Termites are a highly organized community-building species. Their attack on timber adversely affects the quality and strength of wood. Let us look into the important varieties of termite, how they attack, their characteristics, and also different preventive measures are taken to avoid termite attacks in detail.
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Some insects only attack the living trees and die out when the timber reaches certain moisture content. Holes caused by these insects if not too numerous do not affect the strength properties (ambrosia beetles or pinhole borers). But there are other insects, which destroy the timber after it has been seasoned. One such insect is termite. Termite attacks adversely affect the quality and strength of the timber.
1. Termite
There are more than two thousand varieties of termites whose identification is a complex and skilled task for scientists. The termite, though often called a white ant, is only very distantly related to the ant, although it is a highly organized community-building species. It's two varieties that are of interest in conservation are soil termites and dry wood termites. The former is ground-nesting and the latter a flying variety.
The termite will attack wood, fibres, etc., and destroy almost anything including synthetic material, which is not too hard, repellent or toxic. They have been reported as attacking electrical insulation and plastic water pipes buried underground.
1.1 Why worry about termites?
Termite cause more damages to buildings in India than many other natural disasters. They primarily feed on timber, but also damage paper, books, insulation, and even woody plants. They can destroy the roofing timber of a house within three months of construction.
1.2 How will one know if the building is infected?
The signs of infestation are earthen tubes extending over foundations, walls, timber columns, rafters, beams, etc. The earth tubes are typically about the diameter of a pencil, but sometimes can be thicker.
On many occasions, there will be no visible indication that the building is infected. Termites are cryptic creatures and infestations can go undetected for years, hidden behind walls, floor coverings, insulation, and other obstructions. Termite feeding and damage can even progress undetected in timber that is exposed since the outer surface is usually left intact.
Any treatment on the timber member is ineffective because the chemicals cannot penetrate the enamel paint which has been applied.
1.3 Are all the timbers susceptible to termite attack?
No timber is immune to ground termite attack. Some species of timber such as teak (because of the oil in it), ironwood (messua ferrea), ironwood of Malabar (Hopia Parviflora), etc. have a very good natural resistance against termites. Even very old teak will have good resistance to termites because the inherent oil in the timber would not have evaporated fully. The sapwoods of the above timbers do not have the same resistance to termites.
1.4 Soil Termite
Soil termites are more widespread and they need to maintain contact with the nest in the ground. They can thus be physically barred from the building structure by providing mechanical and chemical barriers during the building process.
The termite shuns light and when forced to take a passage along a lighted area will build a tunnel within which it can travel concealed. It cuts the way through the soft mortar or voids to form the tunnels, which carry it from the ground-based colony to the upper levels where timber is plentiful. Soil termites can pass through a 2 mm crack or an expansion joint (eating through the rubber compound) between adjoining concrete on-ground flooring. Soil termites can also travel under parquetry and floor tiles to get to the wall framing timbers. In the process, they may well find food supplies in small organic particles in the mortar, straw, organic dust, etc.
1.4.1 Characteristics
The sapwood of all and heartwood of most timbers are attacked. The resistance of different timbers varies: exposed to conditions of equal intensity of the attack, one timber may last less than five years another over 100 years.
Exit holes are sometimes present with extruded soil.
The tunnels are made under a thin skin of soil cover.
The attack will continue till the wood is completely destroyed.
White-ants have a well-ordered social system with amazing engineering capabilities and an acute survival instinct; they obtain moisture from the soil and moist decaying timber and communicate using pheromone signals.
Termites avoid light and rarely come out into the open. Often termites are found within timbers where they leave a wafer-thin layer to protect themselves from the outside environment.
1.5 Dry wood Termites
The chemical and mechanical barriers will prevent soil termites from entering the building, but will not prevent attack by dry-wood termites, which are free-flying pests. Infestation by these should be prevented either by using naturally resistant timbers or by pre-treating with timber preservatives.
Dry wood termites cannot digest the cellulose directly. They have other micro-organisms (protozoans and bacteria) in their stomachs that help break down the cellulose which then can be digested by their own metabolism. Dry wood termites do not need a source of water and live off of the water that is produced from the digestion of cellulose.
Dry wood termites are widely found in India and they require fairly high relative humidity. They make their homes within the timber attacked and need no contact with the ground, so in this respect, they are similar to timber–boring beetles. They may fly into the building or be carried therein previously infested timber such as old furniture.
1.5.1 Characteristics
The sapwood of all and heartwood of many timbers are attacked.
Exit holes of 1 to 2 mm diameter are present.
The galleries of various sizes are made inside the wood and the surface will be clean.
They produce fecal pellets, pepper-like in color and appearance, appreciably coarser and granular than that of furniture beetles. The outer skin of the timber is left on the surface of an attacked piece of timber. The feeding termites also push out granular dust through their exit holes. In many cases, the mounds of dust are the only evidence of attack in progress.
The attack will continue till the wood is completely destroyed except for thin skin.
Even painted timber is attacked by dry wood termites which remain entirely above ground with no connection to the soil. Piles of fecal pellets, which are distinctive in appearance, maybe the only clue to their presence.
Dry wood termite live in small social colonies in dry wood. So the process of destruction is much slower when compared with soil termites. Tapping each timber piece with a hammer and finding out the ones which sound hollow is the only way to find out the attack of dry wood termites apart from the granular dust from the exit holes.
2. How to Prevent Termite Attack (Termite Treatment)?
2.1 Mechanical Barriers
One of the mechanical barriers is to provide metal sheets. They are fitted to the top of the foundation. The shields should be made of 26 SWG copper Sheet 0.475 mm thick, which can act as a damp–proof course as well as a termite barrier.
The shield should be made completely continuous around the foundations irrespective of the changes in level. The edge of the shield should extend outwards for 50 mm beyond the top of the wall and should bend downwards at an angle of 45 degrees for another 50 mm. There should be a clearance of at least 20 cm between the shield and the ground on the outside of the foundation wall. All joints in the shield should be double locked and properly sealed by soldering or brazing.
The ground line of the building is the most critical zone to protect timber parts from termites or other timber–destroying insects. Timber always has to be separated from the ground so that neither water nor insects nor fungi have access to it. This can be accomplished by using either concrete or steel or both combined.
Keep untreated wood at least 450 mm above the ground level.
Provide adequate soil drainage. Steps should be undertaken to keep the water away from the building.
2.2 Chemical Barriers
Poisoning the soil creates a barrier for the soil termites. The intent is to establish a continuous, impenetrable chemical barrier. Dieldrin, Aldrin (Aldrex was the brand name), and chlordane (Termex – brand name) marketed under various trade names were the most commonly used. Organochlorines, once commonly used for this purpose, are being phased out.
All timber preservatives are not effective against termites; some are essentially fungicides only and the addition of an effective insecticide to make them suitable for use. This point should be checked before a preservative treatment is specified.
2.2.1 Which termite treatment methods and products are most effective?
In old buildings, chemical treatment is the only solution. Soil-applied liquid insecticides have been around for decades. Their purpose is to provide a long-lasting chemical barrier that excludes termites in the ground from entering buildings. In most cases, termites in the structure die off as well, since they cannot return to the soil. Most former products were repellent rather than lethal to termites foraging in the soil.
Chemical treatments are supposed to control termites for at least five years. The reappearance of the termites within a year or so after the treatment is not because of the degradation of the insecticide, but because termites have found an untreated gap in the chemical barrier.
2.2.2 Will the chemicals harm human beings or pets?
Many of the insecticides are now banned in India. At the same time, some of the chemicals available in India have been banned abroad. Termiticides are tested extensively for adverse effects on health. Dursban (Chlorpyrifos) which was available till recently is not used because the government took it off the market due to cancer concerns in children. The same qualities which made them good insecticides also made them environmentally unsafe.
2.3 Safety precautions to be taken while applying pesticides
Generally, timber preservatives are safer to use if the instructions are carefully followed. But pesticides are extremely toxic and have been made for use by specialists who are aware of the danger and are adequately protected against the hazards.
All pesticides should be handled with care. Always read, understand, and follow the manufacturer’s instructions.
Do not use soil poisons if there are drinking water wells close to or beneath a building. Reliance must be placed instead on mechanical barriers, including the sealing or filling of all joints with mortar. This might not always be possible for all cases.
Care must be taken in applying these liquids, especially in enclosed spaces. Adequate ventilation must be ensured during and after application. Overalls, rubber gloves, and eye shields are essential and face–masks are advisable.
Care must be taken to avoid contamination of water storage tanks by insecticides. Keep animals, children, and unauthorized persons away from the treatment site.
Organic solvents used for some insecticides are inflammable. This may become the cause of fire in areas where such chemicals are stored or used. There is some risk for up to a week while the solvent is evaporating. Smoking should be strictly prohibited and no naked flame should be brought near these chemicals.
Store the chemicals in a cool locked cupboard or storeroom. They should be clearly labeled, stating the name of the chemical and bearing the sign for poison.
Do not permit humans and pets to contact treated surfaces until dry.
As the insecticides can be absorbed through the skin, any contact with the skin should be prevented. If any insecticide comes in contact with the skin accidentally, the affected parts should immediately be washed with soap and water. Eyes affected by splashes should be well washed with water for at least 15 minutes.
Timber that has been impregnated by dipping on the construction site or in the timber yard should not be used before it has dried sufficiently.
Do not use empty chemical drums or plastic bags for any other purpose. They should be safely destroyed and buried.
All operators must wash their hands with soap and water after the use of insecticides particularly before eating, drinking, or smoking. Foodstuffs should never be brought near chemicals.
In case of an accident, medical aid should be called for immediately.
2.4 Why are the applications of chemical barriers in the ground not advisable as a preventive measure?
Most insecticides are highly toxic and expert operators are necessary.
They are expensive.
The treatment is not effective against dry wood termites.
The protection is not permanent and the treatment may have to be repeated after 10 years.
If the treatment is carried out just before the rains, the chemicals may be washed away.
Termites are an important part of the soil ecosystem and can be found all over the world. They can, however, have a negative impact on human welfare by causing damage to uncared timber structures, underground cables, and so on. The annual economic cost of termite damage and prevention is estimated to be in the billions of dollars worldwide. Various preventive methods were discussed along with the important varieties of termite and their characteristics.
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