Defects in wood can lower its value and affect its strength, working qualities, and appearance. There are three main types of defects: 1. Natural defects that develop in the living tree or after felling, such as knots, reaction wood, compression wood, and grain defects. 2. Seasoning defects caused during drying, including warping, checking, collapse, and honeycombing due to uneven shrinkage. 3. Defects from conversion like chip marks, torn grain, and waney edges from tool marks or bark left on during processing. Proper drying and processing helps control defects for optimal wood quality and performance.

2. DEFECTS IN WOOD
• A defect in wood may be defined as
 Any abnormality or irregularity that lowers its commercial
value by decreasing its strength,
 By affecting adversely it’s working and finishing qualities
or its appearance.
I. Natural deflects
II. Defects due to seasoning , and
III. Defects due to foreign organisms.

3. I. Natural deflects
Natural Defects are described as features developed in the living tree,
or soon after it is felled which may detract from the usefulness of the
timber.
Often it is more economical to remove defects such as dead knots and
replace them with plugs.
Today building up long lengths from shorter glued pieces is becoming
more common.
Building up members by lamination also tends to to more economical
use of timber.

4. 1. Knots
Knots- branches that grew on the young tree that
eventually got embedded within the growing trunk.
The vascular cambium in the branch and the trunk are
one in the same the branch grows continuously along
with the trunk.
Tight knots- during periods of cambial activity, new
wood is added as a continuous layer over branch and
trunk, tightly fixing the knot in the wood of the trunk.
Loose knots- a dead branch that losses its bark and is
not firmly fixed; a knot not held tightly in place by
growth, shape or position.

5. Loose knots
 Three types of loosen knot
1.spike knot or a splay knot- In radially sawn
board it will thus be cut longitudinally
2.round knot - in tangential board it will be cut
more or less transversely, so appearing circular or
elliptical in shape,
3.arise knot - Ina piece of sawn timber of which the
faces are neither truly radial nor tangential, a knot
will lie obliquely through it and may emerge on an
edge.

6. Effect of knotsKnots affect
• checking (cracking) and warping,
• difficulty in working and cleavability of timber.
They are defects which weaken timber and depreciate its
value for structural purposes where strength is an
important consideration.
The weakening effect is much more serious where timber
is subjected to bending and tension than under
compression.
The extent to which knots affect the strength of a beam
depends upon their position, size, number, direction of
fiber, and condition.
However, in some cases, knots increases the aesthetic
value of board/veneer

7.  Reaction Wood It is the specialized type of wood that is produced
on the wide side of such eccentric cross sections
 Reaction wood has different characteristics in softwoods and
hardwoods.
1. Compression Reaction
 In softwoods, it forms mainly toward the underside of the leaning
stem.
 Because the pull of gravity puts the lower side of the leaning
stem in compression
2. Tension reaction
 Tension wood do not easy to detect visually
 In hardwood trees, reaction wood forms mainly on the upper side
of the leaning stem.
 fuzzy surfaces produced during sawing or planing
2. Growth stresses in wood steam

8. 3. COMPRESSION FAILURES
 Compression failures are indicative of
permanent deformation of the walls
of cells which results from
compression of the wood parallel to
the grain beyond its proportional
(elastic) limit.

9.  Is an abnormal condition that causes
the wood to break suddenly and
completely across the grain at stress
levels lower than expected, brought
about by a decrease in cell wall
material.
 It is caused by abnormal per cent of
soft tissues. (Parenchyma Rays)
4. Brashness

10. Grain Defects – these are natural grain features
but are referred to as defects because they cause
working difficulties and affect the overall strength
of the timber. Apart from some growth factors
they are generally caused by the log not being
sawn parallel to the bark.
5. DIRECTION OF THE GRAIN

11.  Spiral Grain – Occurs when fibers have
taken a simple spiral course in the growing
tree as if the tree has twisted.
 Diagonal grain causes the grain of the
wood to intersect the surface at an angle.
 When fibres run at a constant angle or
slope to the axis of the timber
 Interlocking Grain – When fibres of
adjacent layers in the growth ring are
inclined at different angles to the axis.
Boards show ribbon or stripe effect.
TYPES of Grain Defects Spiral GrainDiagonal grain
Interlocking Grain

12. Cross Grain – Caused when fibres have varying
inclination to the edges of the timber.
Wavy Grain – A wavy undulating arrangement
of the fibers
Wane or Waney – The absence of wood on
the edge or corner showing the bark or surface
of the sapwood, (due to improper conversion).
Types of Grain Defects
Wane or Waney
Wavy Grain
Cross Grain

13.  Two types of defects develop in the wood of
living trees, supposedly as the result of freezing
temperatures.
 These are known as frost rings and frost cracks.
Frost Rings. appear to the naked eye as brownish
lines within the boundaries of growth rings which
extend in the same direction and simulate false
rings.
Frost Cracks. develop as radial splits in the bark
and wood near the base of a tree
6. Frost injuries

14.  Number of defects known as pitch, pitch streaks, and pitch pockets
are found in softwoods in which resin canals are normal in the wood,
1.Pitch and Pitch Streaks. These defects develop through the
accumulation of resin to excessive amount, in localized tracts in the
wood; this fills the cell lumina and permeates the cell walls so that
resin-soaked patches or streaks of tissue are present in the wood.
2.Pitch Pockets. when viewed on surfaces at right angle to the grai or
in edge-grain stock, plan convex cavities that are usually wholly
within the boundary of a growth increment
7. Pitch defects

15. Pitch and Pitch Streaks Pitch Pockets

16.  Are small patches of bark imbedded
in wood.
 Bark pockets frequently arise as a
result of bird pecks (work of
sapsuckers, etc.) and from injuries
inflicted on the tree by insects (bark
beetles, etc.).
8. Bark pockets

17. II. Seasoning Defects.
These are defects caused during the drying of the timber. Extreme
care must be taken to control the rate and degree of drying. More
than half the weight of many freshly cut timbers consist of moister
or sap.
Seasoning is simply the drying-out, so that timber is conditioned
(or pre- shrunk) before use.
Seasoning reduces the moister content of the wood to that of the
relative humidity of the atmosphere, i.e. equilibrium moister
content.
Shrinkage is inevitable during drying and efforts are made to control the shrinkage
without undue distortion and splitting.

18.  Checks are ruptures along the grain that develop
during seasoning either because of a difference in
radial and tangential shrinkage or because of uneven
shrinkage of the tissue in adjacent portions of the
wood.
Types of Seasoning Defects
Warp – Any variation of as piece of timber from a flat surface. This
tenancy is caused by the way a piece of timber is cut, the presence of
other defects, and natural stresses in the tree from which the timber is
cut.

19. Types of Warping
A.Bow or Camber – a curvature along the wide surface in
the direction of the length of the board. In floor joists
and bearers this can be eliminated by using blocking
B. Cup – a concave curvature across the face of the board
C. Spring – a curvature along the edge of the board, not
affecting the face.
D.Twist – also known as ‘wind’ is a spiral distortion along
the length of the board caused by twisting of the fibres.
Cupping
Twist
Bow
Spring or Crook

20.  Case hardening The exposed surface of timber dries
very rapidly. It, therefore, shrinks and is under
compression. The interior surface which has not
completely dried is under tension. This defect is known
as case-hardening and is usually occurs in timbers
which are placed at the bottom during seasoning
 Collapse – The flattening or distortion of the cells
showing excessive or uneven shrinkage. It can
sometimes seriously affect the structural soundness of
the timber.
Collapse
Case hardeningTypes of Seasoning Defects

21. Honey combing is the internal splitting in wood that
develops in drying; caused by internal stresses or by
closing of surface checks.
Splits and Checks
Honey combing
Split – A longitudinal crack extending
through the log or timber from one
surface to another, usually at the end of
the piece.
Types of Seasoning Defects

22. III. Defects due to Conversion
During the process of converting loges to lumber, the following
defects may occur
 Chip mark marks or signs placed by chips on the finished surface bf
timber. They may also be formed by the parts of a planning machine.
 Tom grain caused when a small depression is formed on the finished
surface of timber by falling of a tool or so
 Waney Edge Occurs when the bark is left on during conversion

23. Tom grainWane edgeChip mark

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