Defects in timber

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1. DEFECTS IN TIMBER

2. Defects due to conversion Defects due to fungi Defects due to insects Defects due to natural forces Defects due to seasoning

3. DEFECTS DUE TO CONVERSION Chip mark- indicated by marks or signs placed by chips on the finished surface of timber Diagonal grain- formed due to improper sawing of timber Torn grain- defect is caused when a small depression is formed on the finished surface of timber by falling of a tool or so Wane- denoted by presence of original rounded surface on the manufactured piece of timber

4. DEFECTS DUE TO FUNGI Blue stain- sap of wood is stained to bluish color by the action of certain type of fungi Brown rot- fungi of certain types remove cellulose compounds from wood and hence the wood assumes the brown color Dry rot- fungi of certain types feed on wood and during feeding, they attack on wood and convert it into dry powder form Heart rot- heart wood is exposed to the attack of atmospheric agents; tree becomes weak and it gives out hollow sound when struck with a hammer

5. Sap stain- certain type of fungi feed on cell contents of sap wood; sap wood loses its color Wet rot- some fungi cause chemical decomposition of wood; convert timber into greyish brown powder White rot- certain types of fungi attack lignin of wood; wood assumes appearance of white mass consisting of cellulose compounds

6. DEFECTS DUE TO INSECTS Beetles- form pin holes of about 2mm diameter Marine borers- diameter of the holes made by them is about 25mm Termites/white ants- eat away wood from core of the cross-section

7. DEFECTS DUE TO NATURAL FORCES Chemical stain- wood gets discolored by chemical action caused with it by some external agency Knots- These are bases of branches or limbs which are broken or cut off from tree. The portion from which branch is removed receives nourishment from stem and it ultimately results in the formation of dark hard rings which are known as knots. Shakes- cracks which partly or completely separate the fibres of wood

8. Varieties of Shakes Cup Shakes- curved crack; separates partly one annual ring from the other; develops due to non-uniform growth or excessive bending of growing tree during cyclonic weather. Heart shakes- occur in center of cross- section of tree and extend from pith to sap wood in the direction of medullary rays; occur due to shrinkage of interior part of tree which is approaching maturity Ring shakes- when cup shakes cover the entire ring Star shakes- cracks which extend from bark towards sap wood; usually confined upto the plane of sap wood

9. Twisted fibres - also k/a wandering hearts; caused by twisting of young trees by fast blowing wind; unsuitable for sawing Rind galls- rind means bark, gall means abnormal growth; peculiar curved swellings found on body of tree Upsets- also k/a ruptures; indicate wood fibres which are injured by crushing or compression; caused due to improper felling of tree Burls- also k/a excrescences; irregular projections appear on the body of timber; formed when tree has received shock in its young age

10. DEFECTS DUE TO SEASONING Bow- indicated by curvature formed in direction of length of timber Cup- indicated by curvature formed in transverse direction of timber Case-hardening- exposed surface of timber dries rapidly, therefore shrinks and is under compression; interior surface is under tension Check- crack which separates fibres of wood; does not extend from one end to other

11. Collapse- due to uneven shrinkage, wood sometimes flattens during drying Honey-combing - due to stresses developed during drying, the various radial and circular cracks develop in interior portion of timber; timber assumes the honey-comb texture Radial shakes- are radial, fine, irregular and numerous cracks; run for short distance from bark towards center, then follow direction of annual ring and ultimately run towards pith; occur when tree is exposed to sun for seasoning after being felled down

12. Split- when a check extends from one end to other Twist- when a piece of timber has spirally distorted along its length Warp- when a piece of timber twisted out of shape