Woodworm and Dry Rot

CERTAIN timbers such as teak or cedar are practically immune from insect attack and possess high resistance to decay. Others have little natural resistance to insects or deterioration, due to exposure to varying weather conditions. Some have a high degree of durability if constantly submerged in water; this is true, for example, of elm, which will withstand prolonged immersion without deterioration, but it is apt to decay if left overlong in the ground.

The circumstances in which timber diseases and insect attack occur largely depend on the quality and type of timber, the uses, correct or incorrect, to which it is put, the degree of dampness, and the natural characteristics of durability for a specific type of timber. These factors cannot be described in greater detail in this entry; but, for the handyman, the following general information may be regarded as a good general guide in the prevention and cure of timber diseases and insect attack.

Wood is subject to two main forms of deterioration, attack by the larvae of certain small beetles and rotting by the parasitic activities of fungoid growths which, stimulated by damp conditions, attack and consume substances in the wood tissues, notably starch.


There are several species of beetles whose sole purpose in life appears to be the selection of timber on which to lay their eggs. These eggs later develop into larvae or grubs which burrow into the wood and obtain, simultaneously, natural protection and a source of food. The extensive tunnelling of the grubs progressively undermines the structural strength of the timber, which, if subjected to a constant load, will eventually collapse. The grubs of wood-attacking insects may be found in living or dead trees, seasoned and unseasoned timber, fences, furniture, structural timber, and even in timber submerged in water.

Although each species possesses special characteristics and preferences (the pin-hole borer beetle and not the larvae, for example, being responsible for the excavation of the tunnels), the method of attack and nature of damage are very much the same for all the species. There are, also, variations in the lapse of time necessary to the completion of the life cycle for one species or another. The three species in most common distribution throughout the British Isles are the death-watch beetle, the powder-post beetle and the furniture beetle. There are others such as the longhorn beetle and the pin-hole borer, but it is proposed to deal only with the effects and treatment of insect attack in general.

Although the powder-post beetle is responsible for an immense amount of damage, principally in timber yards, the furniture beetle is no doubt most often encountered by man since the field of its existence is closely associated with domestic wood fittings and furniture. It is the grub of this beetle therefore which has earned the term woodworm, generally applied when wood is found to have been attacked by burrowing insects. The furniture beetle, approximately 3/16-in. Long, will select, by the peculiar mechanisms of its instinct for survival, crevices in joints and obscure corners of rough unpolished or untreated wood surfaces, I.e. the undersides of tables, the unexposed surfaces of cupboards, etc. in which to deposit its eggs.

The presence of the grubs may be detected (if not by the very small entrances to the tunnels) by the fine dust, called frass, which may be discovered on the carpet or floor, particularly if the furniture has remained undisturbed for a reasonably long period.

The tunnels excavated by the grubs of the furniture beetle are about -yin. In diameter and follow random directions, frequently intersecting until the whole body of the wood is affected. As previously mentioned, some timbers are more liable to attack than others. Honduras mahogany ismore prone to insect attack than cedar, which contains an oil that discourages the presence of wood beetles. Birch does not possess a high resistance to insect attack. Sapwood is more often attacked than sound mature timber. In general, wood with large grain pores and sapwood suffer most. The furniture beetle, however, will attack most softwoods and hardwoods, sapwood and heartwood. The death-watch beetle, notorious for its destruction of heavy timber in ancient buildings, shows a decided preference for wood containing sections of sapwood and an. Attack, as has been proved by recent research, is often preceded by the onset of dry rot fungus indicating the partiality of the death-watch beetle for damp, unhealthy wood in the early stages of decay. The powder-post beetle-infests wood with its larvae, which will consume and reduce the interior of a piece of timber to a friable mass while leaving the outcr surfaces more or less intact.

There is only one sound remedy for timber which is severely affected by insect attack, particularly if the component is designed to support a constant load, as with rafters, beams, joists, floorboards, etc.;. remove it and replace with new sound timber, preferably treated with a preservative. The quick conversion and discarding of affected wood is a general practice., among other precautions and preventive measures, in timber yards. This is not always possible with pieces of furniture, but certain practical methods for halting damage and exterminating larvae may be adopted by the handyman, although it is emphasized that there is, as yet, no ideal remedy.

Preservatives in the coal tar group (creosote, solignum, etc.), useful for spraying external woodwork or roof timbers, joists, floorboards, etc. are good deterrents and, if impregnation of the wood is successful, will often kill off the grubs. Repeated spraying -is advocated for affected wood. As a preventive measure against infection of other sound timbers, spraying in the spring and autumn is a good practice. Furniture and internal domestic fittings should not generally be sprayed with coal tar group preservatives as the odour is somewhat objectionable. Turpentine, or paraffin mixed with a fluid antiseptic, sprayed liberally over the affected surfaces, which should be presented face upwards, if possible, so as to allow infiltration of the fluid into the tunnels, will give good restilts. This work should be effected in conditions ensuring good ventilation. Rub wax polish liberally over the affected surfaces to seal the tunnel entrances. Similarly, fill the crevices and gaps between joints with wax. If it is an antiseptic wax polish so much the better. Small wooden boxes or ornamental objects may be completely immersed in turps so as to ensure efficient saturation and flooding of the tunnels. It should be remembered that paraffin and turpentine are solvents of paint and should not be used when it is imperative to preserve a painted surface intact. There are also many effective insecticides on the market and it is generally possible to select one that is suitable, for the job. The use of water-soluble salts, in trade use, for the elimination of grubs is not recommended to the handyman as they are mostly of a poisonous nature and require a special technique in application. Fumigation, likewise, is a specialized process employing noxious chemicals, giving off poisonous vapours. Very low oven heat may, of course, be employed on wood, unlikely to be damaged in the process, to kill off the grubs. Recent research in insecticides suggests that more effective methods may be made available for the elimination of wood- attacking beetles, but it is not improbable that impregnation of seasoned timber with such preservatives, by the open tank immersion or pressure impregnation methods, before distribution from the timber yards to the manufacturer, will be the most effective means of preventing the onset of these pests.

Dry Rot

More common than attack by insect is the rotting of wood tissues caused by the activities of organisms in the parasitic growth of fungus. The fungoid growths commonly seen on living and dead trees and on seasoned and unseasoned timbers are actually the fruits or flowers of the parasitic organism which attacks the wood. These organisms, called hyphae, microscopic in size and fibrous in shape, will only be found in damp humid conditions or where the timber is heavily saturated with moisture. The hyphae penetrate into the wood, from which they extract food and assist the generation of spores in the fungoid growth, finally reducing the wood to a soft friable mass. Most timbers are subject to .dry rot if the surrounding atmosphere is humid or where moisture in the wood becomes stagnant by long standing in unventilated conditions. The hyphae w,ill also explore every surface of wood in the vicinity and will traverse brickwork, metal and other surfaces in search for more material to attack. Hyphae actually penetrate mortar and brick in their persistent efforts to extend the field of damage. The best preventive measure against the infection of wood is to ensure good ventilation, freedom from saturation by moisture and the liberal use of a deterrent in the form of an approved preservative, many of which are available from builders’ merchants and ironmongers, etc.

In the house, the handyman is advised to inspect all the sources of ventilation and to look for any evidence of dampness in timber and wall surfaces. It should be noted that perforated bricks or metal plates are installed in the outer walls of the house to give free ventilation to such timber as floorboards, joists, and other internal structural timbers. These bricks or ventilation points must always be free and uncovered and any evidence of dampness should be investigated. Where these air bricks do not exist it is permissible to make a limited removal of solid bricks at the position where damp occurs; but this measure is not generally advised unless there is evidence to prove inadequate ventilation. Metal gratings should be fitted in place of the bricks. Walls which have ceased to be entirely weatherproof can be responsible for the onset of dry rot in timber by creating damp or humid conditions, the moisture tending to filter downwards and into timber. Damp timbers in leaky roofs and patches of flooring such as those beneath sinks, baths, and basins are specially subject to this defect, and suitable commonscnse measures should be adopted to prevent the saturation of the wood. In regard to repair of walls, roofs, and floorboards reference should be made to the appropriate sections in this website.

The treatment of contaminated timber is simple. Eliminate the cause of dampness, the only condition in which dry rot can exist, and ensure good ventilation. Any infected timber or loose materials should be burned. Such timber as may be affected should be scraped and cleaned thoroughly. The use of a blow lamp on the defective surface is advised wherever this method can be utilized without injurious results; a slight charring or roasting of the surface, no more than would be necessary, say, for the removal of paint, being sufficient. Afterwards, spraying or painting with an approved preservative will give additional immunity. A good solution is 2 parts of zinc chloride to 100 parts water. Another solution, also brush applied, is a mixture of 2 oz. Of corrosive sublimate to every pint of water. Be thorough in examina- tion of all timber adjacent to the visible area of infection. External timbers may be treated with creosote, or other coal tar group paints. Even timber that looks sound may be in the early stages of infection sb it is a wise precaution to apply a preservative to this timber by spraying or brushing. Apart from the ordinary use of oil paints, a hot solution of five parts boiled linseed oil to one of coal tar, brushed on, is a good sealing agent against damage to external timbers. Any timber badly damaged by dry rot, particularly if it bears structural weight, should be removed and new sound timber fitted. This measure, however, requires careful discretion and the advice of an expert should be obtained before making any major repairs.

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