TIMBER

Definition
The term WOOD is used to refer to the substance that makes up the TREE.

It is the hard, fibrous structural tissue that is commonly found in the stems and roots
of trees. The primary function of wood is to support the tree, enabling it to grow
straight and tall enough to be able to absorb sunlight for photosynthesis. Wood also
enables the transfer of water and nutrients to growing tissues and leaves.

The term TIMBER is used to refer to the WOOD at any stage after the tree has been
felled. This can include the raw material, also known as rough timber or the
processed material.

The word timber is derived from an old English word timbrian which means to build.
The timber thus denotes wood which is suitable for building or carpentry or various
other engineering purposes.
WOOD TIMBER
The following three terms are to be noted in connection with timber:-

1) Converted timber :- This indicates timber which is sawn

and cut into suitable commercial sizes.

2) Rough timber:- This indicates timber which is obtained

after felling a tree.

3) Standing timber:- this indicates timber contained in a

living tree. (Timber has not been cut or sold)
Timber or wood as a building material possesses a number of valuable properties such as
low heat conductivity, amenability to mechanical working, small bulk density, relatively
high strength etc.

However it has its own drawbacks such as susceptibility to decay and inflammability,
fluctuations in properties due to change in moisture contents etc. These shortcomings of
timber can be reduced by application of modern wood processing techniques.

Every part of wood is very important including wood waste like saw dust etc.

Wood is the most unusual and valuable raw material of the building industry.
Classification of Trees
For the engineering purposes, the trees are classified according to their mode of
growth. The following is the classification :-

Trees

Exogenous Endogenous

Conifers Deciduous

Soft woods Hard woods

1. Exogenous trees:- These trees increase in bulk by growing outwards and distinct
consecutive rings are formed in the horizontal section of such a tree. The rings
are know as annual rings because one such ring is added every year and the rings
are useful in predicting the age of trees.

The timber which is mostly used for engineering purpose belongs to this
category.
The exogenous trees are further subdivided into two groups:-

a) The conifers:- are also know as ever-green trees and leaves of these trees do not
fall till new ones are grown. As these bear cone-shaped fruits , they are given the
name conifers. These trees yield soft woods which are generally light colored ,
resinous, light in weight and weak. They show distinct annual rings.
b) The deciduous:- are also know as broad-leaf trees and leaves of these trees fall in
autumn and new ones appear in spring season. The timber for engineering purposes
is mostly derived from deciduous trees. These trees yield hardwood which are usually
close-grained, strong, heavy, dark colored, durable and non-resinous. They do not
show distinct annual rings.
Soft woods and Hard woods:- The soft woods form a group of ever-green trees. The hard
woods form a group of broad-leaf trees. It is to be noted that the terms soft woods and hard
woods have commercial importance only. It is quite likely that some variety of soft woods
may prove to be stronger than some variety of hardwood

Comparison of Soft woods and Hard woods

S/N Item Soft woods Hard woods
1. Annual Rings Distinct Not distinct
2. Color Light dark
3. Fire resistance Poor More
4. Medullary Rays Indistinct Distinct
5. Strength Strong for direct pull and Equally strong for
weak for resisting thrust or resisting tension,
shear. compression and shear
6. Structure Resinous and split easily Non-resinous and close
-grained
7. Weight Light Heavy
2. Endogenous trees:- These trees grow inwards and fibrous mass is seen in their
longitudinal sections. The timber from these trees has very limited engineering
applications. The examples of endogenous trees are bamboo, cane, palm, etc.
Structure of a tree:-

A tree basically consists of three parts, namely Trunk, Crown and Roots. The function
of a
a) Trunk is to support the crown and to supply water and nutrients from the roots to
the leaves through branches and from the leaves back to the roots.
b) The roots are meant to implant the trees in the soil, to absorb moisture and the
mineral substances it contains and to supply them to the trunk.
From the visibility aspect, the structure of a tree can be divided into two categories:-
I. Macrostructure
II. Microstructure

I. Macrostructure:-
The structure of wood visible to the naked eye or at small magnification is called the
macrostructure. The image shows the transverse section of the trunk of an
exogenous tree.
 The following are its different components
1. Pith:- The inner most central portion or core of the tree is called the pith or medulla. It
varies in size and shape for different types of trees. It consists of cellular tissues and it
nourishes the plant in its young age. When the plant becomes old , the pith dies up and
decays and the sap is then transmitted by the woody fibers deposits round the pith.

2. Heart wood:- The inner annual rings surrounding the pith constitutes of the heart
wood. It is usually dark in color. As a matter of fact , it indicates dead portion of the tree
and as such it doesn’t take active part in growth of a tree. But it imparts rigidity to the
tree and hence it provides strong and durable timber for various engineering purposes.

3. Sap wood:- The outer annual rings between heart wood and cambium layer is know as
the sap wood. It is usually light in color and weight. It indicates recent growth and it
contains sap. It takes active part in the growth of a tree and the sap moves in an upward
direction through it. The sap wood is also know as the alburnum.
4. Cambium Layer:- The thin layer of sap between sap wood and inner bark is know as the
cambium layer. It indicates sap which has not yet been converted into sap wood. If the
bark is removed for any reason, the cambium layer gets exposed and the cells cease to
be active resulting in the death of tree.

5. Inner bark:- The inner skin or layer covering the cambium layer is know as the inner
bark. It gives protection to the cambium layer from any injury.

6. Outer bark:- The outer skin or cover of the tree is know as the outer bark, it is the
outermost protective layer and it sometimes contains cracks and fissures. It consists of
cells of wood fiber and is also know as the cortex .

7. Medullary rays:- The thin radial fibers extending from the pith to the cambium layer are
know as the medullary rays. The function of these rays if to hold together the annual
rings of the heart wood and the sap wood. The rays are sometimes broken and in some
variety of trees they are not very prominent.
II. Microstructure :-
The structure of wood apparent only at great magnifications is called the microstructure.
When studied under a microscope, it becomes evident that wood consists of living and
dead cells of various sizes and shapes.

The cells , according to the functions they perform , are classified into the following three
(3) categories:-

a) Conductive cells:- These cells serve mainly to transmit nutrients from the roots to the
branches and leaves .

b) Mechanical cells:- These cells are elongated , thick-walled and have tightly
interconnected narrow interiors cavities. The cells impart strength to the wood.

c) Storage cells:- These cells serve to store and transmit nutrients to the living cells in the
horizontal direction and they are usually located in the medullary rays.
 Felling of trees
To get timber , the trees are knocked down or cut down or caused to fall to the ground. This is
know as felling of trees

The important fact to be remembered in connection with felling of trees are as follows:-

1) Age of trees for felling:- The trees should be felled when they have just matured or when
they are very near to maturity. If they are felled before they attain maturity, the sap wood
would be in excess and the timber obtained from such trees would not be durable and it
will be in less quantity.

On the other hand it is not desirable to fell trees after they have fully matured as the heart
wood starts decaying after maturity. The age of good trees for felling varied from 50 to 100
years.
2) Method of felling:- The trees should be felled by experience person. The tree should be cut
from a place a little above its roots and very near to the ground level. Such a practice would
help in getting more timber from the trunk of trees

The process of felling of timber is as follows:-

i. A cut is made at the lowest possible point of the trunk and it is extended beyond the center
of gravity of cross-section of trees. This cut should be made on the side opposite to that on
which it is desired to fell the tree.
ii. Another parallel cut is made above the first cut in the opposite direction
iii. The top of the tree is then tied with ropes on all four diametrically opposite sides
iv. The rope on the side the tree is to be felled is pulled and at the same time, the rope on the
opposite side is slowly loosened.
v. By suitable swinging the tree, the trunk of tree will break at the level of the cuts and then it
is slowly allowed to fall gently on the ground. The workers should shift away when the tree
is falling to avoid any accidents.
vi. The branches are chopped off and the log is cut to the required sizes. Its bark is removed
and the log is sawn as early as possible.
3. Season of felling:- The trees should be felled when sap is at rest. The season for felling of
trees should be carefully determined by keeping in mind the climatic conditions of the
locality and types of trees.
In autumn and spring , the sap is in vigorous motion and hence the felling of the trees in
these seasons should be avoided. For hilly areas, the mid-summer would be the proper season
for felling trees as there is heavy rains in winter. For plain areas, the mid-winter would be the
proper season for felling as in summer, the water contained in sap would be easily evaporated
and it will lead to the formation of cracks.
Defects in timber:-

A defect is an irregularity or abnormality occurring in or on wood which is responsible for its

1. Strength reduction
2. Lowering of durability
3. Lowering of utility
4. Poor appearance
5. Decay

The defects occurring in the timber are grouped into the following five division:-

1) Defects due to conversion

2) Defects due to fungi
3) Defects due to insects
4) Defects due to natural forces
5) Defects due to seasoning
1. Defects due to conversion:- During the process of converting timber to the commercial
form, the following defects may occur:-

a) Chip mark:- This defect is indicated by the marks or signs placed by chips on the
finished timber surface. The may also be formed by part of the planning machine.

b) Diagonal grain :- This defect is formed due to improper sawing of timber. It is indicated by
diagonal marks on straight grained surface of timber
c) Torn grain:- This defect is caused when a small depression is formed on the finished
surface of timber by falling of a tool or so.

d) Wane:- This defect is denoted by the presence of original rounded surface on the
manufactured piece of timber
2. Defects due to fungi:- The fungi are minute microscopic plant organisms. They attack
timber only when the following two conditions are satisfied simultaneously :-
i. The moisture content of timber is above 20 percent
ii. There is presence of air and warmth for the growth of fungi

If any of the above condition is absent, the decay of wood due to fungi would not occur.
Following defects are caused in timber by fungi:-

a) Blue stain:- The sap of wood is stained to bluish color by

action of certain type of fungi
b) Brown rot:- The term rot is used to indicate decay or disease of timber. The fungi of
certain types remove cellulose compounds from wood and hence the wood assumes the
brown color. This is know as the brown rot.

c) Dry rot:- The fungi of certain types feed on wood and during feeding, they attack on
wood and convert it into dry powder form.
This is know as dry rot.
The following facts in connection with the dry rot are to be noted:-

i. The dry rot occurs at places where there is no free circulation of air such as improperly
ventilated basements, rooms etc. and in damp situations like kitchens and bathrooms.

ii. The unseasoned soft woods and sap wood are easily attacked by dry rot.
iii. If timber is not properly stored after being felled down, it is liable for the attack of dry
rot.
iv. The most favorable conditions for the rapid growth of fungus responsible for dry rot are
absence of sunlight, dampness, presence of sap, stagnant air and warmth.
v. The dry rot is also caused by charring, painting and tarring the unseasoned timber.
vi. The dry rot may be prevented by using well- seasoned timber free from sap.
vii. When part of timber is seriously affected by dry rot, the damaged portion may be
completely removed and the remaining unaffected portion should be painted with a
solution of copper sulphate.
d) Heart rot:- This is formed when a branch has come out of a tree . In such a case , the heart
wood is exposed to the attacks of the atmospheric agents. Ultimately the tree becomes
weak and it gives out hollow sound when struck a hammer.

e) Sap stain:- The fungi of certain types do not bring about the complete decay of timber, But
they feed on the cell contents of the sap wood. In doing so the sap wood looses its colors.
This is know as sap stain and it generally occurs when moisture contents goes beyond 25%
or so.
f) Wet rot:- Some varieties of fungi cause chemical decomposition of wood of the timber and
in doing so, they convert timber into a greyish brown powder. This is know as wet rot.

The important facts to be remembered in connection to wet rot are as follows:-

i. The alternate dry and wet conditions favor the development of wet rot
ii. If unseasoned or improperly seasoned timbers are exposed to rain and wind, they become
easily liable for attack of wet rot.
iii. To prevent wet rot, the well- seasoned timbers should be used for exterior work or for
underground works and it should be covered by tar or paint for protection against
moisture.
g) White rot:- This defect is just the opposite of brown rot. In this case, certain types of fungi
attack lignin of wood and the wood assumes the appearance of the white mass consisting
of cellulose compounds.
3. Defects due to insects:- The following are the insects which are usually responsible for
the decay of timber:-
i. 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
hardwoods. 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 also usually do not
disturb the outer shell or cover, hence the timber piece attacked by beetles may look
sound till it completely fails.
ii. Marine borers:- These are generally found in the salty waters. The most of the varieties
of marine borers do not feed on wood, But they make holes or bore tunnels on wood for
making shelter. The diameter and length of these holes may go has high as 25mm and
60mm respectively. The wood attacked by marine bores loses color and strength. It may
be noted that no timber is completely immune from attack of marine borers.

Piling attack from marine borers

ii. Termites:- These are popularly know as white ants and they are found in abundance in
tropical and sub-tropical countries. These inspects live in a colony and they are very fast
in eating away the wood from core of the cross-section. They make tunnels inside the
timber in different directions and usually do not disturb the outer shell or cover. Hence
the timber piece attacked by termites may look sound till it completely fails only few
very good timber can like teak wood resist the attack of white ant due to the chemicals
in their composition.
4. Defects due to natural forces:- The main natural forces responsible for causing defects
in timber are two, namely abnormal growth and rupture of tissues. Following defects
are caused by these forces:-

i. Burls:- These are also know as the excrescence and they

are particularly formed when a tree has received shock or
injury in its young age, due to such injury the tree is completely
upset and irregular projections appear on the body of timber.
ii. Callus:- It indicates soft tissue or skin which cover the wound of the tree.

iii. Chemical Stain:- The wood is sometimes discolored by the chemical

stain action caused with it by some external agency. This is know as the
chemical stain.

iv. Course grain:- If a tree grows rapidly, the annual rings are widened. It is know as the
coarse grained timber and such timber possesses less strength.
v. Dead wood:- The timber which is obtained from
dead standing trees contains dead wood. It is indicated
by light weight and reddish color.

vi. Druxiness:- This defect is indicated by white decay spots

which are Concealed by healthy wood. They are probably
formed by the access of fungi.

vii. Foxiness:- This defect is indicated by red or yellow tinge in wood

or reddish brown stains or spots round the pith of the tree discoloring the timber. It is caused
either due to poor ventilation during storage or by commencement of decay due to over-
maturity or due to growth of tree in a marshy soil.
viii. Knots:- These are the bases of branches or limbs which are broken or cut off from the tree.
The portion from which the branch is removed receives nourishment from the stem for a
pretty long time and it ultimately results in the formation of dark hard rings which are
know as knots. As continuity of wood fibers is broken by knots, they form a source of
weakness.
Classification of Knots on Size Basis
PIN KNOT ---------------------diameter up to 6.50mm
SMALL KNOT----------------- diameter up to 6.5 and 20mm
MEDIUM KNOT --------------diameter between 20 and 40mm
LARGE KNOT ------------------diameter greater than 40mm
Classification of Knots on Basis of form and quality

1. DEAD KNOT:-Knot which is separated from body of wood. It is not safe to use wood with
such a knot for engineering purposes.
2. DECAYED KNOT:-Popularly known as unsound knot and form by action of fungi on wood.
3. LIVE KNOT:-it is thoroughly fixed in wood and cannot separated out from body of Wood.
It is free from cracks and decay. Wood containing this knot can be used for engineering
purposes.
4. LOOSE KNOT:-It is preliminary stage of dead knot.
5. ROUND KNOT:-The cross-section of this type of knot is either round or oval
6. TIGHT KNOT:-It is preliminary stage of live knot. The fibers of knot are firmly held in
surrounding wood.
Types of knots
ix. Rind galls:- The rind means bark and gall indicates abnormal growth. Hence peculiar
curved swelling found on the body of the tress are know as the rind galls. They develop at
points from where branches are improperly cut off or removed. They are rarely found in a
tree and the timber in this part is very weak and not durable.

x. Shakes:- These are cracks which partly or completely separate the fibers of wood.
Following are the different variety of shakes:-
a) Cup shakes:- These are caused by rapture of tissue in a circular direction. It is a curved
crack and it separates partly one annual ring from the other. It develops due to non-
uniform growth or due to excessive bending of a growing tree during a cyclone weather. It
may not prove to be harmful if it covers only a portion of ring.

b) Heart shakes:- These cracks occur in the center of the cross-section of tress and they
extend from pith to sap wood in the direction of medullary rays. The cracks occur due to
shrinkage of interior part of tree which is approaching maturity. The heart shakes divide the
tree cross-section into two to four parts.

c) Ring shakes:- When cup shakes cover the entire ring, they are know as ring shakes .

d) Star shakes:- These are cracks which extend from bark towards the sap wood. They are
usually confined up to the plane of sap wood. They are wider on the outside ends and
narrower on the inside ends. They are usually formed due to extreme heat or severe frost
during the growth of the tree.
v. Radial shakes:- These are similar to star shakes , but they are fine, irregular and numerous.
They usually occur when tree is exposed to sun for seasoning after being felled down. They
run for a short distance from bark towards the center, then follow direction of annual ring
and ultimately run towards pith.
xi. Twisted fibers:- These are also know as wandering hearts and they are caused by twisting
of young trees by fast blowing wind. The fibers of wood are twisted in one direction. The
timber with twisted fibers is unsuitable for sawing, it can however be used for post and
poles in an unsawn conditions.

xi. Upsets:- These are also know as the raptures and they indicate the wood fibers which are
injured by crushing or compression. The upsets are mainly due to improper felling of the
tree and exposure of the tree in it young age to fast blowing winds.
xiii. Water stain:- The wood is sometimes discolored when it comes into contact with water.
This is know as the water stain and this defect is usually found in converted timber.

xiv. Wind cracks:- If wood is exposed to atmospheric agencies its exterior surface shrinks. Such
a shrinkage results into cracks.
5. Defects due to Seasoning:- The following defects occur in the seasoning process of
wood:-

i. Bow:- This defect is indicated by the curvature formed in the direction of the length of
timber.

ii. 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 usually occurs
in timber which are placed at the bottom during seasoning.
iii. Check:- A check is a crack which separates fibers of wood.
It does not extend from one end to the other.

iv. Collapse:- Due to uneven shrinkage, the wood sometimes

flattens during drying. This is know as collapse.

v. Cup:- This defect is indicated by the curvature formed

in the transverse direction of timber.
vi. 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 know as the
honey-combing.

vi. Radial Shakes:- These are radial crack as explained earlier.

vi. Split:- When a check extends from one end to the other it is
know as a split.
ix. Twist:- When a piece of timber has spirally distorted along its length, it is know as a twist

x. Warp:- When a piece of timber has twisted out of shape, it is said to have warped.
Qualities of Good Timber

In general the quality of good timber depends on the following factors

1) Environmental conditions locality

2) Maturity of the tree
3) Method of seasoning
4) Nature of the soil
5) Process of preservation and
6) Time of felling
Characteristics of qualities of Good Timber

1) Appearance:- A freshly cut surface of timber should exhibit hard and shining appearance.

2) Color:- The color of timber should preferably be dark. The light color usually indicates
timber with low strength.

3) Defects:- A good timber should be free from serious defects such as dead knots, flaws ,
shakes etc.

4) Durability:- A good timber should be durable. It should be capable of resisting the actions
of fungi insects, chemicals, physical agencies and mechanical agencies. If wood is exposed
to the actions of acids and alkalis for a prolonged period , it is seriously damaged.

5) Elasticity:- This is the property by which timber returns to its original shape when load
causing its deformation is removed. This property of timber would be essential when it is
to be used for bows, carriage shafts, sports goods, etc.
6) Fibers:- The timber should have straight fibers.

7) Fire resistance:- The timber is a bad conductor of heat. A dense wood offers good
resistance to fire and it requires sufficient heat to cause a flame. The heat conductivity of
wood is low and it depends on various factors such as porosity, moisture contents,
surrounding temperature, orientation of fibers, bulk density, etc.

8) Hardness:- A good timber should be hard i.e. it should offer resistance when its being
penetrated by another body. The chemicals present in heart wood and density of wood
impart hardness to timber. The mere resistance offered to chisel or saw does not usually
indicate hardness of timber.

9) Mechanical wear:- A good timber should not deteriorate easily due to the mechanical wear
or abrasion. This property of timber would be essential for places where timber would be
subject to traffic e.g. wooden floors, pavements, etc.
10) Shape:- A good timber should be capable of retaining its shape during conversion or
seasoning. It should not bow or wrap or split.

11) Smell:- A good timber should have sweet smell. An unpleasant smell indicates decayed
timber.

12) Sound:- A good timber should give out a clear ringing sound when struck. A dull heavy
sound when struck indicates decayed timber. The velocity of sound in timber is 2 to 17
times greater than that in air and hence wood may be considered high in sound
transmission. The sound conductivity is faster along the fibers, is lower in the radial
direction and is slowest along the cord of a cross-section.

13) Strength:- A good timber should be strong for working as structural members such as joist,
beam, rafter etc. It should be capable of taking loads slowly or suddenly. It should also
possess enough strength in direct and transverse directions.
14) Structure:- It should be uniform. The fibers should be firmly added. The medullary rays
should be hard and compact. The annual rings should be regular and they should be
closely located.

15) Toughness:- A good timber should be tough i.e. it should be capable of offering resistance
to the shocks due to vibrations. This property of timber would be essential when it is to be
used for tool handles, parts of motor cars and aero plans, etc.

16) Water permeability:- A good timber should have low water permeability which is
measured by the quantity of water filtered through a unit surface area of specimen of
wood. The water permeability is greater along the fibers than in other directions and it
depends on initial moisture contents, character of cut, types of wood, width of annual
rings, age of wood etc..

17) Weathering effects:- A good timber should be able to stand reasonably the weathering
effects. When timber is exposed to weather, its color normally fades and slowly turns grey.
A good timber should show least disintegration of the surface under adverse weather
conditions such as drying and wetting, extreme heat and cold , etc.
18) weight:- The timber with heavy weight is considered to be sound and strong.

19) Working conditions:- The timber should be easily workable. It should not clog the teeth of
saw and should be capable of being easily planed or made smooth,

The chief factors affecting the strength of timber are as follows:-

i. Abnormalities of growth
ii. Fault in seasoning
iii. Invasion of insects
iv. Irregularities of grain
v. Moisture contents
vi. Presence of knots, shakes etc.
vii. Way in which a timber piece is cut from the log, etc.
Decay of Timber

The timber is said to be decayed when it is so deteriorated that it loses its value as an
engineering material.

Following are the various causes or situations which favor the early decay of timber:-
a) Alternate dry and wet conditions..
b) Bad storage or stacking of timber.
c) Fungi which are responsible for developing diseases in timber such as blue stain, brown
rot, dry rot, heart rot, sap stain, wet rot and white rot.
d) Improper seasoning..
e) Insects such as beetles, marine borers, termites, etc.
f) Keeping timber in contact with damp wall, damp earth, etc.
g) Shocks or impacts received during young age from natural forces such as fast blowing
winds.
h) Use of timber without taking the sap wood from its structure.
i) Using seasoned timber without applying suitable preservative on its surface.
j) Using unseasoned wood with the application of protective coat of paint or tar.
Preservation of Timber
The preservation of timber is carried out to achieve the following three objects:-

a) To increase the life of timber structure

b) To make the timber structure durable and
c) To protect the timber structure from attacks of destroying agencies such as fungi, insects
etc.

Requirements of a good preservative:-

1. It should allow decorative treatment on timber after being applied on timber surface.
2. It should be capable of covering a large area with small quantity.
3. It should be cheap and easily available.
4. It should be durable and not affected by light heat etc.
5. It should be free from unpleasant smell
6. It should be non-inflammable
7. It should be quite efficient in killing fungi , insects , etc.
8. It should be safe and harmless for person or animals
9. It should give pleasant appearance to the timber after being applied over it.
10. It should not affect the strength characteristics of timber.
11. It should not be easily washed away by water
12. It should not corrode the metals with which it comes into contact
13. It should offer high resistance to the moisture and dampness.
14. Its penetrating power into wood fibers should be high. It is necessary for the preservative
to be effective to penetrate at least for a depth of 6mm to 25mm.

Types of Preservatives:-

a) Ascu treatment
b) Chemical salts
c) Coal tar
d) Creosote oil
e) Oil paints
f) So lignum paints
The Hazards Defined
The hazard to which wood material will be subjected has an enormous bearing on the extent
to which wood preservation will be effective. A piece of wood kept continually dry inside a
building is subject to a much lower hazard than a piece embedded in the ground.

Its broad categories, ranging from low to high hazard, are as follows:
(a) Interior timbers (i.e. indoors - framing, linings, joinery, etc.)

(b) Exterior timbers (i.e. outdoors above ground - cladding,

barge boards, window joinery, palings, rails, bridge decking, etc.).

TIMBER USED FOR LANDSCAPING IS USUALLY IN DIRECT GROUND

CONTACT AND IT IS RECOMMENDED THAT THEY ARE TREATED
WITH CCA OR CREOSOTE.
(c) Ground Contact (i.e. posts, foundation piles, poles, house stumps, crib walls, landscape
timbers, playground equipment, bridge and wharf timbers, etc.)

(d) Timber used in fresh water or heavy wet soil (i.e. poles for livestock pens, piling, jetties etc)

FOR MARIBE PILING, DOUBLE PRESSURE IMPREGNATION WITH CCA

FOLLOWED BY CREOSOTE IS REQUIRED.
1) Ascu Treatment:- This is aa special preservative which is developed at the research
Institute, Dehradun in India. Its compositions is as follows:-

1 part by weight of hydrated arsenic pentoxide, (𝐴𝑠2O5 , 2H2O)

3 parts by weight of blue vitriol or copper sulphate. (CuSO4 , 5H2O)
4 parts by weight of potassium dichromate, (K2Cr2O7) or sodium dichromate (Na2Cr2O7,
2H2O)

The material is available in powder form. To prepare a solution of this material , 6 parts by
weight of Ascu are mixed in 100 parts by water. The solution is then sprayed or applied on
timber surface. This preservative gives timber protection against attacks of white ants. The
surface treated with the preservative can be painted, polished , varnished or waxed. The
solution is odorless.
2) Chemical salts: These are water-borne preservatives and they are mostly salts dissolved in
water. The usual salts used are copper, sulphate, mercury chloride, sodium fluoride and
zinc chloride.
The solutions are prepared from these salts and then applied on timber surface, these
preservatives are odorless and non-inflammable . The treated surface can be painted or
varnished after drying. These preservatives have a good penetration and the treated timber
will show an immediate increase in weight

3) Coal Tar: The timber surface is coated with hot coal tar with the help of a brush. The coal
Tar becomes workable when heated. The process is know as the tarring. The coal tar has
unpleasant smell and appearance . It makes timber unsuitable for painting, Hence the
tarring is adopted for frames of doors and windows, rough timber work ,etc. and it is found
The creosote oil is one of the best antiseptic i.e. substance poisonous for wood attacking fungi.
It is highly toxic and gives out an unpleasant smell hence it should not be used for interior
surfaces of timber.
Creosote oil is flammable so, it is not used for timber works in fireplaces. It is generally used
for wood piles, poles, railway sleepers etc.

5) Oil Paints: The timber surfaces is coated with 2 or 3 coats of oil paint . The wood should be
seasoned. Otherwise sap will be confined and it will lead to decay
of timber. The oil paints preserve timber from moisture and
make it durable
6) So lignum paints: These paints preserve timber from white ants as they are highly toxic in
nature. They can be mixed with color pigments and applied in hot state with the help of a
brush. The timber surface may there be given the desired color or appearance.

Following are the six methods adopted for preservation of timber:

1. Brushing
2. Charring
3. Dipping and steeping
4. Hot and cold open tank treatment
5. Injecting under pressure
6. Spraying
1. Brushing: This is the simplest method of applying preservatives. For well-seasoned timber,
oil type preservatives are applied with good quality brushes. The cracks should be filled up
before the application of preservatives. For better penetration , the oil type preservatives
may be applied hot and the preservative should be liberally used on the surface . Several
coats of preservative may be applied , but interval should be given between the coats .

2. Charring: This method of charring is rather very old and as such, no preservative is used in
this method. The surface to be charred is kept wet for about half an hour and it is then
burnt up to a depth of about 15mm over a wood fire. The charred portion is then cooled
with water. Due to burning , a layer of coal is formed on the surface. This layer is not
affected by moisture and it is not attacked by white ants, fungi etc.
The disadvantages of this method are:-
i. The charred surface becomes black in appearance and hence it cannot be used for exterior
works
ii. There is some loss of strength of timber as the cross-section is reduced due to charring.

This process is generally adopted for lower ends of posts for fencing, telephone etc. which are
to be embedded on the ground or inserted in moist soil.

3. Dipping and steeping: In this method, the timber to be given preservative treatment is
dipped or soaked for s short period in the solution preservative. This method gives slightly
better penetration of preservative than in case of brushing and spraying. Instead of dipping
the steeping or wetting of timber with preservatives maybe carried out for periods varying
from a few hours to days or weeks. The depth of penetration of preservation depends on
the type of timber.
Dipping and steeping:

4. Hot and cold open tank treatment: In this method, the timber is submerged in a tank
containing solution of preservative which is heated for a
few hours at a temperature of 85°C to 95°C. The tank is then
Allowed to cool down gradually while the timber is still submerged
in the tank. This method is effective in giving protection to the
sap wood
5. Injecting under pressure: In this method, the preservative is injected under pressure into
the timber. This method is usually adopted in creosoting. This is the most effective method
of treating timber with the preservatives. But it requires special treatment plant. This
method proves to be essential for treating non-durable timbers which are to be used at
places where there is danger of attack by fungi and insects.

6. Spraying: In this method, the solution of preservative

is filled in a spraying pistol and it is then applied on timber
surface under pressure. The pressure works under compression air.
This method is also quite effective and it is superior
than brushing.
Fire-resistance of timber:
As a general rule, the structural elements made of timber ignite and get rapidly destroyed in
case of fire, they also add to intensity of fire. But the timber used in heavy sections may attain
high degree of fire resistance because the timber is a very bad conductor of heat.

With respect to fire –resistance , the timber is classified as refractory timber and
non- refractory timber. The refractory timber is non-resinous and it doesn't catch fire easily
e.g. teak wood etc. The non-refractory timber is resinous and it catches fire easily. The
examples of non-refractory timbers are fir etc.
To make timber more fire-resistant the following methods are adopted:-

1) Application of special chemicals: The timber surface is coated with solution of certain
chemicals. It is found that two coats of solution of borax or sodium arsenate with strength
of 2 per cent are quite effective in rendering the timber fire-resistant. These special
chemicals are know has the fire protection compounds or antipyrines and they are more
reliable.
When the temperature rises they either melt or give off gases which hinder or forbid
combustion
When the wood is treated with antipyrine, it doesn’t inflame even at high temperature, but it
merely smolders i.e. burn slowly without flame.

2) Sir Abel’s process: In this process, the timber surface is cleaned and it is coated with a
dilute solution of sodium silicate. A cream-like paste of slaked fat lime is finally applied on
the timber surface. This process is quite satisfactory in making the timber fire resistant.
Seasoning of Timber:
When a tree is newly felled, it contains about 50% or more of its own dry weight as water. This
water is in the form of sap and moisture. The water is to be removed before the timber can be
used for any engineering purposes.

• The process of drying of timber is known as the seasoning of timber and the moisture
should be extracted during seasoning under controlled conditions.

• It should also be seen during seasoning that the remaining moisture which cannot be
extracted, is uniformly distributed throughout the mass.

• If the drying is irregular, the shrinkage of timber will also be irregular and it will set up
internal stresses between the fibers

• When these stresses become excessive the timber warps and the shakes are formed.

• The wood is a hygroscopic material. The capacity of wood to absorb water vapors from air is
called hygroscopic of wood.
The dry wood absorbs the moisture from the surrounding air. The air humidity is not constant
and hence the wood moisture content also varies accordingly.

The fluctuation in moisture contents leads to cracking,, warping, swelling and shrinkage of
wood. Seasoned timber should be protected from exposure of the rain and excessively high
humidity.

Free moisture and bound moisture:

The moisture in timber can be present either in cell cavities or in cell walls. The former is know
as the free moisture or free water and major part of moisture in timber is present as free
water. The latter is know as the bound moisture and it is closely associated with the body of
timber.

When timber containing moisture is exposed to the atmospheric conditions, it starts losing its
moisture contents.

The free water is evaporated first and the point at which the cell cavity no longer contain free
Water is know as the fiber saturation point. After the fiber saturation point has been reached,
the tendency of timber to shrink appears and it is more or less proportional to the loss in
bound moisture.

Determination of moisture contents: The moisture content of timber is determined as

follows:-

𝑊1−𝑊2
p= x 100
𝑊2

Where P =percentage of moisture .

W1 = Original weight of timber.
W2 = Oven –dry weight of timber.

The samples of timber are taken in form of pieces having dimensions of 50mm x 50 mm x
25mm.
The seasoning of timber is carried out to achieve the following objects:

1) To allow timber to burn readily, if used as fuel.

2) To decrease the weight of timber and thereby to lower the cost of transport and handling.
3) To impart hardness, stiffness, strength and better electrical resistance of timber.
4) To increase the resisting power of timber, as most of the cause of decay of timer are more
or less related to moisture.
5) To maintain the shape and the size of the components of the timber articles which are
expected to remain unchanged in form.
6) To make timber easily workable and to facilitate operations during conversions.
7) To make timber fit for receiving treatment of paints, preservatives, varnishes , etc.
8) To make timber safe from the attack of fungi and insects.
9) To make timber suitable for gluing i.e. effectively joining two members of timber with aid
of glue.
10) To reduce the tendency of timber to crack, shrink and warp.
The method of seasoning can be broadly divided into two following categories:

1) Natural seasoning
2) Artificial seasoning

1. Natural seasoning: In this method, the seasoning of timber is carried out by natural air and
hence it is sometimes referred to as air seasoning.
The following procedures are adopted in air seasoning:

a. The timber in log form is not usually fit for the process of seasoning, hence it is cut and
sawn into suitable sections of planks or scantlings.
b. The timber piece can either be stacked horizontally or vertically the former arrangement
being very common
c. The ground, where stack is to be constructed , is cleared and it is leveled for good drainage.
d. The platform of stack is made slightly higher, about 300mm than the ground level, For this
purpose, the rows of bricks or concrete pillars are constructed. The pillars may also be
made of creosoted wood or coated wood with coal tar. The tops of pillars should be in the
same horizontal plane. The pillars should be durable.
e. The timber pieces are sorted out according to lengths and thickness. They are then
arranged in layer, one above the other. Care should be taken to see that all members in a
particular layer are of the same thickness. If precaution is not taken, there are chances the
timber to become warped or cracked.
f. Each layer is separated by spacers of sound dry wood. The usual dimension of spacer vary
from 35mm x 25mm to 50mm x 35mm. The larger dimensions being the width. The
spacers are to be placed in correct vertical alignment.
g. The distance between spacers depends on the sizes of timber members to be seasoned. It
is less for thin sections and more for thick sections. It usually varies from 450mm to
600mm
h. The length of stack is equal to length of timber piece. The width and height of stack are
restricted to 1.50m to 3 m respectively and a distance of 25mm is kept between adjacent
layers.
i. The stack is to be protected from fast blowing winds, rain and extreme heat of sun. Hence
Hence the stack should be preferably covered by roof of suitable material
j. Similar stacks may be constructed. The minimum distance between adjacent stacks should
be at least 600mm.

Advantages of Natural Seasoning:

i. Depending upon the climatic condition, the moisture content of wood can be brought
down to about 10 to 20 percent.
ii. It doesn’t require skilled supervision
iii. It is uneconomical to provide artificial seasoning to timber sections thicker than 100mm,
as such sections dry very slowly. Hence such thicker timber sections are usually seasoned
by the process of air seasoning.
iv. This method of seasoning timber is cheap and simple.
disadvantages of Natural Seasoning:

i. As the process depends on natural air, it sometimes become difficult to control it.
ii. The drying of different surfaces may not be even and uniform.
iii. If ends of thick sections of timber are not protected by suitable moisture –proof coating,
there are changes for ends splitting because the ends of such timber dry rapidly in
comparison to the central portions
iv. If not properly attended the fungi and insects may attack timber during the process of
seasoning and may thereby damage it.
v. The moisture content of wood may not be brought down to thee desired level
vi. The space required for this process will be more ,as timber will have to be stacked or
stored for a sufficiently long time.
vii. The process of seasoning is very slow and it usually takes about 2 to 4 years to make
timber fit for the work of carpentry .
2. Artificial seasoning: Following are the reasons for adopting the artificial seasoning to the
natural seasoning:

i. The defects such as shrinkage, cracking and warping are minimized.

ii. The drying is controlled and there are practically no chances for the attack of fungi and
insects.
iii. The drying of different surfaces is even and uniform.
iv. It considerably reduces the period of seasoning.
v. There is better control of circulation of air, humidity and temperature.
vi. The wood becomes more suitable for painting , gluing etc.
vii. The wood with desired moisture content may be obtained by artificial seasoning.
Various methods of artificial seasoning are as follows:

i. Boiling:- In this method the timber is immersed in water and water is then boiled. This is a
very quick method. The timber is thus boiled with water for about three to four hours. It is
then dried up slowly under a shed. The periods of seasoning and shrinkage are reduced by
this method, but it affects the elasticity and strength of wood.
ii. Chemical seasoning:- This is also know as the salt seasoning. In this method, the timber is
immersed in a solution of suitable salt. It is then taken out and seasoned in the ordinary
way. The interior surface of timber dries in advance of exterior one and chances of
formation of external cracks and reduced.
iii. Electrical seasoning:- In this method, the use is made of high frequency alternating
currents. The timber, when it is green, offers less resistance to flow of electric current. The
resistance increases as the wood dries internally which also results in the production of
heat. This is the most rapid method of seasoning. But initial and maintenance cost are
high.
iv. Kiln seasoning : In this method, the drying of timber is carried out inside an airtight
chamber or oven. The process of seasoning is as follows:-
1. The timber is arranged inside the chamber such that spaces are left for free circulation of
air.
2. The air which is fully saturated with moisture and which is heated to a temperature of
about 35°C to 38°C is then forced inside the chamber by suitable arrangement.
3. This forced air is allowed to circulate round the timber pieces. As air is fully saturated with
moisture , the evaporation from the surfaces of timber pieces is prevented. The heat
gradually reaches inside the timber pieces.
4. The relative humidity is now gradually reduced.
5. The temperature is then raised and maintained till the desired degree of moisture content
is attained.

Depending upon the mode of construction and operation, the kilns are two types, namely ,
stationary kilns and progressive kilns.

A. Stationary Kiln is also known as a compartment kiln and in this kiln, the process of
seasoning is carried out in a single compartment only. The drying operations are adjusted
as drying proceeds. This kiln is adopted for seasoning timber which requires a close control
of humidity and temperature. It gives a better results.
B. Progressive Kiln, the carriage with timber sections travels slowly from one end of the kiln
to the other and in doing so, it gets seasoned. The hot air is supplied from the discharging
end so that the temperature is less at the charging end and it increases towards the
discharging end. It is used for seasoning timber on a large scale.

The Kiln seasoning though costly gives well seasoned timber as it controls three important
conditions namely (Circulating air, relative humidity and temperature)

v. Water seasoning: In this method , the following procedure is adopted

a. The timber is cut into pieces of suitable sizes
b. These pieces are immersed wholly in water , preferably in running water of stream. The
care should be taken to see that the timber is not partly immersed.
c. The thicker or larger end of timber is kept pointing on the upstream side.
d. The timber is taken out after a period of about 2 to 4 weeks. During this period, the sap
contained in timber is washed away by water.
e. The timber is taken out of water and allowed to dry under a shed having free circulation of
air.
Different types of seasoning:

Chemical seasoning

Kiln seasoning

Water seasoning Boiling seasoning

Comparison between natural seasoning and kiln seasoning:
Conversion of timber:
The process by which timber is cut and sawn into suitable section is known as the conversion.
For this purpose , the power machines may be employed at different stages of process

Following are the important facts in connection with conversion of timber:-

1. The conversion is a skilled art and it should be carried in such a way that there is minimum
wastage of useful timber.
2. The allowance should be made for shrinkage, squaring and planning. It is about 3mm to
6mm.
3. The wooden beams should be sawn in such a way that they do not contain pith in their
cross-sections. To achieve this the timber is first sawn through pith into two halves.
4. To obtain strong timber pieces, the saw cuts should be made tangible to the annual rings
and practically parallel to the direction of the medullary rays.
5. The conversion may be achieved either by ordinary sawing, quarter sawing ,tangible
sawing or radial sawing
Fig. 9-4 shows ordinary sawing or bastard sawing or flat sawing or slab sawing. The saw cuts are tangential to the
annual rings and right through the cross-section of timber piece. The log is moved forward and backward on the
platform of a sawing mill. Thus the parallel cuts are made throughout the length of the log and parallel slices of
planks are obtained.

This is a very easy and quick method of sawing and it is widely adopted in our country. It is also most economical
method and wastage of useful timber is minimum. However the planks obtained by this method are liable to
warp and twist as a result of unequal shrinkage. The outer portion is of sap wood and it shrinks more.
 Fig. 9-6 shows tangential sawing or plain sawing or flat
The central portion is of heart wood and it
grained sawing. The saw cuts are tangential to the
shrinks less. Thus, the thickness at the center
annual rings and they meet each other at right angles.
remains almost unaltered while the
This method is adopted when the annual rings are
circumferential shrinkage causes warping and
very distinct and the medullary rays are not clearly
twisting of planks. Fig. 9-5 shows quarter sawing.
defined.

The saw cuts are at right angles to each other. It

The planks obtained by this sawing warp too much
may produce fine figure wood when adopted in
because the sections are weak as the medullary rays
case of timber having no distinct medullary rays.
which impart strength to the longitudinal fibers are
In this method, there is a tendency for the timber
cut. The timber obtained by this method is unsuitable
to bend in a transverse direction.
for flooring and it cannot be polished evenly.
Fig. 9-7 shows radial sawing or rift sawing. The saw cuts are made radially in a parallel
direction to the medullary rays. This method is used for conversion of hard timber. It
gives wood with decorative effect.

The timber obtained by this method shrinks and warps to a less degree and it is
distorted to the minimum. However the wastage is maximum and the cost of sawing
proves to be high as more time and labor are required in turning wood several times.

6. During conversion there will be loss of timber due to sawing it may extend up to 40% of reduction
of weight of log. The probable loss in conversion of timber from log to the required size of timber
may be taken as follows:
▪ Round log to planks………………………….40%
▪ Round log to scantlings …………………..50 %
▪ Square logs to planks……………………….30%
▪ square logs to scantlings………………….40%
Storage of Timber:
The structural timber should be properly stored so as to avoid any further development of
defects. For the purpose of storage, suitable stacks of timber pieces are formed. The stacks
are prepared on similar lines to the stacks for air seasoning as shown in fig. 9-16. The length of
stack depends on length of timber pieces. Its width and height are usually limited to about
1.50 m to 2 m respectively.

The material is arranged in layers and the layers are separated by wooden battens which are
known as the crossers or spacers. The stack should be protected from direct sun, dry wind
and rain. If necessary, a sloping roof of suitable material may be provided over the stack.

The important facts to be remembered for storage of timber are as follows:

(i) In each layer, an air space of about 25 mm should be maintained between adjacent
members.

(ii) The crossers or spacers should be of sound wood, straight and uniform in thickness.

(iii) The ends of all members should be coated with suitable material to prevent end-cracking.
(iv) The longer pieces should be placed in bottom layers and the shorter pieces should be
placed in top layers.

(v) The platform of stack should be made at least 150mm-300 mm higher than ground.

(vi) There should be a minimum distance of at least 300 mm-600mm between adjacent
stacks.
Market Forms of Timber:
The timber is converted into suitable commercial sizes.

Following are various forms in which the timber is available in the market:

(1) Batten: This is a timber piece whose breadth and thickness do not exceed 50 mm.

(2) Baulk: It is a roughly squared timber piece and it is obtained by removing bark and sap
wood. One of the cross-sectional dimension exceeds 50 mm, while the other exceeds 200 mm.

(3) Board: It is a plank i.e. a timber piece with parallel sides. Its thickness is less than 50 mm and
width exceeds 150 mm.

(4) Deal: It is a piece of soft wood with parallel sides. Its thickness varies from 50 mm to 100
mm and its width does not exceed 230 mm.
(5) End: This is a short piece of batten, deal, scantling, etc.

(6) Log: It is the trunk of tree obtained after removal of branches.

(7) Plank: It is a timber piece with parallel sides. Its thickness is less than 50 mm and its width
exceeds 50 mm.

(8) Pole: It is a sound long log of wood. Its diameter does not exceed 200 mm. It is also known
as a spar.

(9) Quartering: It is a square piece of timber, the length of side being 50 mm to 150 mm.

(10) Scantling: This is a timber piece whose breadth and thickness exceed 50 mm, but are less
than 200 mm in length. These are the pieces of miscellaneous sizes of timber sawn out of a log.
 Baulk

deal

Quartering Ends
Types of industrial Timber
The timber which is prepared scientifically in a factory is termed as the industrial timber and such timber
possesses desired shape, appearance, strength, etc.

Following are the varieties od types of industrial timber:-

(1) Veneers (2) Plywoods (3) Fiber Boards (4) Impreg Timbers(5) Compreg Timbers (6) Block Board and Lamin
Board (7) Glulam (8) Flushdoor Shutters (9) Particle Board or Chip Board (10) Hardboard.

(1) Veneers (IS- 303-1989):

These are thin sheets or slices of wood of superior quality. The thickness of veneers varies from 0.40 mm to 6
mm or more. They are obtained by rotating a log of wood against a sharp knife of rotary cutter or saw as shown
in fig. 9-21. The veneers after being removed are dried in kilns to remove moisture.
Following facts should be noted:

(i) The edges of veneers are joined and sheets of decorative designs are prepared.

(ii) The process of preparing a sheet of veneers is known as the veneering.

(iii) The veneers are used to produce plywoods, batten boards and lamin boards.

(iv) The veneers may be fixed on corners or bent portions. It creates an impression that the whole piece is made of
expensive timber.

(v) The veneers may be glued with suitable adhesives on the surface of inferior wood. The appearance of inferior
wood is then considerably improved.

(2) Plywoods:
The meaning of term ply is a thin layer. The plywoods are boards which are prepared from thin layers of wood or
veneers. The three or more veneers in odd numbers are placed one above the other with the direction of grains of
successive layers at right angles to each other. They are held in position by application of suitable adhesives. The
placing of veneers normal to each other increases the longitudinal and transverse strengths of plywoods.
While being glued, the pressure may be applied on veneers. The pressure may either be applied hot or cold.
For hot pressure, the hydraulic press is employed to press plywoods. The temperature varies from 150°C to
260°C. For cold pressure, the plywoods are pressed at room temperature only. The pressure applied on
plywoods varies from 0.70 to 1.40 N/mm2.

The plywoods are used for various purposes such as ceilings, doors, furniture, partitions, paneling walls,
packing cases, railway coaches, formwork for concrete, etc. The plywoods however are not suitable in
situations subjected to direct shocks or impacts. The use of plywood and its products has become so common
at present that it has totally changed the design and complex of various structures such as buildings, offices,
theatres, restaurants, churches, temples, hospitals, etc.

The plywoods are available in different commercial forms such as batten board, lamin board, metal faced
plywood, multiply, three-ply, veneered plywood, etc.

The batten board is a solid block with core of sawn thin wood as shown in fig. 9-22. The thickness of core is
about 20 mm to 25 mm and total thickness of board is about 50 mm. The direction of the grains of core
battens is at right angles to that of the adjacent outer ply sheets. These boards are light and strong. They do
not crack or split easily. They are widely used for making partition walls, packing cases, furniture pieces,
ceilings, shutters of doors and windows, etc.
 The lamin board is similar to the batten board except that the
core is made of multiply veneers as shown in fig. 9-23.

The thickness of each veneer does not exceed 6 mm and total

thickness of board is about 50 mm. The external plies are of thick
veneers and they are firmly glued with core to form a solid block.
The grains of core veneers are at right angles to those of outer
plies. These boards have the same uses as those of batten boards.

In metal faced plywood, the core is covered by a thin sheet of

aluminum, copper, bronze, steel, etc. This plywood is rigid and it
is cleaned.

The plywoods prepared from more than three-ply are designated

as the multiply. The number of veneers is odd. The thickness may
vary from 6 mm to 25 mm or more.
The plywoods prepared from three plies only are known as the three-ply. Its thickness is upto 5 mm.

The thickness of different plywood board in mm are as under:

3 ply – 4 mm
7 ply – 12 mm, 15 mm, 16 mm
9 ply – 12 mm, 15 mm, 19 mm
11 ply – 19 mm, 22 mm, 25 mm

Following are the rules regarding the thickness of plywood:

(i) For 3 ply boards, the combined thickness of face veneers should not exceed twice the thickness of the center ply.

(ii) In multiply boards, the thickness of veneer should not be more than thrice the thickness of any other ply.

(iii) The sum of thickness of wood with veneers in one direction shall approximately equal to the sum of thickness of
veneers at right angles to them and in any case, is should not be greater than 1.5 times this sum except for 3 ply given
above.

In veneered plywood, the facing veneer is of decorative appearance and it is used to develop an ornamental effect.
Advantages of Plywoods
(i) As plies are placed at right angles to each other, the expansion and shrinkage are comparatively very low.

(ii) They are available in a variety of decorative appearance.

(iii) They are available in large sizes. The commercial sizes have widths upto 1.50 m and lengths upto 3 m.

(iv) They are elastic and hence they are not liable to split or crack due to changes in atmosphere.

(v) They are light in weight.

(vi) They are not easily affected by moisture.

(vii) They are stronger than solid boards. For instance, a three-ply board is nearly three times stronger than the solid board of
the same thickness.

(viii) They are very easy to work and they can be made to suit any design.

(ix) They do not split in an axial direction.

(x) They do not split when nailed near edges because of their cross grained nature.

(xi) They make use of rare and valuable timbers in a quite economical way.
(xii) They possess uniform tensile strength in all directions.
(3) Fiber Boards:

These are rigid boards and they are also known as the pressed wood or reconstructed wood. The thickness varies from 3 mm to
12 mm. They are available in lengths varying from 3 m to 4.50 m and in widths varying from 1.20 m to 1.80 m. The weight of
Fiber boards depends on the pressure applied during manufacture. The maximum and minimum limits of weight are
respectively 9600 N/m3 and 500 to 600 N/m3.

Following is the procedure adopted in the manufacture of Fiber boards:

(i) The pieces of wood, cane or other vegetable fibers and chippings are collected and they are heated and boiled in a hot water
boiler.

(ii) The wood fibers separated by heat are put in a vessel.

(iii) The steam under pressure is admitted in the vessel.

(iv) The pressure of steam is then suddenly increased to 7 N/mm2. This increased pressure is maintained for few seconds only.

(v) The valve located at the bottom of vessel is opened and the steam is allowed to expand.

(vi) The sudden release of pressure makes the wood pieces to explode and in doing so, the natural adhesive contained in the
wood fibers is separated out.
(vii) The wood fibers are then allowed to flow out.

(viii) These fibers are cleaned of all superfluous or extra gums.

(ix) Such cleaned fibers are spread on wire screens in the form of loose sheets or blankets of required thickness.

(x) Such loose sheets of wood fibers are prepared between steel plates and ultimately, the Fiber boards are obtained.

Depending upon their form and composition, the Fiber boards are classified as insulating boards, medium hard boards, hard
boards, super hard boards and laminated boards. They are also available under various trade names such as Eureka, Indianite,
Insulate, Masonite, Nordex, Treetex, etc.

The Fiber boards form an ideal base for practically all types of decorative finishes such as distemper, oil paint, etc. The hard
boards are also suitable for polish and varnish. Several patterns of Fiber boards with pre-decorated surfaces are available in the
market and thus the necessity of treating them after fixing in position is eliminated.
Following are the uses of Fiber boards:

(i) For internal finish of rooms such as wall paneling, suspended ceilings, etc.

(ii) To construct formwork for cement concrete i.e. to retain cement concrete in position when it is wet.

(iii) To construct partitions.

(iv) To prepare flush doors, tops of tables, etc.

(v) To provide an insulating material of heat and sound.

(vi) To work as paving or flooring material

(4) Impreg Timbers:
The timber which is fully or partly covered with resin is known as the impreg timber. The usual resin employed
is phenol formaldehyde which is soluble in water. The veneers or thin strips of woods are taken and they are
immersed in resin. The resin fills the space between wood cells and by chemical reaction, a consolidated mass
develops.

It is then cured at a temperature of about 150°C to 160°C. The impreg timber is available under trade names
such as Formica, Sungloss, Sunmica, etc. and it is used for moulds, furniture, decorative articles, etc.

The advantages of impreg timbers are as follows:

(i) It is not affected by moisture and weather conditions.

(ii) It is strong and durable.

(iii) It possesses more electrical insulation.

(iv) It presents a decent appearance.

(v) It resists the acidic effects.

(vi) The contraction and expansion of impreg timbers are about 25 to 40 per cent less than ordinary timber.
(5) Compreg Timbers:

The process of preparing compreg timbers is same as that of impreg timbers except that curing is carried out
under pressure. The strength and durability of compreg timbers are more as compared to the impreg timbers. The
sp. gravity of compreg timbers is about 1.30 to 1.35.

(6) Block Boards and Lamin Boards:

Block boards are boards having a core made up of strips of wood, each not exceeding 25 mm in width. The edges
are glued together to form a solid sheet, which is then finished with one or two cross bonded veneers on each
face. The wooden strips may be obtained from small round wooden logs, leftovers from solid timber conversion or
peeler cores remaining from veneer production.

Grain direction of the core pieces is at right angles to that of the facing veneers. These boards are also known as
batten boards or solid core plywood, when the core strips consists of a core made up of large pieces of 80 mm
width.

These boards are extensively used for railway carriages, bus bodies, marine and river crafts, for furniture,
partitions, paneling, prefabricated houses, etc.

When the thickness of core strips does not exceed 7 mm, such boards are known as lamin boards.
(7) Glulam:

It means glued and laminated wood. It is not made of veneers but with solid wood. Solid wood is glued to large
sections. Glulam sheets are mainly used for supporting long span roofs in sports stadium, indoor swimming pools,
sheds for chemical factories, etc. where other materials like steel cannot last long. They can be used as beams of
many shapes including curved members. The timber sections are first dried in the kiln.

Then they are machined to form interlocking V-cuts across the width and the end sections of each piece. Suitable
glues are then applied and the pieces are forced together under longitudinal pressure, while the glue cures.
However for such type of fabrication, good shop facilities for woodworking and gluing are necessary and hence
they are not very popular in India.

(8) Flush Door Shutters:

In modern trends, factory-made flush door shutters have become more popular for interior work. They are
available in thickness of 25 mm, 30 mm or 35 mm.
Following different types of flush door shutters are available in the market:

(i) Cellular core type

(ii) Hollow core type
(iii) Block board core type; and
(iv) Particle or MDF board core type.
(9) Particle Boards or Chip Boards:
These boards are made of wood particles or rise husk or bagasse (remains of sugarcane after crushing), embedded
in resins and subjected to heat with pressure. These boards are manufactured by extrusion pressing or by pressing
in parallel plates.

The extrusion pressing process orientates the wood particles in the direction at right angle to the plane of the
board, while pressing in parallel plates orientates the particles parallel to the plane of the board.

Following are the four types of particle boards:

(i) Flat pressed single layer board – FP SL

(ii) Flat pressed three layer board – FP TH

(iii) Extrusion pressed solid board – XP SO

(iv) Extrusion pressed tubular core – XP TU

Particle boards are heavier than solid wood plywood. As they provide broad and stable panels of reasonable
strength, they can be sawn like wood and are mainly used for furniture making.
(10) Hard Boards:
Hardboard is made from wood pulp which is compressed to make sheet usually of 3 mm thick. Its face surface
is made smooth and hard while back surface is made rough with pattern or cross lines. Its width is usually 1.2
m and length varies from 1.2 m to 5.5 m.

Table 9-7 shows classification and thickness of hardboard as per CPWD specifications.
Advantages of Timber Construction:
The timber has been probably the first material to be adopted in the construction of engineering structures.

It possesses the following distinct advantages in preference to other engineering materials:

(i) It can be easily handled and can be planed, sawn and joined with ordinary tools of the carpenter.

(ii) It can be used either for load bearing members or for non-load bearing members.

(iii) It combines light weight with strength and hence it is generally preferred for the buildings in the earthquake-
prone regions.

(iv) It is easy to provide connections in the timber construction.

(v) It is economical and cheap. This is due to the fact that the smallest piece of wood can be put to one or other
use and the wastage of material is thereby considerably minimized.

(vi) It is possible to realize some value even after timber construction has completed its useful life.

(vii) It is used to prepare furniture of decent appearance and comfortable design.

(viii) The heavy timber construction presents a massive appearance.

(ix) The houses with timber construction are found to be cool in summer and warm in winter. This is due to the
fact that the wood is a non-conductor of heat.

(x) The other forms of present-day such as plywoods, Fiber boards, etc. have made timber construction to match
with the present-day requirements.

(xi) The timber construction is quite durable, if properly protected against moisture, rain, wind, etc.

(xii) The additions, alterations and repairs to the timber constructions can be carried out easily.

(xiii) It is found to be superior to the cement concrete and steel in respect of thermal insulation, sound
absorption and electrical resistance. For instance, the thermal insulation of wood is 15 times better than
concrete, 6 times better than bricks and 1770 times better than aluminum.

(xiv) It is also highly energy efficient. The amount of electricity or its equivalent required for the production of
one unit of timber is nearly 6.25 times less than that required for steel and about 40 times less than that
required for aluminum.

(xv) It is easily available and can be speedily transported by simple means of communication.
It should however be remembered that every effort should be made to use timber as economically as possible and
thus to minimize its wastage. The production processes and working conditions should be judiciously decided and
scientifically designed.

The important steps to be taken to increase the durability of wood and its structures are adequate temperature and
moisture, proper inspection and maintenance, treatment of exposed surfaces, provision of favorable working
conditions, etc.

The disadvantages of timber construction are as follows:

(i) It is likely to crack, warp and decay, if not properly seasoned and not treated with the preservatives.

(ii) It is not suitable for cyclonic weather and for places subjected to the natural calamities.

(iii) It requires careful regular maintenance.

(iv) It is subjected to the risk of fire.

(v) If not locally available, it proves to be costly.

Uses of Timber:
There is hardly any material other than timber which can be used as an all-round substitute in
construction work and its various uses can be summarized as follows:

(i) It is used for door and window frames, shutters of doors and windows, roofing materials, etc.

(ii) It is used for formwork of cement concrete, centering of an arch, scaffolding, etc.

(iii) It is used for making furniture, agricultural instruments, sport goods, musical instruments,
etc.

(iv) It is used for making railway coach wagons.

(v) It is used for making toys, engraving work, matches, etc.

(vi) It is used for railway sleepers, packing cases, etc.

(vii) It is used for temporary bridges and boat construction.

Door & window frames For musical instruments
Roof framing

For toys

Timber framing For boats