2. Woodis probably the first material and one of the most used materials to be employed in the
construction field. In the building up of structures, the use of wood is almost indispensable.
(a) Temporarily to facilitate the construction and
(b) As a permanent component part of completed ones. It is necessary to study the wood material and its
structure, to understand the durability and methods of preservation, strength and uses to which each
variety of wood could be put to advantage, and also the various manufacturing processes of modern
materials like reconstructed wood, etc.Trees yield wood, which is an extremely adaptable material as it
provides fuel, fibre, and chemical derivatives and serves as a unique structural material.
Wood suitable for use as structural material is called timber.Timber is obtained from trees.
4. A standing living tree is known as standing timber and when the tree has been cut and its stem in branches are
roughly converted into pieces of suitable length, it is known as rough timber.When the rough timber is further
sawn and converted into various forms and sizes viz. plank, logs, battens, beams, etc. it is known as converted
There is a difference between the two terms - timber and wood.
Wood includes all types of wood that may be burning wood, structural wood, furniture wood, etc.The wood that
is suitable for use as a structural material is called timber.
Exogenous tree Trees falling in this category yield timber for structural purpose.The growth of these trees is
i.e. they increase in bulk by the formation of successive annual rings on the outside under the bark.The section of
such trees shows distinct consecutive rings which are known as annual rings. Every year, a new ring is added to the
section of the tree.The number of annual rings shows the age of the tree at the time of its felling.These trees are
further sub divided into two:
5. - Conifers treesThe conifers trees are also known as evergreen trees as the leaves of these trees do not fall till
the new ones are grown.These trees have pointed, needle like leaves and bear cone shaped fruits.
- These trees yield softwood.
- Deodar, fir, pin, cedar, etc. are some of the typical examples of trees in this group.
Endogenous treesThese trees grow inwards by depositing each fresh layer internally.
Thus the older formation of wood material is on the outside.
The timber obtained from these trees has very limited engineering applications and is generally used for
temporary construction.The most common variety of these trees is coconut, bamboo, cane, palm, etc.
Structure of tree A tree basically consists of three parts namely the trunk, the crown, and the roots.
The function of the trunk is to support the crown and to supply water and nutrients from the roots
to the leaves through the branches and from the leaves back to the roots.The function of the root is
to implant the tree in the soil and to absorb the moisture and mineral substances from the soil and
then supply them to the trunk.The structure of the tree can be divided into two categories:
Macrostructure is the structure of wood that is visible to the naked eye.A timber tree consists of a
bundle of fibres, which run parallel to the length of its stem and branches.The fibres, which are also known
as cells, are in the form of hollow tubes that are arranged in an irregular manner round the center of the
tree.The function of these cells is to lend strength to the stem and conduct sap from the roots to the
leaves and branches.The central part of the tree is very soft and is known as pith or heart. Surrounding
the pith is the heartwood. Heartwood consists of innermost annual rings and is the most strong, durable
and compact portion of the tree.The portion of timber that is enclosed between the heartwood and the
cambium layer is known as sapwood. Sapwood is lighter in colour and is comparatively lighter in weight.
This wood is of recent growth and contains a lot of sap.The annual rings in this wood are less sharply
defined than those of heartwood.A thin layer of sap between the sapwood and the inner bark is known as
the cambium layer.This layer is a sap, which has yet not been converted into sapwood. 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 the tree.The thin layer covering the cambium layer is known as the inner bark.This protects the
cambium layer from any injury.The outermost layer of the wood round the tree is known as bark. Bark is
layer of corky tissue of timber and provides protection to the stem from abrasion and temperature
changes.The fibers which radiate from the bark towards the centre of the tree are known as medullar rays.
These rays help to hold the annual rings together.
The microstructure of wood is the structure studied under a microscope which reveals that wood
consists of living and dead cells of various shapes and sizes.The cells are of three types:
1. Conductive cells,
2. Mechanical cells &
3. Storage cells.
1. Conductive cells:These cells transmit the nutrients from the roots to the branches and the leaves of the tree.
2. Mechanical cells:These cells are elongated and thick walled and impart strength to the wood.
3. Storage cells:These cells serve to store and transmit nutrients to the living cells in the horizontal direction.
They are usually located in the medullar rays.
9. Felling of trees
The systematic and careful cutting of trees is called as felling of trees.The best time of felling tree is after they have
reached full age. If cut too young the trees yield soft wood, which is liable to decay due to the presence of sap in it.
On the other hand, if the tree is not cut when fully matured, and is allowed to grow older, the hardwood starts
decaying and the quality Felling of tree of timber yielded is weak, crisp & brittle.The best time for cutting is when the
sap has ceased to circulate or when the sap is at rest that is in midsummer or
10. Advantages of Timber
Timber has the following advantages: -
It is easily available and can be quickly transported by simple means.
- It can be easily worked with tools to any size.
- Addition, alteration and repairs to timber construction can be easily done.
- It is used for repairing furniture and is an excellent material for decorative and artistic interior fitting
- It is a good sound absorbing material.
- It is economical as even the smallest piece of wood can be utilized thereby minimizing the wastage
- It is quite durable if protected from direct exposure to sun and rain and to alternate wet and dry
- It has a combination of lightness, strength and durability. It has a good resale value.
- Houses built of timber are warm in winter and cool in summer due to the nonconductive
property of wood.
- It can be universally employed for both load bearing and non load bearing members with equal
11. Disadvantagesof Timber
It requires regular, careful maintenance.
If not properly seasoned or not treated with preservatives, it is likely to crack, warp, and decay.
It is subjected to risk of fire.
12. Conversion ofTimber
The process by which the timber is cut and sawn into suitable sizes is known as conversion of timber.After felling,
the stem and major branches are cut into logs of suitable lengths.These logs are then transported to a saw
machine and converted into marketable sections.The conversion of timber is done at sawmills.The conversion is a
skilled art and should be done in such a way that the wastage of timber during sawing is the minimum. Conversion
of timber is done by sawing in the following
13. a. Ordinary sawingThis is also known as flat, slab, or bastered sawing.This method is very easy, quick and
economical method of sawing and is widely adopted in our country.The log is moved forward and backward in
the same position on the sawing platform resulting in number of parallel slices of planks.The wastage of timber in
this method is minimum. However, the planks obtained by this method are liable to warp and twist on drying.The
outer portion of sapwood shrinks more while the central portion of heart wood shrinks less.This makes the
wooden planks thin at the edges and thick in the middle.This uneven shrinkage causes warping and twisting of
14. b. Quarter SawingThis type of sawing involves sawing of timber by first cutting the log in quadrants of circles. Saw cuts
are given at right angles to each other.This method involves least wastage of useful timber
This type of sawing is also termed as plain sawing.The saw cuts
are given tangential to the annual rings and right angles to the
medullary rays.This method is adopted when the annual rings
are very distinct and medullary rays are not clearly defined.The
planks obtained by this method of sawing are weak and warp
too much as radial or the medullary rays, which impart binding
and unity to the longitudinal fibers are cut.The timber obtained
by this method does not take even polish and is easily
15. Radial sawing
The strongest and the most durable timber are obtained by the radial sawing method.The saw cuts are made
radically in a parallel direction to the medullary rays and perpendicular to the annual rings.Timber obtained by this
method of sawing, shrinks and warps less. But the cost of manufacture increases due to more wastage and more
time and labor to turn the logs several times during sawing.This method of sawing is used for conversion of hard
timber.The wood obtained by this method is suited for high-class work.
16. Defects in Timber
Defect in timber has a general effect in decreasing the strength and durability. Such timber fetches a very low price
and is unsightly in appearance.The common defects are: • Natural defects • Defects arising during conversion and
careless storage • Defects due to fungal action and insects • Defects due to improper and careless use.
Natural defectsThese are due to imperfection in growth, abnormal growth, rupture of tissues, injuries, etc.These
defects develop during the growth of the tree and they affect the strength of the timber.Various defects are given
→ ShakesThese are cracks that partly or completely separate the fibre of wood. Following are the different
varieties of shakes:
(a) Star Shake:These are cracks that extend from the bark towards the sapwood.These splits or cracks are
usually confined up to the plane of sapwood only - the cracks are widest at the circumference and then go on
narrowing as they proceed towards the center of the tree. Star shakes are usually formed due to extreme heat
or severe frost during the growth of the tree.The logs having this defect when sawn usually separate out into a
number of pieces and hence become useless.
17. b) Cup Shake:
This defect is probably caused by the sudden contraction of timber under atmospheric changes, due to the swinging of
the tree against strong winds. Cup shakes usually appear in the form of curved cracks or splits that partly separate one
annual ring from the other.The crack or split does not run for the full circumference of the annual ring.
(c) Ring Shake:When the cup shake defect runs for the full circumference of the annual ring, it is called as ring shake.The
adhesion between two annular rings is thus lost.
18. (d) Heart Shake:
These defects are termed as heart shake as they occur in heartwood.The heart shake is the most common defect and
it is liable to exist in almost every type of tree.These splits or cracks occur in the central part of the tree.These splits
or cracks are widest at the centre and go on narrowing as they proceed towards the outer circumference.This defect
usually occurs in over matured trees.
(e) Radial Shake:
The heartwood is lost by evaporation and the wood starts drying from the pith
outwards.The heart shake divides the tree in cross section into several parts.
(f) Radial Shake:These defects are similar to star shake. If the outside of the wood dries
quickly, the radial cracks occur extending from the sapwood toward the heartwood.
These cracks generally appear when the felted tree is exposed to the sun for seasoning.
19. (g) Twisted Fibre:
These defects are caused by the strong winds, constantly turning the trunk of the tree in one direction as shown in
the figure.The fibres of the wood are twisted in one direction.Timber having these defects is unsuitable for sawing.
However, it can be used for posts and poles in an un-sawed condition.
(h) Upsets:These are also known as ruptures.The upsets are mainly due to improper felling of tree and exposure of
the tree in its young age to the fast blowing wind.This defect is caused due to injury to the wood fibres by crushing or
compression.This defect indicates change in the direction of wooden fibres.
20. (i) Wind Cracks: Due to the atmospheric changes, the exterior surface of the standing trees shrinks.This causes
cracks on the outer surface only.These cracks are known as wind cracks.
(ii) (j) Ring Gall: Rind means bark and gall indicates abnormal growth. Hence, curved swellings found on the body of the
tree are known as ring gall.They are usually caused by the irregular growth of layers over the wounds left after the
branches have been cut off or removed in an irregular or improper manner.This defect is rarely found in a tree and
the timber in this part is very weak and not durable.
21. (k) Knots:
Knots are generally developed at the basis of branches, which are broken or cut off from the tree.The wood fibre
from where the branch has been removed receives nourishment from the stem for a pretty long lime.This results in
the formation of dark, hard rings, which are known as knots. Knots are the most common defects of wood.As knots
break the continuity of the wooden fibres, they disturb the homogeneity of wood texture and thus form a source of
weakness.The fibres of wood get twisted in the region of knots and this affects the strength of the wood.The
magnitude of the reduction in strength that the knots can cause depends upon the position, the size of the knot and the
degree of grain distortion around it. It is rather impossible to
procure converted timber without knots.
22. • Defects Arising During Conversion and Careless StorageThe conversion of timber is done almost
immediately after felling the tree.The defects that may develop after felling the tree and also during conversion
are as follows:
(a) Bow:When the planks of converted timber shrink and bend in converted form, in the direction of length,
the defect is called bow.
b) Cup:When the wooden planks bend in converted, in
transverse direction the defect is called cup.
23. (c) Twist:When the wooden planks distort spirally along the length, the defect is known as a twist.
When a plank of timber has twisted out of shape, it is said to have
warped. (e) Case Hardening:The upper surface of the timber that is
exposed to the atmosphere dries very quickly.Therefore it shrinks
and is subjected to compressive stresses, the interior surface of
timber dries very slowly as it is not exposed and is thus under
tension. Due to the unequal shrinkage of internal and external
surfaces, the timber is subjected to stresses and strains.This defect is
known as Case Hardening, it usually occurs in the bottom sections of
the heavily loaded stacks that are kept for seasoning. (f) Honey
combing defects:When the radial and circular splits or cracks that
have developed in the internal portion of the timber intersect each
other, a honey comb texture is imparted to the wood.The defect so
developed is known as honey combing defect.
24. • Defects
Due to Fungal Action and Insects Fungi are minute microscopic plant life or plant organisms that attack and
live on wood tissues and their cell contents. Rotting is the disintegration and destruction of wood material
by fungal action.Air, warmth, moisture and food (organic components of wood) are the main factor’s that
promote the attack by fungi or micro-organisms. Decomposition of timber may be caused by certain insects
also. Such insects are beetles, marine borers and termites or white ants. Beetles and termites live on wood
materials, whereas the Marine borers bore holes in the wood for them to live in without eating it. Poor
ventilation, dampness and warmth encourage the insect attack.
• Defects Due to Improper and Careless Use The decay of
timber may be due to the following:
(1) Careless handling of unseasoned timber after felling.
(2) Improper seasoning.
(3) Alternate dry and wet conditions.
(4) Bad storage or stacking
(5) Using timber in structure without painting or protective
covering. of timber.
25. (k) Knots:
Knots are generally developed at the basis of branches, which are broken or cut off from the tree.The wood fibre
from where the branch has been removed receives nourishment from the stem for a pretty long lime.This results
in the formation of dark, hard rings, which are known as knots. Knots are the most common defects of wood.As
knots break the continuity of the wooden fibres, they disturb the homogeneity of wood texture and thus form a
source of weakness.The fibres of wood get twisted in the region of knots and this affects the strength of the wood.
The magnitude of the reduction in strength that the knots can
26. Preservation ofWood
The preservation of timber is carried out to increase the life of timber structures and to make them durable
by protecting them from insect attack, fungal infection and diseases of timber. Preservative acts like as a
disinfectant.The following are the two main classes of wood preservatives. Water soluble preservatives
containing organic or inorganic salt. Oil preservatives - The efficiency of the preservative treatment depends
upon the proper choice of the preservatives and the method of its application.Timber for preservative
treatment should be seasoned to the desired moisture content and fabricated to the required sizes.
27. Seasoning of Timber
A freshly felled tree contains a lot of moisture in the form of sap.This excess moisture has to be removed for
better use of timber.The process of reducing the moisture content from the timber to prevent it from the
possible decay is known as ‘Seasoning’.The moisture content of the timber is reduced to such an extent that
moisture contained in seasoned timber corresponds to the moisture content in the atmosphere, where the
timber is to be used. Following are the advantages of seasoning
- 1. It makes the timber light in weight.
- 2. It is easy to handle and transport.
- 3. It improves the properties of timber by giving strength and the timber becomes more stable.
- 4. It improves the resistance to fungi, insect attack.
- 5. It improves the workability of timber.
- 6. It reduces the tendency of timber to stack.
- 7. It reduces the tendency of timber to shrink.
- 8. It reduces the tendency of timber to warp.
- 9. It takes good finish of paints, varnishes.
- 10. It is ready for the engineering work.
- Seasoning can be done by various methods.The methods of seasoning are mainly classified into two
categories. (a) Natural seasoning and (b) Artificial seasoning
28. (a) Natural seasoning
In this method of seasoning the big logs of tree are converted into small planks.These planks are stacked
under a covered shed (preferably with open sides, about one foot above the floor).The planks are stacked in
such a manner that it allows the free circulation of air through them.The planks are placed in layers across
each other as shown in the figure. Generally, the wood takes about two to three months.The hard wood
takes about one year for every 25cm.The time required for this type of seasoning varies as per the climatic
condition, the size of timber to be seasoned, type of wood, etc. Natural method of seasoning is very
economical than the other methods of the seasoning.This method of seasoning has advantages as well as
29. Advantages of natural seasoning
(a) No factory setup is required.
(b) No skilled supervision is required.
(c) It is very economical.
(d) The thick tags can be seasoned by this method.
(e) No machinery is required.
(f) It is pollution free.
(g) Electricity is not required.
Disadvantages of natural seasoning (a) The seasoning process depends upon the natural air circulation and
therefore it cannot be controlled. (b) Seasoning by this method may not be uniform and even. (c) It requires
very large space for stacking the logs for seasoning
30. (b) Artificial seasoning
To overcome the time factor required in natural seasoning, the artificial seasoning was developed.This
method is opted for rapid seasoning. In this method, kilns are used. First of all, the planks to be seasoned are
stacked in the kiln in such a way that there is free space for air accusation around the stacked timber planks.
After this, hot air containing a certain amount of moisture is circulated through the stacked timber planks in
the kiln.The circulated air of controlled humidity takes up the moisture from the plank of timber and
seasons them.Advantages of artificial seasoning
(a) Drying process of the seasoning can be controlled.
(b) Timber becomes resistance to fungi and insect attack.
(c) This method is very fast as compared to natural seasoning
(d) The surface of the seasoned timber is more uniform.
(e) It takes better finish of paint and varnish
31. Characteristics of good timber
Following are the characteristics of good timber:
1. It should be hard and durable.
2. It should be from the heart of a well-matured tree.
3. Its colours should be uniform.
4. It should be capable of resisting the action of fungi, chemicals and physical agencies.
5. It should be free from large knots, dead knots, shakes, tows or blemishes of any kind.
6. Its weight should be heavy.
7. It should be elastic
8. It should be property seasoned.
9.A fresh cut should smell sweet.
10. It should be capable of resisting weathering affect
32. Wood Products
The timber is converted into commercial sizes for use other than the logs and the planks. Other commercial products
made from timber are known as wood products. Following are the forms of wood products:
(a)Veneers:Veneers are thin layers of timber cut from a very good quality of timber.Thickness of the veneer may vary
from 0.4 mm to 6mm. Generally the veneer is sliced off from the tree like teak, rosewood, oak, mahogany, etc.The
veneers are used for covering the furniture of inferior quality
timber for better look.
(b) Plywood: Ply is a thin layer of timber. Ply is made up of gluing odd number of sheets together in such a way that
the directions of the grains cross each other.
The glue used for binding the ply determines the quality of the ply.Thus we have commercial ply, waterproof
ply, anti-termite ply, etc.The ply is generally manufactured in 3,5,7… and so on.The commercial thickness of ply
is 6 mm to 18 mm and can be more if required.The size of the ply varies from 90cm X 90cm to 240 cm X 240
33. (c) Fibre board:These boards are made up of wood and other vegetable fibres.The pulp of the fibres is boiled and
then pressed together in various thicknesses.The various types of fibre board include hard board; insulating board,
plaster boards, etc.
34. (d) Block board:They consist of core made of small timber blocks up to 25 mm thickness.The edges of it are glued
and both the sides are covered with thin plywood of 3mm thickness.The direction of the ply on the sides is at
right angles to the inner core.
(e) Batten board:These boards have similar construction as that of the block board; the inner core is made up of
2 and 3cm thick and the sides are covered with the ply.These boards are used as door panels, for shelf etc.They
are light in weight and strong.
35. (f) Hard board:These boards are manufactured by using the waste from the sawmill.The waste of the saw mill is boiled
and converted into small fibres and the proceeds fibres are converted into boards by using hydraulic pressure.Width of
the sheet is usually 1.25m and 1.75m, maximum length available is 4.75m and thickness varies from 2mm to 20mm. Hard
boards are used for suspended ceilings, table tops, counter tops, interior and exterior wall panels, etc.
(g) Medium-density fibreboard (MDF):These boards are made up of hardwood or softwood and other vegetable fibres.
Pieces of wood and other vegetable fibres are boiled and then pressed together in various thicknesses with wax and a
resin binder. Panels are formed by applying high temperature and pressure.These boards are generally stronger and much
denser than particle board or plywood.The various types of fibre board include hard boards, insulating boards, plaster
• Advantages of MDF - It is a superb alternate for veneers. It has stable dimensions i.e. no expansion or contraction
like wood as also regular in strength and size. It shapes well and is flexible i.e. it can be used for curved walls or
surfaces. It is easy to finish with paint. Some of the varieties are less expensive than many natural woods. • Uses of
MDF – to construct partitions, wall panels and suspended ceilings, as table tops, as an insulating material against
heat & sound, for flush doors, etc.
36. Laminates are thermo-set composite sheets generally called High Pressure Decorative Laminates (HPL).These sheets are
made of numerous layers of paper saturated with thermosetting resins and bound by the combined action of heat and high
pressure.These sheets are homogeneous, non-reactive, non-porous, high density, rigid sheets with high resistant to
abrasions, scratches, impact and ageing due to light.The melamine impregnated decorative paper used as the surface gives it
an attractive look. Laminates applications Associate High Pressure Laminates are used in all types of interior décor
applications like furniture, tabletops, counter-tops, study tables, office furniture, kitchen cabinets, partitions, wardrobes,
doors, industrial products and more.They can be used to laminate or cover the surface of any appropriate substrate
material like chipboards, plywood, MDF boards, OSB,WPC boards, walls, etc.
Size in MFC 8′x4′
SurfaceTextures ST Matt, Silk, Suede, etc
37. Defects in Timber Defect in timber has a general effect in decreasing the strength and durability. Such timber fetches
a very low price and is unsightly in appearance.The common defects are:
• Natural defects
• Defects arising during conversion and careless storage
• Defects due to fungal action and insects
• Defects due to improper and careless use
• Natural defectsThese are due to imperfection in growth, abnormal growth, rupture of tissues, injuries, etc.These
defects develop during the growth of the tree and they affect the strength of the timber.Various defects are given
38. Types of veneersThere are a few types of veneers available, each serving a particular purpose.
• Raw veneer has no backing on it and can be used with either side facing up. It is important to note that the two
sides will appear different when a finish has been applied, due to the cell structure of the wood.
• Paper backed veneer is as the name suggests; veneers that are backed with paper.The advantage to this is that it is
available in large sizes or sheets, as smaller pieces are joined together prior to adding the backing.This is helpful for
users that do not wish to join smaller pieces of raw veneers together.This is also helpful when veneering curves and
columns as the veneer is less likely to crack.
• Phenolic backed veneer is less common and is used for composite or manmade wood veneers. Due to concern for
the natural resource, this is becoming more popular. It too has the advantage of being available in sheets, and is also
less likely to crack when being used on curves
. • Laid up veneer is raw veneer that has been joined together to make larger pieces.The process is time-consuming
and requires great care, but is not difficult and requires no expensive tools or machinery.Veneers can be ordered
through some companies already laid up to any size, shape or design.
• Reconstituted veneer is made from fast-growing tropical species. Raw veneer is cut from a log and dyed if
necessary. Once dyed, the sheets are laminated together to
form a block.The block is then sliced so that the edges of the laminated veneer become the “grain” of the
39. • Wood onWood Also called 2-ply is a decorative wood veneer face with a utility grade wood backer applied at an
opposing direction to the face veneer.
• Patterns -There are a number of "patterns" common to veneered work.This refers to the way the veneers are laid up.A:
Book matched: where the veneers are opened from the flitch much like the pages of a book. B: Slip matched: where the
pieces are joined together in the order they come from the flitch and have the same face kept up. C: Radial matched:
where the veneer is cut into wedge shaped pieces and joined together. D: Diamond matched: where the pattern formed is
Advantages of using veneers Furniture made with wood veneer uses less wood than the same piece of furniture made
with solid wood. Some projects built using wood veneer would not be possible to construct using solid lumber, owing to
expansion and contraction caused by fluctuation of temperature and humidity.