How to treat and prevent woodworm attacks

Start by looking for signs of frass on and under floorboards and joists, skirting boards , cupboards—particularly those under stairs—and furniture. Pay particular attention to any timbers which may be damp, such as those under sinks and baths, in cellars, garages and garden sheds. A common site of infestation is roofing timbers, so make sure you check the joists and rafters in and around the roof space.

Frass looks like white wood dust and is made up of tiny pellets of wood, chewed and excreted by the larva. Where these tell-tale piles of wood dust are discovered, closer examination should reveal circular, perfectly formed flight holes with clean wood inside. If you find flight holes with dull, weathered wood inside and there are no signs of frass nearby, the attack is probably not active.

Treating furniture

Woodworm in furniture should never be neglected, as it can easily spread from here to the structural timbers of the house. Old-fashioned remedies such as wiping furniture with turpentine, although reasonably effective in the short term, do not give lasting protection.

Effective woodworm-killing fluids which consist of an insecticide in a light and penetrating solvent are now readily available in the UK. These should deal permanently with all stages of the woodworm life cycle in one thorough treatment. Bear in mind, though, that it is not sufficient to treat just those areas where flight holes are visible, for grubs may be tunnelling anywhere in an infested item.

Certain woods used in cabinet making, such as Cuban mahogany excess fluid from the surface with a dry cloth and fill the flight holes with wood filler. If you decide to repaint furniture, mix a proprietary insecticide powder with the undercoat to discourage further activity.

Treating skirting boards

Woodworm is particularly fond of the back parts of skirtings, so if a skirting board is attacked you must remove it for treatment.

Carefully remove the damaged skirting board from its fixing on the wall then strip the paint from its surfaces with a proprietary paint stripper or a blowlamp to leave it clean and smooth. Brush woodworm fluid liberally on to all the surfaces, paying particular attention to the end grain.

Leave the timber for a few days, then wipe unabsorbed fluid from the surfaces, refix the wood and paint it.

Structural timbers

If you find evidence of woodworm attacks in structural timbers such as roof rafters or floor joists, treatment should be thorough: prolonged infestation can seriously weaken the stability of a house.

But before you treat these timbers you must first establish the extent of and teak, are immune from woodworm attack. Beech is thought to become susceptible only after about 40 years and oak after about 60 years, so all secondhand or old furniture should be inspected very carefully for signs of infestation. Pine and plywoods, on the other hand, are susceptible to attack at anytime.

As a precaution against woodworm in furniture which has not already been attacked, it is well worth using a proprietary insecticide polish; these give protection against infestation as well as producing a good, deep shine. But bear in mind that you will have to apply the polish to unpolished surfaces—such as the back and underside of a chest of drawers—as well as to the visible ones, to give the furniture full protection.

To treat an affected piece of furniture, begin by cleaning it to remove any dust and dirt, then remove any drawers and shelves. Woodworm fluid does not penetrate paint, so if painted furniture has been attacked, it is best to strip all the paintwork from the item with a stripping compound before treating the wood. Before you start to apply woodworm fluid, remove any carpets or upholstery in contact with the furniture, as the chemicals can eat into such materials. If a piece of furniture has to be stood on a carpet within two weeks of treating, lay some protective cloth under the legs.

When the wood is clean and dry, use a paint brush to coat all the surfaces with fluid. If the furniture is polished, make sure that the fluid is suitable as some types can cause damage to polished surfaces. Coat the insides of drawers and the back and underside of the piece of furniture, as well as the visible surfaces. Pay particular attention to the bottoms of chair and table legs, which are usually left roughly cut.

This initial surface treatment should penetrate the wood to a depth of about 3mm. To kill larvae deeper in the wood, follow this by an injection treatment. There are several types of proprietary injectors available for this purpose. They consist of either an aerosol with a plastic tube attached to the outlet, or a soft plastic squeezable bottle with a nozzle fitted. Use the injector to pump fluid into the flight holes, following the manufacturer’s instructions, so that it is forced along all the galleries formed by the larvae.

When you have treated all surfaces and flight holes, leave the article for a few days to let the wood absorb the fluid thoroughly. Then wipe off any the damage by making a probe into the wood with a bradawl. Where damage is severe, the affected part of the wood should be cut out and replaced with wood pre-treated with preservative.

Any cuts or holes you need to make in the course of fixing new timbers must also be treated. If severe damage is spread over a large area, removing the wood may pose a threat to the structure of the building, so you should call in expert help. If the damage is less severe, the timbers should be given a thorough insecticide treatment.

Painting structural timbers with woodworm fluid, as for furniture might not eradicate all the pests or provide enough protection. For this reason, low-pressure spraying equipment, which can be hired or bought from builders’ merchants, has to be used. High-pressure point sprays are not suitable.

For small areas, a simple garden spray-lance, about 600mm long with a hand-pump attachment will do. Over large areas hand-pumping can be tiring, so a pressure-operated unit is preferable. The nozzle should be set to produce droplets rather than a fine spray.

If you are dealing with timbers over a wide area, such as in the roof, you will need plenty of woodworm fluid. Two 25 litre drums should be sufficient for an average-sized roof, but if the timber is particularly dry it will soak up more fluid. In the UK, fluid is obtainable from builders’ merchants.

Safety precautions

Woodworm fluids are often toxic and the solvents can attack the skin, as well as materials such as rubber and polystyrene. Therefore, it is essential to wear protective clothing and gloves when operating spraying equipment.

To avoid inhaling the solvent in the confined space of a roof, wear an industrial light fume mask, available from some chemists and builders’ merchants. Wear goggles designed for working with chemicals to protect the eyes, and rub a barrier cream over any exposed skin, especially around the face and wrists.

If your electric cables are of the old rubber-insulated type, these too must be protected. Cover any exposed cables of this type with sheets of polythene or, better still, paint them with a wood sealer. Protect any junction boxes with polythene or mastic putty.

If you are working in the roof space, remove any loft insulation and do not replace it until evaporation of the fluid is complete: this can take up to a week in a confined area. Cover open-topped cold water storage tanks as well, and keep them covered for one month after spraying.

As most of the solvents used are flammable, on no account smoke or use the spray near a naked flame; nor let any flame come into contact with the area until evaporation is complete. Turn off the electricity in the area and leave it off for at least 24 hours after spraying—if you need light to work by, hire a fume-resistant fireproof light unit such as those used by garage mechanics.

Finally, make sure that the area is as well ventilated as possible during spraying, and afterwards as well to help the fluid to evaporate.

Spraying the timber

If you are using spraying equipment in the roof space, it is dangerous to work while balancing on the joists. Lay down planks across the joists, to give yourself easy access to all the areas and a platform on which to place your equipment. Before spraying, clean down all the timbers with a stiff yardbroom and a small, stiff handbrush then collect the debris with a heavy-duty, preferably indus- trial, vacuum cleaner. Where timbers are seriously weakened at the edges, scrape off the decayed wood to a maximum depth of 12mm then vacuum away the remaining debris.

When the area is clear you can start to spray, following the manufacturer’s instructions and taking care to direct the spray only at the timbers. Spray the liquid evenly over the timber surface, gradually building it up until it runs.

Use the lance to reach into inaccessible areas such as the apex and eaves of the roof. As you spray, the fine ‘fall out’ of fluid will be sufficient to protect really awkward corners.

If you have woodworm in floorboards or joists, take up every fourth or fifth board so that you can reach between the floor joists and the undersides of the boards. When you have sprayed this area, replace the boards and spray the top surface. Leave plenty of time before you replace carpets or linoleum and follow the manufacturer’s advice on how you can best protect your floor coverings from the fluid.

Should you accidentally stain the plaster with fluid while spraying timbers, leave it for a week or two and if the stain still shows, coat it with an aluminium primer before redecorating.

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