Damp is a silent demon that can wreak havoc on your home, often manifesting itself in dark emanations and evil smells but also capable of carrying out dastardly deeds without you suspecting a thing. Once spotted, you must find the source before embarking on a programme of treatment and prevention involving a combination of good ventilation, heat, damp-proof courses and good maintenance.
Poor ventilation is one of the commonest causes of damp. Buildings need to "breathe" and rely on constant air circulation. Anything that impedes the flow of air through your home prevents moisture from escaping or evaporating and leads to damp.
Houses also breathe through the porous materials used for walls, floors and roofs, so coating exterior and interior surfaces with impermeable layers (eg, certain types of plaster, paint and water-resistant coating as well as external render, pebbledash and cladding) can increase the risk. Anxious not to lose expensively produced heat, many people turn their homes into hermetically sealed boxes with little or no ventilation. As well as being bad for your health, this can create huge damp problems, so make sure there is always some provision for air circulation.
Signs include steamed-up windows and puddles on the window sill, damp patches, peeling wallpaper, black spotty mildew, water running down walls. While badly ventilated bathrooms and kitchens are at obvious risk, less obvious forms of condensation occur in unseen places such as chimneys where a blocked-in fireplace has no vent, and underneath tightly fitted laminated flooring which prevents air circulation and can lead to damp floor timbers which in turn can develop dry rot.
Recommended treatment: A combination of good ventilation and heating. Sometimes opening a window is enough but installing vents and extractor fans, especially in bathrooms and kitchens, will help. Avoid the use of non-porous paints and wallcoverings. In severe cases, a dehumidifier may help.
The presence of rising damp is not always obvious as much of it happens below floor level, but as it gets worse it will start to creep up walls. Look out for patches above skirting boards and use your nose - you can often smell damp even if you can't actually see it. If left unchecked, rising damp can cause damage to brick, concrete and wood structures, and cause wet rot and the dreaded dry rot.
Moisture from the ground beneath is normally repelled by a damp-proof course in the foundations or an impermeable layer such as plastic sheeting which is laid underneath concrete floors and new floor coverings. With old solid floors, the concrete substrate or grouting may have started to break down, letting moisture through.
Recommended treatment: If no damp-proof course exists, many people go for a chemical damp-proof course which is injected into the walls to prevent moisture rising above a certain level. This treatment involves the structure of a property, and so is subject to regulations. Installation should only be carried out by a reputable and reliable company which will provide the necessary guarantee that will have to be produced when selling your home or making an insurance claim.
Typical signs are damp and blotchy patches on the wall, wet and crumbly plaster, the presence of fungus or mildew and, in severe cases, water on the surface. Penetrating damp comes from a variety of sources including loose or missing roof tiles, leaking downpipes, overflowing gutters, faulty roofs and wall flashing and badly fitting windows or doors. Pointing, cladding, external render and damaged pebbledash will also allow moisture to penetrate. On the ground floor, damp problems arise if the ground level outside is higher than the damp-proof course or covers the air bricks designed to allow air to circulate underneath suspended floors.
Recommended treatment: Keep your home well maintained and in good repair inside and out. Check roofs regularly by looking in the roof space for any wet timbers or signs of water coming in. Make sure that pointing and exterior coatings are sound and properly applied. Keep areas around damp-proof courses and air bricks clear. Where a general air of dampness prevails (eg, in cellars and basements or in properties which get little direct sunlight), a radiator or storage heater left permanently on a low setting will help to keep the atmosphere drier.
Obvious leaks are soon spotted and dealt with, but slow and very small leaks can, over time, grow into big damp problems. Look for growing patches on floors, walls or ceilings and drips and puddles where they shouldn't be. Watch out for damaged or badly installed pipework and appliances (especially dishwashers and washing machines), bad tiling, porous grout and perished rubber pipework. Damaged or poor seals around showers and especially over baths are common culprits (see panel), and the damage often goes unnoticed until it appears down the walls or on the ceiling of the room below.
Recommended treatment: Vigilance. Be on the lookout for any problems, check connections and waste pipes on domestic appliances regularly. Make sure that seals around baths are effective, and always use a registered plumber to carry out any work. It is especially important to check regularly for leaks if you live in an upstairs flat as the person who suffers will be your downstairs neighbour!
Repairing a water-stained ceiling
A water leak from a downpipe in the roof will cause dark staining (mildew) in the ceiling, as well as lots of; nasty, fungal-like growths. When wood gets wet, mildew seeps through and will continue to show as a dark stain, even through multiple coats of regular emulsion.
1. Make sure the root cause of your water leak is fixed (it's always best to get an expert in to advise on such matters). Allow the affected area to dry out thoroughly, ensuring it is well ventilated.
2. Cover the whole area in dust sheets, and put on your safety specs to avoid getting an eyeful of dust and detritus. Now gently scrape off all the "growths" with a paint scraper, then carefully sand down the whole area of ceiling.
3. Now apply a couple of coats of stain block in paint-on or handy aerosol form - this is a special (admittedly not very eco-friendly) substance that will give your ceiling an impermeable layer of protection against the staining mildew. Fast-drying versions of stain block dry in as little as 10 minutes. Once the second coat is dry, apply a final coat of regular emulsion paint and, with any luck, you'll be able to say adios to those ugly stains for good.
The joining edge between your sink or bath and the bottom of the backsplash should be protected with a flexible silicone sealant. It's a good idea to renew this occasionally to stop water seaping through into the wall behind.
Squeezing from one end of the backsplash to the other, apply a continuous line of sealant, keeping a steady pressure (and hand!). If your line looks irregular at any point, smooth it down with a wet soapy finger, taking care not to remove any of the sealant from the surface in the process.