Defects in timber (1)

DEFECTS IN TIMBER

Defects due to insects

Defects due to seasoning

DEFECTS DUE TO INSECTS

Insects that are responsible for the decay of timber:

Beetles

Marine borers

Termites

BEETLES: These are small insects and they cause rapid decay of timber. They form pin-holes of size about 2mm diameter in wood. They attack the sap wood of all species of hard

woods. The tunnels are formed in all directions in sap

wood by the larvae of these beetles. The timber is converted into fine flour like

powder. They usually do not disturb the outer shell of

timber.

MARINE BORERS : These are generally found in salty water.they actually make holes in the wood for shelter. The diameter and length of the hole may go as high as 25mm and 60mm respectively.

The wood attacked by marine borers gradually loses its colour and strength.

TERMITES: These are popularly known as the white ants.

They make tunnels inside the timber in different directions and usually do not disturb the outer

shell.

Very few timbers such as teak and sal can resist the attack of these termites.

Such timbers have certain chemicals in their composition and the smell of these chemicals is not favourable for the termites.

DEFECTS DUE TO SEASONING

Bow Case-hardening Check Collapse Cup Split Honey combing Radial shakes

Twist Wrap

BOW: This defect is indicated by the

curvature formed in the direction of length of timber.

CASE-HARDENING: The exposed surface of timber

dries rapidly. It therefore shrinks and is under compression. The interior surface which has not dried completely is under tension. This defect is know as the case-hardening.

CHECK: A check is a crack that

separates fibres of wood. It does not extend from one end to the other.

SPLIT: When a check extends from one

end to the other, it is known as a split. COLLAPSE: Due to uneven shrinkage, the

wood sometimes flattens during drying and this is known as collapse

CUP: This defect is indicated by the

curvature formed in the transverse direction of timber.

HONEY-COMBING: Due to stresses developed during

drying, the various radial and circular cracks develop in the interior portion of timber. The timber thus assumes the honey-comb texture and the defect so developed is known as honey-combing.

RADIAL SHAKES: These are radial

cracks. TWIST: When a piece of timber has

spirally distorted along its length, it is known as a twist.

WARP: When a piece of timber has

twisted out of shape, it is said to have warped.