Timber is a type of wood which has been processed into beams and planks. It is also known as “lumber” in US and Canada. Basically, timber or Lumber is a wood or firewood of growing trees. Any wood capable of yielding a minimum dimensional size can be termed as a timber or lumber. It is a stage in the process of wood production. Timbers are used for the structural purpose. Those woods which are adapted for building purposes are timbers. Finished timber is supplied in standard sizes for the industry. Timber is used for building houses and making furniture.
There is high demand for timber as a building material. From building construction to furniture making, timbers have numerous uses. These uses have made timber an important building material.
Properties of Timber
The quality of timber must be ensured before using it for a purpose. The quality can be ensured by investigating the properties of timber. Here we have discussed both physical and mechanical properties of timber which affects timber quality.
Followings are the physical and mechanical properties of timber:
- Specific Gravity
- Moisture Content
- Shrinkage and Swelling
- Free of abrasion
While selecting timbers for use, one must check these properties to ensure the quality. At the same time, it is also essential to ensure that the timber is defectless. To learn more about timber defects read: Defects in Timber | Defect Types & Causes
These properties are briefly discussed below:
Color is a uniform property by which most trees are characterized as they show variation from tree to tree. Light color indicates weak timber. For example, freshly cut teak, Deodar, and Walnut have a golden yellow, whitish and dark brown shades respectively.
Smell is a good property as timbers for few plants as they can be identified by their characteristic aroma. Fresh cut timbers have a good smell. For example resinous smell from pine.
For the resistance of any kind of damage, hardness is an obvious property.
Variation of timber in specific gravity (0.3-0.9) is found. It depends on pores present inside timber. The specific gravity of this light material is less than that of water (<1). But in case of compact wood where pores are almost absent and become heavier, their specific gravity increases up to 1.5.
Timbers are hygroscopic and gain water from nature (atmosphere). The absorption of water or dehydration depends on atmospheric humidity. If timbers moisture content is high that means the timber quality is low. Water content is the risk of fungal attack.
Several types of grain arrangement found. On the grain structure quality of timber varies. Grains remain closely related.
- Straight grain: Arrangement of vascular tissue (xylem and phloem) is important which grow parallel to the length of the timber that is termed as straight grain.
- Coarse grain: vascular tissue and fibre arranged broadly and widely.
- Interlocked grain: Instead of parallel arrangement twisted, a spiral arrangement may be found.
Shrinkage and Swelling
The percentage of shrinkage and swelling varies from plant to plant. Some give higher percentage after drying. Shrinkage starts when cell walls of timber start to release water. In moisture atmosphere timber swells when cell walls absorb water. Good quality timbers swell less. Timbers having thicker wall swell more than a thinner one.
Best quality timbers have the highest strength. Strength means capable to bear loads. Anisotropic material like timber has different structure at the different portion. So, the strength of timber is different at different points. Grain structure determines the strength of the timber. Some types of strength are
- Compressive strength: 500 kg/cm2 to 700 kg/cm2 load is enough to test timbers strength.
- Tensile strength: When timber is enough strong to the tensile force. If perpendicular force is made then timber is weaker. 500-2000 kg/cm2 is the range of tensile strength load.
- Transverse strength: Enough bending strength indicates good quality timber.
Timber having higher density have a thicker wall. An important property that quality of timber. Moisture content: Presence of defects: There may be some of the natural and artificial defects in timber such as cross-grain, knots, and shakes, etc. All of them cause a decrease in the strength of the timber.
Timber has to have the capability to bear shocks, jerk. Anti-bending and ant splitting characteristic is needed. Old timbers have annual rings which indicate their age is a good indicator.
Another property elasticity means timber should attain its own shape after use. Because of this quality, it is used in sports bat.
Environmental change with season can’t effect good quality timber.
A good quality timber has the property to resist the attack the infection of fungus or other insects. This resistance quality makes timber better.
This property is gained if the timber is from a sound tree. A defectless tree is free from sap, shakes, and dead knots. To know more about timber defects read: Defects in Timber
A good timber is always easy to work on it. Easy to drag using saw on good timber. The finishing can be done well.
A good quality timber gives good sound.
The texture of good timber is fine and even.
Free of Abrasion
Timber should not be damaged by the external environment. It has to gain the ability to protect its skin.