6. BARK: outermost layers of stems and roots of
wood plants
CAMBIUM: a cellular plant tissue from which
phloem, xylem, or cork grows by division,
resulting (in woody plants) in secondary
thickening.
SAPWOOD: the soft outer layers of recently
formed wood between the heartwood and the
bark, containing the functioning vascular
tissue.
HEARTWOOD: the dense inner part of a
tree trunk, yielding the hardest timber.
8. TYPES OF TREES:
Trees are classified into two
groups depending upon
growth pattern.
(1) Endogenous trees:
The trees which grow inwards
in longitudinal fibrous mass
are called endogenous trees.
9. (2) Exogenous tress :
The trees which grow in out wards
across horizontal section of stem
are called exogenous trees.
These trees are only fit for
engineering construction.
Exogenous trees are again
subdivided in to two types.
12. SEASONING OF TIMBER:
As fresh timber which is obtained
from trees contains about 30 to 40
% sap or moisture. This sap is very
harmful for the life of a timber.
Therefore, it is necessary to remove
that sap by applying some special
methods. All those methods which
are used for removing the sap from
timber are collectively termed as
seasoning of timber.
13. Advantages of seasoned timber:
It has reduced weight,
It is strong and durable,
It has resistance to decay or rot,
It takes high polish,
It is easier to work,
Its life is more.
14. Types of Timber Seasoning:
The main types of timber seasoning are
as under.
(1)Natural Seasoning,
(2)Artificial Seasoning,
(a) Kiln Seasoning,
(b) Chemical Seasoning,
(c) Electric Seasoning,
(3) Water Seasoning,
15. (1) Natural Seasoning:
In the air seasoning or natural seasoning
or natural drying, seasoning of timber, is
dried by direct action of air, wind and sun.
In this method, the timber logs are
arranged one over the other, keeping some
space or distance between them for air
circulation of fresh air.
Generally this type of seasoning requires
few months to over a year, this is very slow
process.
18. (a) Kiln Seasoning:
In kiln seasoning timber is placed in a
chamber with some special heating
arrangement.
In this process one thing should be
kept in mind that heating system
should be under control, other wise
timber will be crack or wrap. The time
required for this seasoning is 3 to 12
days. This is quick process.
20. (b) Chemical Seasoning:
In chemical seasoning carbon
dioxide, ammonium carbonate or
urea are used as agents for
seasoning, those are applied in dry
state, the inner surface of timber
dries first than outer side.
This ensures uniform seasoning.
The time required for this
seasoning is 30 to 40 days.
21. (c) Electric Seasoning:
In this method electric current
is passed through the timber
logs. The time required for this
seasoning is 05 to 08 hours.
23. (3) Water Seasoning:
In water seasoning, timber logs are
kept immersed whole in the flowing
water. The sap present in timber is
washed away. After that logs are
taken out from water and are kept
in open air, so water present in
timber would be dried by air. The
time required for this type of
seasoning is 2 to 4 weeks.
24. USES OF TIMBER:
Timber is used in:
1.Building construction,
2.Construction of house posts,
3.Construction of beams,
4.Construction of rafters,
5.Construction of bridges,
6.Construction of piles, poles and
railway sleepers,
Continued--------
25. 7. For furniture making,
8. For light packing cases,
9. For high packing cases (for
machinery and similar stores),
10.For manufacturing of agricultural
implements,
11.For making toys, etc,
12.For manufacturing of veneers and
ply woods.
26. DEFECTS IN TIMBER:
Most common defects in timber are:
1. Heart Shakes
2. Star Shakes
3. Cup Shakes
4. Radial Shakes
5. Rind Galls
6. Wind Cracks
7. Knots
8. Dead Wood
27.
28. (1) Heart Shakes:
These are splits occurring in the centre of the
tree and running from the pith (inner most
part) to wards the sap wood from the
medullary (vascular tissues) rays.
In some timbers, these splits are hardly visible
and in some timbers these are quite
permanent.
Heart shakes are caused due to shrinkage of
interior parts due to age. A heart shake
straight across the trunk is not a serious
defect.
30. Medullary Rays:
These are thin horizontal veins
radiating from the pith to wards the
bark. These carry sap from outer side
to inner side.
31.
32. (2) Star Shakes:
These are splits which radiate from
the centre of the timber or from the
bark (outer side), running in the
planes of medullary rays.
These occur due to severe frost or
scorching heat of the sun.
33.
34. (3) Cup Shakes:
These are curved splits which
separate the whole or part of one
annual ring from an other. These
are caused due to the unequal
growth of the timber.
36. (4) Radial Shakes:
These are similar to the star
shakes and occur in timber when
exposed to the sun during
seasoning.
Radial shakes are generally
irregular, fine and numerous.
In this many splits are appeared.
46. DETERIORATION OF TIMBER
(OR)
DECAY OF TIMBER:
There are so many agencies which
may cause decay of timber. But there
are three main harmful agencies
which cause timber decay.
47. (1) Decay or Rot:
Decay or rot of timber is the result of
the activity of various bacterias and
fungi, which utilize various portions
of timber as food; they require both
oxygen and excess moisture. Hence
timber having moisture content
below 25 % will not rot easily.
48. 2) Insects:
There are so many insects which attack the wood,
out of them termites (white ants) are the main
insects which are very dangerous for timber.
Termites of one class live under ground and eat
wood and forms tubes or tunnels inside it.
(3) Fire:
Fire is also the damaging factor for timber. As
timber has tendency to burn, so fire can
damage it easily.
49. PRESERVATION OF TIMBER
• Process of protecting or preserving the timber
structures from the attack of destroying
agencies such as moisture, dry-rot, internal
decay, fungi, insects etc
• The basic principle employed is to poison the
food of fungi in the form of preservatives.
50. TIMBER PRESERVATIVES:
The following are the types of
preservatives commonly used
• oil preservatives like
pentachlorophenol, creosote oil, oil
paints, coal tar etc
•Commonly employed for outdoor and
wet exposure conditions. Offer painting
difficulties
51. (1)Oily substances insoluble
in water:
Coal tar oil is the best known and
widely used preservative material of this
class. It is obtained during the
destructive distillation of bituminous
coal. It is available in many grades and
types. It has high degree of penetration.
It has highly toxic effect to wood
destroying fungi.
52. (2) Water soluble preservatives
• Zinc chloride, boric acid, sodium fluoride etc
• commonly adopted for interior wood work since
they are washed away by rain water.
•They are colorless, odorless, and involve very
little fire hazard. Timber treated with such
preservatives can be painted and varnished
easily.
53. METHODS OF APPLYING PRESERVATION
A. Pressure process or Vacuum Process : the
preservative is injected under pressure into the
timber. Most effective method of treating timbers.
•Sub divided into two types:
Fuel Cell or Bethel Process
Empty cell or Repairing Process
54. B. Soaking Treatment:
Timber is submerged in the preservative solution
for long time until the required absorption is
obtained.
C. Surface Application:
• Brushing: hot oil preservative solution is applied
liberally in several coats on timber surface by good
quality brushes.
•Spraying: solution of preservative is filled in a
spraying pistol and then applied on the surface.
55. • Dipping Method: timber to be treated is soaked or
dipped for a short period in preservative soln. this
gives better penetration to brushing and spraying.
Depth of penetration depends on the type of timber
D. Hot and Cold Process: timber is stacked in the tank
and cold preservative usually creosote is run into
tank till timber is completely submerged. Heated to
85 to 95 C. process is repeated . Air in timber first
expands and then contracts which creates partial
vacuum. Sucks preservative into timber. For treating
sapwood andheartwood
56. ASSIGNMENT
What are the different wood based
products obtained?
• Hardboards
• Plywood
• Fiberboards
• Veneers
• Particle boards or Chip boards
