help. Gaps around windows must be sealed. These gaps round a wooden window frame will widen and narrow as the frame expands and contracts in its normal seasonal movement. It is no use filling them with Polyfilla or other cellulose filler; this will crack up and fall out after a short while. Use a mastic compound. This material is fixable and will expand and contract along with the frame, thus keeping the gaps permanently sealed.

If the brickwork of the house walls is porous and the wall ties in the cavity between the inner and outer walls were covered with mortar droppings when the walls were built, then the ties form ‘bridges’ for rainwater to cross to the inside wall. Brush a proprietary damp resisting liquid, usually silicone solution, on to the outside wall. Seal any gaps between door and window frames and brickwork with a proprietary flexible mastic sealer. Do not use cellulose filler as this will crack and eventually fall out due to normal movement of the timber frame.

DAMP-PROOF COURSE

The damp-proof course in the house wall prevents damp rising above the first few brick courses. Take a look at the lower part of the wall’ you should see a horizontal layer of material set into the pointing. This material spans both walls of the cavity and is usually slate or bitumen felt. It continues, unbroken, around all the walls. Normally damp will be stopped when it reaches the damp-proof course. However, should earth be piled up against the wall or path raised to near the damp-proof course level there could be problems. The damp-proof course will be bridged and moisture from the earth will soak into the bricks. In heavy rain, water could splash up about it from the raised path. So keep earth piles away from the house wall and make sure that the damp-proof course is at least 6in. above the level of paths. If you have to, then lower the lever of a path by break it up and re-laying it. Or else apply cement to the house wall to form a skirting. The cement must contain a waterproof agent, but whatever you do, it is worth while applying a water repellent liquid to the wall as well. If the existing damp-proof course is faulty there are several firms who will carry out one of a number of methods of curing the trouble. Their addresses are in the yellow pages directory. You can do the job yourself, though, using a damp repelling liquid – Stroma is one make. There are two grades – one for the inside walls and one for the outside walls. This liquid forms a barrier by penetrating right through the brickwork. In older properties there may not be a damp-proof course at all. In days past, builders often relied on the thickness of material to prevent rising damp – and often it did not work. The firms referred to above will help here, but hey use systems which have to be carried out by specialist.

Rising damp can be caused by earth piled against the house wall over the level of the damp proof course or by a blocked airbrick. If these are not the causes get specialist advices.

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