Author: Haroon Khalil

Another important quality required for timber is it should to be durable. It should have a long life. It should be capable of resisting the actions of fungi, insects, chemicals, physical agencies and mechanical agencies during its lifespan.

This is the property of a material which returns to its original shape when the load causing the deformation is removed. Timber should possess this property, as it is essential when timber is used for bows, carriage shafts, etc.

It should possess a uniform structure. This is ensured when there is firm adhesion of fibres and compact medullary rays. Further, the annual rings should be regular and closely located.

As timber is a bad conductor of heat, it should be dense enough so that it resists fire. A good timber should not contain resins and other inflammable oils since they accelerate the action of fire.

The timber should be hard so that it is in a position to offer resistance when it is being penetrated by another body. As such hardness is imparted to the wood by chemicals present in the heartwood and the density of wood.

The timber should be strong enough to effectively act as structural members, such as joists, beams, rafters, etc. Further, it should be in a position to sustain loads applied gradually or suddenly to it. Preferably, the strength should be adequate in direct and transverse directions.

Characteristics of good timber are given below in the order of decreasing significance:

Sal, another hardwood, grown in the sub-Himalayan regions and in Madhya Pradesh, is heavier than teak, which has to meet the requirements of first-class deodar. Timbers of Mango, Benteak, etc., are categorized as second-class.

Only teak has been divided into three classes, whereas others are classified into two classes only, viz., first class and second class. 1. First-class Deodar No individual ‘hard and sound knot’ shall be more than 25 mm in diameter. The total area of live knots shall not exceed 1% of the area of the piece.…

Teakwood is classified into three grades, viz., superior, first and second depending on the defects. The classification of teak based on the permissible defects, viz., cross grain, knots, pith, pockets or streaks, sapwood, pin holes and worm holes is presented in Table 10.1. Table 10.1 Permissible defects for the classification of teak Source: IS: 4021–1967.