Fixing Damp, Rot And Corrosion


Damp m the home is not only ugly, unpleasant and unhealthy. It is also potentially costly, possibly leading to the start and spread of rot which could prove very difficult and expensive to eradicate.

Never, therefore, ignore a damp patch. It may go away in sunny weather, but it will always return with the rain. And its effects could well soon extend far beyond what is immediately visible to the eye.

A damp patch or – worse still – drips or pools of moisture are there for all to see, along with the resulting growth of mould, flaking paint, and peeling paper. But the cause of the damp is usually less obvious. And before you can tackle the problem it is essential that you find out why the damp is there.

Penetrating damp comes into your home via a weakness in the external structure, so check outside for possible defects, including the following: gaps around the doors and windows, porous brick or stonework, leaking gutters or downpipes, defective flashings or cracked or missing roof tiles or slates.

Rising damp is moisture which is coming up through the walls of the house from the soil foundations. Rising damp occurs when there is no damp proof course or if the d.p.c. is faulty.

Plumbing faults may cause damp inside the home. A sudden catastrophe like a burst pipe or cracked cistern is usually immediately obvious and dramatic in its effect. Steady hidden dripping may not be so noticeable; nevertheless, it could be the cause of the damp and then rot over a longish period. Regularly inspect concealed pipework and watch out for seepage from the connection between pipes and waste fittings. Make sure that baths, basins and sinks have the gaps around their edges well filled with a waterproof sealant; the long gap along the edge of the bath is particularly vulnerable.

Condensation should not be confused with either penetrating or rising damp. When you use facilities such as cookers, baths, sinks, etc., they give off large amounts of water vapour which become little drops of water as they hit a cold surface such as a wall or window pane. You can cut down on such condensation by improving ventilation. Consider installing an extractor fan in your kitchen and possibly in your bathroom as well. Less costly and easier to instal are air vents.

Condensation can also be cut back if you improve the insulation of your house, thus eliminating cold surfaces. You could line walls and ceilings with insulating materials such as cork or fire-retard ant polystyrene sheet or tiles or. il you have cavity walls, fill them with plastic foam or dry mineral fibre.

Once you have diagnosed and eliminated the cause of damp in your home, you may still be left with mouldy patches. Wash these over with a solution of one part household bleach to one part water, and leave to dry. Then rinse off with clear water and leave to dry again before scaling the stain with an aluminium or multipurpose primer – this, too, should be allowed to dry out thoroughly before decorating. For treating bad crops of mould, you can buy special fungicides at hardware stores or builders’ merchants.

Various short-term remedies are available for treating damp inside the home. These include water-repellent liquids and damp barrier linings- available at good builders’ merchants. Some can even be applied to walls which are still wet. However, it must be stressed that damp-repellent liquids and linings for the inside of the home are only treating the result of the damp. In the long term it is vital to find and cure the cause of the damp problem.


Rot unfortunately follows on from damp. Indeed, rot is usually the result of damp that was ignored. Rot attacks the wooden parts of your home. The timber affected may be structural such as roof beams or floor joists, and the resulting damage may therefore be tar greater than the simple replacement of the timber itself. Or the timbers may be non-structural such as skirting boards or door frames.

It is important to know that there are two kinds of rot which can attack the timbers in your home: ‘dry rot’ and ‘wet rot’. The names are a little confusing for, in fact, both types of rot thrive on damp, poorly ventilated wood. In time, both break down the timber they have attacked and can destroy it completely. The danger signs, which you can see easily, are warping and cracking in the wood such as skirting boards, and window and door frames. If you suspect that wood has become rotten underneath a coating of paint, stab it with a key or knife, which will sink in easily if the wood is rotting.

Dry rot thrives when the moisture content of wood is around 20 per cent, distinguishing it from wet rot, which prefers a moisture content of around 40 per cent. Dry rot is rightly feared because of the insidious way in which it can spread, by means of minute air-borne spores or through white strands of fungal growth which will travel across brickwork to find fresh timber on which to feed. Dry rot breaks down the wood into cube-shaped sections called ‘cuboid cracking’. You may notice a musty smell, and you will be able to see the growth of fungus quite clearly. A flat orange-yellow pancake shaped fungus, called a ‘fruiting body’ gives out tiny rust-coloured spores. These travel through the air, and some settle on damp wood. Here they start to put out thin white strands which will eventually form themselves into a thick white web of fungus, which in turn will produce a fresh fruiting body, and so on. If you suspect dry rot it is essential to call in a timber specialist immediately. Surveys are usually free and the treatment is guaranteed for 20 or 30 years. Remember that dry rot spreads very quickly once established so act without delay. It is not advisable to attempt treatment yourself.

Wet rot requires wood which is substantially wetter than dry rot: around 40 per cent minimum moisture content. You may well see wet rot, for example, at the bottom of door frames or in window sills. The wood will have a blackened, charred appearance and when it is wet will seem spongy. Wet rot is not nearly so dangerous as dry rot because it does not spread in the same way, but it should be eradicated, First, as always, try to find and cure the cause. Sometimes you can cure wet rot simply by drying out the affected timbers. Otherwise cut away the timber which has been destroyed by the rot and replace with new wood that has first been treated with preservative.


This is another domestic hazard which can cause enormous damage if left unchecked. The most common form of corrosion is rust which occurs when iron and steel are exposed to moisture and air; gradually they change into iron oxide— the powdery red substance we call ‘rust’.

Rust is not only ugly but in time will eat through metals and totally destroy them. Like damp and rot, rust does not go away: it always gets worse, so deal promptly with any traces you find around your home on window frames, radiators and so on. Minor outbreaks should be rubbed away with steel wool, emery paper or with a wire brush, until only bright metal remains. This should be treated at once with a metal primer, because rust can start again within a matter of hours, due to the moisture content of air. When the primer is thoroughly dry, paint to match the surrounding surface.

For very bad outbreaks of rust you can buy special liquid products from hardware stores or motor car accessory shops which, when painted on to rust, convert it into a non-rusting substance which can then be painted over. Carefully follow the directions on the pack, including the safety precautions suggested.

Steel and iron tools will rust unless protected during storage —this particularly applies to garden tools left, say, in a damp shed over winter. Before storing tools thoroughly clean the metal, then coat it with grease to prevent rust. If possible store all metal equipment inside the house in a dry warm cupboard, drawer or box, ideally wrapped in a rust-inhibiting paper.

Non-ferrous metals such as zinc, copper and lead will not rust, but will corrode to some extent. However the corrosion causes oxidization in the form of a protective film which then prevents any further wasting away of the metal.

Electrolytic action

Corrosion is commonly found within plumbing systems due to what is known as ‘electrolytic action’ between two different metals in the same system. The metals involved are usually galvanized steel and copper, for example, you will often find that copper pipes have been connected up to a galvanized steel cold water tank.

If you have a metal cold water tank, inspect its underside regularly and watch out for signs of corrosion which appear as brown and white spots. If you sec these, call your plumber because you may need a new tank. Modern plastic tanks cannot corrode.

It is possible to drain metal cold water tanks and give them two coats of bitumen paint which will protect the metal against corrosion and will not taint the water when the tank is refilled. But if corrosion has already caused the surface of the tank to flake away, all loose particles of rust should be removed before repainting with a rust inhibiting liquid. Rub the loose rust away with wire wool, emery paper, wire brush or, better still, use a wire cup brush attachment fitted into an electric drill, which will be less hard work. If corrosion/rust is well advanced, the only alternative is to replace the tank completely – a job for your plumber.

Metal water tanks, hot or cold, can be protected from corrosion by installing what is known rather strangely as a ‘sacrificial anode’. This is a lump of magnesium connected to the zinc surface of the tank. Electrolytic action then takes place between the anode and the tank. It is not necessary to understand the science behind this ingenious device but it is important to know the result: that it is the anode rather than the tank that gradually wastes away. In other words, the anode sacrifices itself -hence the quaint name. This device will remain effective for around two to three years.

Corrosion builds up in central heating systems because of the electrolytic action between steel radiators and the copper pipes which supply them. The result can be a black iron oxide sludge called ‘magnetite’. As this forms, the metal of the radiators is eaten away, and can eventually disappear completely. The iron oxide sludge can also be the cause of the knocking noises which can build up inside a boiler and pipes. The solution here is to add a corrosion inhibitor to the feed-and-expansion cistern which supplies the water to vour central heatine system.

Various aids are available to remove rust from iron and steel. You can buy rust removers from hardware stores – always follow the instructions to the letter You can also scrape off rust with a wire brush or, even better, use a wire brush cup attachment with your electric drill. Abrasive paper is also useful. As soon as you have removed all traces of rust, protect the clean metal with primer or a film of grease Above: a magnesium ‘sacrificial auttode’ protects metal water tanks from corrosion. 146

Fixing Damp, Rot And Corrosion