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Aug 01, 2017


There are some disadvantages of wood but they are easy to disregard, and eliminate as long as the cause is known.

Shrinkage and Swelling of Wood:

Wood is a hygroscopic material. This means that it will adsorb surrounding condensable vapors and loses moisture to air below the fiber saturation point.

Deterioration of Wood:

The agents causing the deterioration and destruction of wood fall into two categories: Biotic (biological) and abiotic (non-biological).

Biotic agents include decay and mold fungi, bacteria and insects.

Abiotic agents include sun, wind, water, certain chemicals and fire.

Biotic Deterioration of Wood:

Woods are organic goods. Like any organic good, wood is a nutritional product for some plants and animals. Humans can not digest cellulose and the other fiber ingredients of wood, but some fungi and insects can digest it, and use it as a nutritional product. Insects drill holes and drive lines into wood. Even more dangerously, fungi cause the wood to decay partially and even completely.

Biological deterioration of wood due to attack by decay fungi, woodboring insects and marine borers during its processing and in service has technical and economical importance.


It is necessary to give some short information about fungi agents to take measures against the wood deterioration.

Physiological requirements of wood destroying and wood inhabiting fungi:

A favorable temperature.

The temperature must be 25-30°C for optimum growth of most wood rotting fungi. But some of them can tolerate temperature between 0-45°C.

An adequate supply of oxygen

Oxygen is essential for the growth of fungi. In the absence of oxygen no fungi will grow. It is well known that storage of wood under water will protect them against attacks by fungi.


Generally wood will not be attacked by the common fungi at moisture contents below the fiber saturation point. The fiber saturation point (FSP) for different wood lies between 20 to 35% but 30% is accepted generally.

It is recommended that wood in service must have a moisture content at least 3% less than FSP to provide desirable safety against fungi.


Wood is an organic compound and consists of 50% carbon. That means that wood is a very suitable nutrient for fungi because fungi derive their energy from oxidation of organic compounds. Decay fungi wood rotters can use polysaccharides while stain fungi evidently require simple forms such as soluble carbohydrates, proteins and other substances present in the parenchyma cell of sapwood. Additionally, the presence of nitrogen in wood is necessary for the growth of fungi in wood.


Insects are only second to decay fungi in the economic loss they cause to lumber and wood in service. Insects can be separated into four categories: Termites, powderpost beetles, carpenter ants and marine borers.


There are two types of termites: Subterranean termites damage wood that is untreated, moist, in direct contact with standing water, soil, other sources of moisture.

Dry wood termites attack and inhabit wood that has been dried to moisture contents as low as 5 to 10%. The damage by dry wood termites is less than subterranean termites.

Powderpost beetles

Powderpost beetles attack hardwood and softwood. At risk is well seasoned wood as well as freshly harvested and undried wood.

Carpenter ants

Carpenter ants do not feed on wood. They tunnel through the wood and create shelter. They attact most often wood in ground contact or wood that is intermittently wetted.

Carpenter bees

They cause damage primarly to unpainted wood by creating large tunnel in order to lay eggs.

Marine borers

They attack and can rapidly destroy wood in salt water and brackish water.

Minimizing the Problems of Wood:

Most of the commonly employed strategies for protecting wood involve drying, coating and or impregnation.

Careful selection of wood

Some species have naturally decay resistant heartwood. Such species include sweet chestnut (Castanea sative Mill.), oak (Quercus spp.), juniper (Juniperus spp.). Sapwood is never naturally durable species has little or no decay resistance and must be treated if long-term durability is desired.


Coating provides protection to wood used both indoors and outdoors. Coating prevents rapid uptake and loss of moisture and reduces shrinking and swelling that can lead to surface cracking and other problems. But coating does not totally prevent changes in moisture content. Coating slows, but does not halts moisture level. Coating with solid color or pigmented stains protects wood against ultraviolet rays.

The addition of fungicides to coating provides some protection against development of decay and mold fungi.

Deteriorating paint film actually increases the decay hazard. Cracked paint allows moisture to come into contact with wood surface, and poses a barrier to rapid and complete redrying.


Generally wood will not be attacked by the common fungi at moisture content below the fiber saturation point (FSP). FSP for different wood lie between 20-35%, but 30% is accepted generally: Fungi can not attack wood used indoor and in heated rooms, since the equilibrium moisture content (EMC) is much more below than FSP. e.g. 6%

If wood is soaked in water, wood absorps water and is saturated with it. Finally there will be no more oxygen in wood. In this situation fungi can not grow in them. This is the main reason why woods are kept in water for a while. Besides underwater constructions, it is impossible to use woods completely wet; so when they are used out of water, they have to be completely dried out to EMC in order to protect them against fungi attack. In heated rooms, where the EMC lie between 5-10%, fungi can not survive on them.

One of the most effective ways to prevent degradation of wood is to thoroughly dry it and keep it dry. The last case is very important since even wood that has been klin dried will readily regain moisture if placed in a hamid enviroment.

Wood can be dried in air or in some type of dry klin. Air drying alone is not sufficient for wood items which are used in heated rooms. Therefore klin drying is necessary. Kiln drying has many advantages: One of them is the killing of staining or wood destroying fungi or insects that may be attack the wood and lower its grade.

Wood that will be used indoor need only be dried to provide for long term protection against rot.

Treating With Wood Preservatives

We can prevent decaying of wood by treating it with wood preservatives. But some of the wood preservatives may harm humans and other creatures. For this reason if wood is used outdoor in situations where it is often wet or in close proximitly to liquid water, then wood must be treated with wood preserving chemicals to achieve long term durability.

Wood preservatives are divided into two groups: Waterborne and oilborne chemicals.

About %75 of wood that is commercially treated today is treated with waterborne salts, and CCA is the compound used in treating for the greatest volume of wood.

Only creosote and pentachlorophenel are effective protecting wood in direct ground contact. These are also the only two oilborne preservatives that provide general protection against decay causing fungi, termites, marine borer and other insects.

Oil based or oilborne preservatives are generally used for treating of wood used outdoors in industrial applications; such as ties, piling and poles.

In a serious situation, wood is treated with waterborne preservatives for example chromated copper arsenate and, after thorough seasoning, is retreated with creosote.

Remedial treatment

Wood in service must be periodically retreated by brushing or a variety of other methods.

Retreatment of wood window frames, door frames and wood timber and beams is sometimes carried out by drilling holes in areas where decay has begun and filling these holes with a suitable treating compound. Treating compound in the form of solid rods are mostly preferred since it provides a slow release of active ingredients.

Retreatment of wood used in ground contact must be realized by application of pastes and wrapping with preservative impregnate bandages.

Abiotic Deterioration of wood:


Another disadvantage of wood is that it easily catches fire. Wood consists of organic compounds which are composed mainly of carbon and hydrogen. They can combine with oxygen and burns. Because of these properties, wood is classified as a combustible material.

If the temperature of a inflammable gas is between 225°-260°C, it burns with a touch of flame. After the withdrawal of flame it will stop burning. If the temperature increases to 250°-270°C, it burns with a touch of flame and goes on to burn without a flame. If the temperature increases to 330°-520°C, wood begins to burn spontaneously. Chemical materials, especially extractives in woods structure cause the burning point to change. For example, a resinous piece of pinewood can catch fire in lower temperatures. In addition to this, specific gravity and surface mass (m2/kg) affect the duration of flame. Wood burns harder when the specific gravity and surface mass and moisture content increase, and vice versa.

Using thick wood as a structure element is another way of extension of burning point. Outer surface burns and turns into charcoal. Charcoal, which forms on the surface of wood as it burns is a very effective heat insulator. Therefore large timbers burn very slowly. In addition to this, wood is very good heat insulator too. The outer surface of the wood is 1000°C and the interior part is still 40°C when a piece of thick wood is burning. For this reason, buildings with thick structure elements such as beams and columns do not collapse easily on fire. On the other hand, in steel constructions, as heat increases, steel faces deformation, and their resistance decreases and collapses, where wood is used preventive measures must be taken for safety against fire. In this case wood is not a dangerous material.

Fire Retardants:

It is impossible to make wood noncombustible like inorganic materials. In order to prevent potential dangers, wood can be processed in some fire retardants.

Fire retardants may be divided into two categories: Coating and chemicals-water soluble salts-that are impregnated into the wood structure.

Coatings are used to reduce the formation of volatile, frammable gases by promoting rapid decomposition of the wood surface to charcoal and water. They also protect wood surface against high temperature water soluble salts e.g. diammonium phosphate, ammonium tetraborate, sodium acetat, alkali silicates, borax are used against fire hazards in wood. Wood can be impregnated by these chemicals. This type of process can contribute to the increase of the burning point and retard spread and penetration of flame.

Fire retardants only reduce the flammability of wood and slow or eliminate progressive combustion. They do not prevent burning totaly in the presence of an external source of fire. In this case, wood does not go on burning once an external source of flames is removed.

Prof. Dr. Ramazan ÖZEN 
President, Zonguldak Karaelmas University

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