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.