A-Z of DIY & Building Guides How To Spot And Deal With Damp

Date Published:

27/05/2008

How to Prevent, Monitor & Treat Damp

There are several simple measures that will remedy damp, so it is worth looking over your property thoroughly before instructing an outside firm to carry out expensive work. The problem may be something you can fix quickly with an anti-damp product or a spot of DIY repair. And preventative measures, or spotting early symptoms of damp, will also prove extremely beneficial in keeping your property warm and dry. If the cause of your damp is hard to identify, a damp meter can help you pinpoint the source. They are widely available to buy, but for one-off use, can also be hired from HSS Hire for just £12.50 a day.

Rising Damp

Classic rising damp is usually worse at the bottom of a wall than at the top. Apart from blocked airbricks, the most common cause is 'bridging' - when earth from the garden butts up directly on to the house wall, trapping moisture. This is a common problem, but can be remedied by simply digging away all the soil to see if it makes a difference. If not, you may need to look into installing a damp proof course (DPC) - more on these shortly - or if you have one, it is probably failing to do its job. In old properties, it may prove difficult to install a DPC, so chemical methods - injected into the problem areas - may be the only solution. If the damp is rising through floorboards, a damp-proof membrane may have torn, so it would be best to look into re-fitting.

Penetrating Damp

Penetrating damp forms when water gets in from the outside, so the first step is to check everything in and around the property! Examine gutters, downpipes, flashing, rendering and window frames in detail. Always make sure that downpipes are unobstructed, and if the guttering has seen better days, think about replacing it with new easy-to-fit plastic guttering. Check the rendering to see if it's cracked, plus look at re-sealing any gaps around window frames. Be sure to check underneath window sills as there should be a drip groove to shed rainwater, before it gets to the house wall. If this is blocked with moss, dirt or cement, clear it thoroughly.

An ill-fitted roofing felt on a flat roof will also cause damp. And a cracked wall can let in water, so repair with suitable filler, and fit insulation rubber or weather bars to all door frames. An exterior waterproofing fluid is useful if your exterior brickwork has become porous. This will give it a new water-resistant skin. It only needs to be painted on when the brickwork is completely dry and should also reduce heat loss inside the house (as dry walls give much better insulation than wet ones).

Condensation

Condensation forms when warm air trapped inside the house meets cold walls, and mould quickly spreads. To test, place condensation test strips on the coldest walls - these will change colour if condensation is occurring. A portable humidifier, which will suck up moisture in the air, can help, as will maintaining regular heating, and adequate insulation. Look at DIY film glazing, which can help if windows are the cause. Humidity-controlled extractor fans can be a great help too. To remove mildew caused by condensation, scrub well with a mix of hot water and bleach - leave it to work for several minutes, and then clean off thoroughly.

If you think your property may be damp and you cannot spot an obvious cause, always seek advice from a qualified and reputable surveyor, who will give a truthful evaluation of the problem, without trying to generate unnecessary and costly work. The Royal Institution of Chartered Surveyors can provide a list of approved surveyors in your area.

What is a Damp Proof Course?

Modern homes, built over the last fifty years, normally have cavity walls - two layers of bricks with a space between - and this can help prevent damp. And at the base of the walls, a damp proof course (DPC) is usually installed, which comprises of a waterproof covering, such as slate or a bituminous material. Classic rising damp, where the damp is worse at the bottom of the wall, usually will be remedied by a new DPC.

Damp proof courses are a divisive issue, because they are often costly, and if not property installed and maintained, won't be much use. Not forgetting that rising damp due to a poor damp proof course can cause considerable damage to walls. But even though an inadequate damp proof course can't be fixed, it can be replaced quite easily. Having one installed professionally is advisable, but always try to use a reputable and recommended firm. They should provide you with a damp-proofing certificate once the DPC has been installed, which can be extremely useful should you put the property up for sale.

However if you want to save money and get stuck in yourself, it is actually not that difficult to do. The simplest and most cost-effective method is to use a chemical injection, and all the equipment that is required can be hired. The DIY process involves drilling the necessary holes (around 10mm), and ensuring they are downward sloping to about 150mm below floor level. The holes should be angled, so they slope to the centre of the wall. Holes may be needed on both sides if the wall is especially thick. The brickwork around the holes sweats when there is enough chemical injected into it, and the final and crucial step involves sealing the holes with mortar or plastic plugs. The full kit is available to hire from HSS Hire from £60 for a weekend.