As per Indian Standards (IS: 4021–1967), it is preferred that timber used for building construction purposes is of one of the following four types:
- Hardwood like teakwood for permanent structures.
- Softwood like deodar wood for permanent structures.
- Hardwood like sal wood other than teakwood for permanent structures.
- Softwood other than deodar wood used for any temporary structures.
Classification of Teak
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.
Classification of Deodar
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. The wood should be free of sapwood.
2. Second-class Deodar
No individual ‘hard and sound knot’ shall be more than 40 mm in diameter. The total area of all the knots in the piece should not exceed 1.5% of the area of the piece. The wood should be free from sapwood. However, traces of sapwood are allowed.
Classification of Other Woods
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.
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