Timber comes from trees and is classified as softwood or hardwood. Softwood comes from coniferous trees and hardwood from deciduous trees. Timber has micro and macro structures and can develop defects from conversion, fungi, insects, seasoning or natural forces. There are various wood products created through processes like veneering, plywood production, and impregnation of timber with resins. Proper seasoning and preservation of timber is required to improve its properties and increase durability.

1. Timber and wood products

2. Timber
Timbrian = build
Timber means wood suitable for building /
carpentry / engineering purposes
Standing timber
Rough timber
Converted timber
Timber contained in a living tree
Obtained after felling a tree
Timber sawn & cut into suitable commercial sizes

3. Classification of trees
Exogenous Endogenous
(Grow outwards) (Grow inwards and longer)
Conifers Deciduous
Used for engg
purposes
Eg: - Bamboo, cane,
palm, coconut tree
 Ever green trees
 Leaves do not fall till new
ones grows
 Bears cone shaped fruits
 Eg: Mango tree
Soft wood
 Broad-leaf trees
 Leaves fall in autumn and
new ones appear in spring
 Mostly for engg purposes
 Eg: Teak
Hard wood

4. Soft wood | Hard wood
• Ever green trees
• Distinct annual rings
• Light colour
• Poor fire resistance
• Indistinct medullary rays
• Can split easily
• Light weight
• Broad-leaf trees
• Indistinct annual rings
• Dark colour
• More fire resistance
• Distinct medullary rays
• Can’t split easily
• Heavy weight

5. Structure of a tree
1. Micro structure
2. Macro structure
Timber studied under microscope
Timber studied with naked eye

6. Micro structure
Timber consists of living and dead cells
Living cells – membrane, protoplasm, sap, core
1. Conductive cells
Transfer nutrients from roots to various parts of tree
2. Mechanical cells
Tightly interconnects cells and imparts strength to tree
3. Storage cells
Extra nutrients are stored

7. Macro structure

8. Pith (core/medulla)
Heart wood
Sap wood (Albernum)
 Innermost central portion
 Inner annular rings surrounding pith
 Usually dark in colour
 Used for engineering purposes
 Outer annular rings b/w heart wood and cambium layer
 Light weight and light colour
 It take active part in growth of tree
 Supply nutrients at young age

9. Cambium layer
 Thin layer of sap b/w sap wood
and inner bark
 This get converted into sap wood
Inner bark
 Inner layer covering (protection to) cambium layer
Outer bark (Cortex)
 Outermost protective layer of a tree
Medullary rays
 Thin radial layers extending from pith to cambium layer
 Hold together annual rings of heart wood & sap wood.

10. Defects in timber
Conversion Fungus Natural forces Insects Seasoning
1. Chip mark
2. Diagonal grain
3. Torn grain
4. Wane
1. Blue stain
2. Sap stain
3. Dry rot
4. Wet rot
5. Brown rot
6. White rot
7. Heart rot
1. Burls
2. Callus
3. Chemical stain
4. Coarse grains
5. Dead wood
6. Druxiness
7. Foxiness
8. Knot
9. Rind gall
10.Shake
1. Cup shake
2. Ring shake
3. Heart shake
4. Star shake
5. Radial shake
11.Twisted Fibre
12.Upset or rupture
13.Water stain
14.Wind crack
1. Beetles
2. Marine borers
3. Termites
1. Check
2. Split
3. Cup
4. Bow
5. Twist
6. Warp
7. Collapse
8. Case hardening
9. Radial shake
10.Honey combing
due to

11. 1. Defects due to conversion
Marks/signs placed by chips on finished timber surface
1. Chip mark
May be formed by parts of planing machine, chisel marks, etc
Due to improper sawing of timber
2. Diagonal grain
Affects appearence
Not affects strength
Should cut parallel to layers/fibers
Don’t cross fibers while cutting

12. When heavy equipments falls on a finished surface,
depressions are formed.
3. Torn grain
Due to improper sawing of timber
4. Wane
Not affect strength, but affect appearence

13. 2. Defects due to fungus
Fungus attacks timber if
(i) moisture content > 20 % and
(ii) in presence of air.
Wood submerged in water will not affected by fungus
Wood having moisture content < 20 % will not affected
by fungus

14. 3. Dry rot
Certain fungus attack timber and convert it into powder form
4. Wet rot
Some fungus causes chemical decomposition of wood
that convert timber into greyish brown powder.
1. Blue stain
Sap of wood is stained to bluish colour by action of fungi
2. Sap stain
Sap wood losses its colour due to fungus attack.

15. 5. Brown rot
Rot means decay/disease of timber
Some fungus attacks cellulose  White colour losses.
Thus brown colour of lignin dominates and wood seen
as brown colour.
6. White rot
Some fungus attacks lignin  Brown colour losses.
Thus white colour of cellulose dominates and wood seen
as white colour.

16. 7. Heart rot
Formed when branches are cut
Heart wood is exposed to attacks of atmospheric agents
Tree becomes weak; it gives us hollow sound when
stuck with a hammer.
Fungus develops holes in timber

17. 3. Defects due to natural forces
1. Burls
When tree gets shock/injury in its young age
Also known as excrescences
Due to such injury, growth of tree becomes completely
upset and irregular projections appear on the body of
timber.
2. Callus
Soft tissue or skin which covers the wound of a tree

18. 3. Chemical stain
Wood sometimes discoloured by chemical actions.
4. Coase grain
If a tree grows rapidly, annual rings are widened.
Have less strength
5. Dead wood
Timber obtained from dead standing trees

19. 6. Druxiness
White decayed spots concealed by healthy wood
7. Foxiness
Red or yellow tinge in wood
Due to
(i) Bad ventilation
(ii) Over maturity

20. 8. Knot
Bases of cut-off branches of a tree
Continuity of wood fibre is lost due to knots  Weak
Dark and strong (even saw breaks)
Losses alignment of fibers

21. 9. Rind galls
Rind means bark; gall means abnormal growth
Develops at points from where branches are
improperly cut-off.
Nutrients get still supplied at that points
Fibers gets cutted

22. 10. Shakes
Cracks formed in annual ring direction
a) Cup shakes
Curved cracks
Seperates partly one
annual ring from other

23. Shake
Cup shake
Ring shake
Heart shake
Radial shake
Star shake
10. Shakes
When cup shakes cover entire annual rings
b) Ring shakes

24. 10. Shakes
Cracks formed at centre of cross-section
c) Heart shakes
Extends from pith to sapwood in
direction of medullary rays.
Due to maturity, inside starts shrinking
Divides tree into two or four parts

25. 10. Shakes
Cracks from bark towards sapwood.
d) Star shakes
Cracks upto sap only
Not reach heartwood or pith
Can remove outer area and use
Due to extreme heat or frost

26. 10. Shakes
Similar to star shakes
d) Radial shakes
Outer surface easily dries
Shrinks from outer to inner
But they are fine, irregular and numerous
Extends from bark towards center

27. 11. Twisted fibre
Also known as wandering hearts
Due to twisting of young trees by fast blowing wind
While sawing, it cuts fibers everywhere. Means it cannot
used by cutting. But can use as a single wood.

28. 12. Upset
Also known as rupture
Wood fibers injured by compression
Due to improper felling of trees
13. Water stain
Wood sometimes discolours when it
comes in contact with water
14. Wind cracks
If wood exposed to atmospheric agencies,
its exterior surface shrinks  cracks

29. 4. Defects due to insects
3. Termites
White ants
1. Beetles
Creates holes in wood  for food fine flour like powder
2. Marine borers
Salty waters  make holes in timber for shelter

30. 5. Defects due to seasoning
1. Check
Crack which seperates fibers of wood
Does not extend from one end to other

31. 2. Split
When a crack extends from one end to other

32. 3. Cup
Curvature formed in transverse direction
4. Bow
Curvature formed in direction of length of timber

33. 5. Twist
When a piece of timber get spirally distorted along
its length
6. Warp
When a piece of timber has twisted out of shape

34. 1. Check
2. Split
3. Cup
4. Bow
5. Twist
6. Warp
7. Collapse
8. Case hardening
9. Radial shake
10.Honey combing
7. Collapse
Due to uneven shrinkage, wood sometimes
flattens during drying.
8. Case hardening
Exposed surface of timber dries rapidly
Under Compression
Interior surface not completely dried
Under tension

35. 9. Radial shake
10. Honey combing
Due to stresses developed during drying, various
radial and circular cracks develop in the interior
portion of timber.

36. Seasoning of timber
Newly felled tree contains > 50 % water in form of sap
To use timber for engineering purposes, water should be
removed. (Timber should be dried)
Process of drying of timber to remove water is known as
seasoning.
Water is in the form of sap and moisture

37. Allows timber to burn rapidly, if used as fuel
To improve strength, hardness, stiffness, and
electrical resistance properties
To reduce tendency of timber to crack, shrink and warp.
To make the timber safe from attacks of insects and fungus.
To make the timber fit for uses for engineering purposes
Objects of Seasoning
Improves workability of timber
Reduces much of useless weight of timber

38. Methods of seasoning
Natural Seasoning Artificial Seasoning
When seasoning of timber
is carried out by natural air
or water.

39. Natural Seasoning
1. Water seasoning 2. Air seasoning
Timber is immersed in water
flow which helps to remove
the sap present in the timber
Allow timber to dry for
2 to 4 weeks
Arrange timber logs in layers
in a shed.
Air is circulated freely
between logs  moisture
reduces
Slow process, but we get
well seasoned timber

40. Artificial Seasoning
1. Boiling
Timber allowed to
dry after boiling for
3 to 4 hours
2. Chemical
Timber stored in
salt solution. Salt
absorb water.
3. Kiln
Timber stored in
salt solution. Salt
absorb water.
4. Electrical
timber subjected
to high frequency
AC currents

41. Carried out to increase the life of timber
Preservation of timber
Preserve timber from decaying
To increase durability, to get rid of insects and fungi, etc.
Application of chemical substance on timber surface
Presevatives makes timber ‘poisonous’ for insects and fungi
without affecting the structural properties of timber.

42. Methods of Timber Preservation
Brushing
Spraying
Injecting under pressure
Dipping and stepping
Charring
Hot and cold open tank treatment

43. Types of preservatives for timber
Coal tar – heat and apply using brush
ASCU – powder dissolved in water and apply by spraying
Chemical salts – CuSO4, ZnCl
Oil paints
Solignum paints – applied using brush
Creosote oil

44. Wood products
Industrial timber
– timber prepared scientifically in a factory
– examples are :
Veneer
Plywood
Fibreboard
Impreg timber
Compreg timber

45. 1. Veneer
Thin sheets of wood of superior quality
Thickness = 0.4 mm to 6 mm
Obtained by rotating a log of wood against a
shark knife of rotary cutter
Dried in kilns to remove moisture

46. Process of preparing a sheet of veneer is
known as veneering.
Veneers are used to produce plywood's,
batten boards, and laminboards.
Glued on the surface of inferior wood to
create an impression that whole piece is
made of expensive timber

47. 2. Plywoods
Ply means thin layer
Veneers placed in both longitudinal and transverse
directions  more strength
Suitable adhesives are used to held in position
Available in different commercial sizes

48. Used for:
1. Ceilings
2. Doors
3. Furniture
4. Partitions
5. Paneling walls
6. Formworks of concrete

49. 3. Fiberboard (Pressed/reconstructed wood)
Rigid boards
Thickness = 3 mm to 12 mm
Not able to take loads

50. Used for:
1. Interior decorations
2. Doors
3. Partitions
4. Panel works

51. Impreg and compreg timber

52. 4. Impreg timber
Timber partly/fully covered with resins
Eg: Phenol formaldehyde
Veneers immersed in resins and heated
Trade names: Sunmica, formica, Sungloss
Not affected by moisture, weather, acids, etc
Low contraction and expansion
Glazing appearence

53. 5. Compreg timber
Same as impreg timber, but cured under pressure
Heat + Pressure
More strength and durability – good quality