Describe the common defects of Timber.
Common Defects of Timber Wood
Common defects of timber are as follows.
(i) Knots
(ii) Twist Fibers
(iii) Heart Shake
(iv) Star Shake
(v) Cup and ring Shakes
(vi) Twisting
(vii) Honey Combing
(viii) Rind Galls
(ix) Dead Wood
(x) Druxiness
(i) Knots
Knots are the impressions of broken limbs or branches of a tree and are in the form of hard dark spots. A knot Is either in the root of the branch of the tosses setting in elliptical or concentric direction. The knots known as tight knots arc sound and not objectionable unless very large. Wood with large or loose knots should not be used as such knots are the source of weakness.
(ii) Twist Fibers
The fiber of a tree often get twisted due to the wind action in branches etc.
(iii) Heart Shake
The cavities which extend from the center (heart) towards the outer part (sap wood) are known as heart shake.
(iv) Star Shake
The cavity grows just under the ba1k and extends towards the center it is due to severe frost which bursts the tissues or by severe beat of the sun which burns the tissues.
(v) Cup and ring Shakes
When cracks develop between the adjacent annual rings, it is called cup and ring shake. It Is due to the sap freezing during spring or sudden increase of moisture supplied by the roots.
(vi) Twisting
A spiral distortion along the length of a wooden piece is called Twisting. It is usually the result of improper seasoning.
(vii) Honey Combing
When the drying conditions of wood during seasoning are too severe in the early stage the resulting wood surfers from this defect. The cracks usually occur in the interior of timber.
(viii) Rind Galls
The defect is caused due to the growth of sap wood, over a wound caused by a falling branch. It leaves a cavity where decaying action starts.
(ix) Dead Wood
It is red in color which has less strength and weight. It is caused due to the falling of trees in over-matured state.
(x) Druxiness
It is a defect having decayed spots in timber concealed by healthy wood.
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