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
