2. Conversion of Timber
• Before the wood is actually used in construction, certain operations
such as felling of trees, sawing them to logs and poles and beam etc,
becomes essential. All those process are Described below:
• Felling : Following two factors should be given due consideration before
felling of trees for use in as structural timber.
• (i) Maturity Trees become mature only after certain years when there
is good balance established between their heartwood and Sapwood. In
mature trees, growth rate is reduced considerably, and they have achieved
height & Grith of Standard Characteristics for their species. Only such
trees should be felled for use in conversion. Felling of young &
immature trees will give mostly sapwood, which will prove to be
uneconomical as they still grown to give greater volume of timber.
• To old trees will also give poor quality of Timber as their inner part
starts decaying with age. Hence the mature trees are best bargain for
construction timber.
4. Conversion of Timber
Time of Felling
• Spring and summer are always “bad
Season” for felling of trees. This is because
spring is the season of active growth for most
trees, Obviously the best time of felling trees
is autumn and beginning of winter.
6. Sawing of Timber
Sawing of Timber
• After their felling, trees are Usually cut
diametrically in convenient Length these are
Called logs.
• Collectively they are called Round Timber
• The Round table or logs are first air seasoned for
some period and then further cut into
transportable Parts.
• The main methods of sawing of the logs are :
through & through sawing and the selective
sawing.
8. Sawing of Timber
Through and Through Sawing
• In this method, the logs is cut lengthwise into pieces
of Suitable Dimension. One after another, without
giving any rotation during sawing, All the surface is
thus parallel.
Selective Sawing
• In this method, the log is rotated in different direction
after one or more successive cuts
• (i) Slash Cut: These are boards that have cut in a
direction tangential to the annular rings.
• (ii) Rift Cut :These are boards in which the annual
rings make an angle of more than 45 0 to the face
10. Quarter Sawing
Quarter Sawing
• It is a Process of Selective Sawing of the
Logs the main aim in this type of Sawing is
to Obtain Specially attractive Boards.
• In quarter Sawing boards are cut in such a
way that each board has one edge from the
centre of the log and the other edge from the
peripheral part of the log.
12. Seasoning of Wood
Seasoning of Wood
• A tree contains a lot of moisture in the standing condition.
The Mode of Occurrence of water in wood tissue is rather
complex and must be understood thoroughly.
• Whenever a freshly cut wood log is loaded for drying, it is
the free water that is lost first, Once the cell cavities are
empty, and drying is continued, then the water from the
cell walls will start moving out due to drying effect, It is the
only loss of water from the cell wall will start moving out due
to drying effect. It only the loss of water from the cell wall
that cause shrinkage in the wood.
14. Seasoning of Wood
• Similarly if a dry piece of wood is left out in a humid
atmosphere, wood will start absorbing moisture
Suppose the original moisture content of the dry
wood is only 6 % and the humidity in the moisture is
40 %the wood will go on absorbing moisture till its
moisture content is the same as that of the atmosphere
in which it is exposed this is called “equilibrium
Moisture Content” of the wood.
• When water is absorbed by the wood, it is the cell
walls that must be saturated before the cell cavities
are allowed to get any water. This is the reason doors
& windows made by wood show swelling effect during
rainy season.
16. Object of Seasoning
• By seasoning of wood is understood lowering its
moisture content to acceptable proportions before
putting it to any use.
• There are five major Objective of Seasoning
• First Reduction in weight
• If the moisture content of freshly cut logs is 50 %, it
means that 50 % weight of wood is due to water only. If
the timber logs are to be transported in the given
condition, it means we are paying quite huge amount of
money for transportation of Useless water stored in the
timber. Therefore log must be seasoned as near to the
felling place as possible before they are being transported.
18. Second Increase in Strength
Second Increase in Strength
• Moisture content in the cell walls and the cell
cavities decrease the strength of the timber.
Volume by Volume, there is much higher
quantity of wood tissue in dry wood than in
green wood It is the wood Tissue that bears all
the load water, weather in Cell walls or cell
cavities cannot bear any load. Hence other things
being same, higher the moisture content of a
variety of timber, lower will be the characteristic
strength.
20. Improvement in Workability
Third Improvement in Workability
• Timber has to be cut into smaller boards
and planks and other parts for various uses
Green timber will be more difficult to work
compare to seasoned timber.
• Further, it will be more economical to work
with dry seasoned timber because it will
involve less effort., less wastage of tools, and
better workmanship.
22. Freedom From Shrinkage Defects
Fourth freedom from shrinkage defects
• If the green timber is sawn into thin boards
and planks, it will get deformed within a
short time. This deformation described as
warping etc, will make the timber almost
useless for further working, Such defects will
not appear if the thin board are cut from
seasoned timber.
24. Longer life and Durability
Fifth Longer life and Durability
• Moisture in the timber invites a number of
micro-organisms and insect to thrive on its
sap. The fungi and Insect have a special
taste for cell sap. Hence the green timber is
attacked by these organisms quite easily. They
destroy the wood tissues to reach to the sap,
thus cutting short the durability of timber.
26. Seasoning
Seasoning
• Reduces much of the useless weight of timber;
• Increases its strength considerably
• Improve the workability of timber;
• Decrease the chances of development of
shrinkage defects, and
• Increase the life of timber, i.e. . It makes it
more durable.
27. Method of Seasoning
• At Present timber can be seasoned by a
number of methods
• They can be conveniently discussed under
two headings
• Natural Seasoning
• Artificial Seasoning
28. Natural Seasoning
Natural Seasoning
• This is an yet the most common process of seasoning used
throughout the world. In this process, timber sleepers, planks,
and scantling etc, cut from the wood logs are stalked in open air.
• These method requires careful preparation of
(a) Stack Ground
• It should be level, free from debris and on dry land it may be a few
cm below the ground.
(b) Stack Pillars
• These are constructed at regular intervals out of brick or masonry or
Concrete and may be of 50 cm height from the ground level
(c) Stack Proper
These are made of sawn timber shapes one stack should have timber of
one shape and same length and width.
30. Natural Seasoning
• The most essential consideration in making
such a stack is ensuring free circulation of
air around each part of wood placed in a
stack.
• It is also essential that the stack should be safe
from direct wind and direct scouring heat.
31. Natural Seasoning
Outline of stacking Arrangement
• The time taken for air seasoning depends on
climatic conditions and thickness of the timber.
It may take 1-4 years to bring down the
original moisture content of 30 % to a
desirable 16- 17 % level.
32. The Advantage Of Natural Seasoning Are:
The advantage of natural seasoning are:
• It is highly economical,
• It requires little supervision;
• It is applicable to thicker timber parts as thin section
• It is very Slow Process
• It keeps valuable Land and Timber blocked for longer
period and hence uneconomical
• Moisture Content cannot be brought below a certain
limit
• Seasoning is not always uniform in all the sections of
timber.
33. Water Seasoning
Water Seasoning
• This is the process of Natural seasoning that
gives good result with logs of freshly cut trees,
When the log are placed in running water, the
sap from the cell can be easily washed out. In
place of sap, the cell get filled with ordinary
water. When such logs are taken out and placed
for air seasoning. It takes comparatively less time
to become dry. Placing the log in water also
saves them from unequal shrinkage.
35. Artificial Seasoning
• This is the modern method of seasoning any type of
timber in short time. It involves drying the timber in a
specially designed kiln where there is perfect control
over temperature, humidity and air circulation.
Timber is stacked Properly
• In the Kiln keeping open spaces for air circulation.
The kiln is heated to low Initial temperature, once
slightly higher than the atmospheric temperature
outside.
• This initial low heat is essential to avoid cracking or
splitting of timber which would become certain if the
temperature is suddenly raised to higher rates. In that case
moisture in the deeper cell will be slow to move out.
37. Artificial Seasoning
• Once the timber has been at low heat and good
humidity for some time the temperature of kiln
is raised, humidity is reduced and air
circulation process of loss of moisture from the
deeper cells to the outer cell of the timber and
from there to outside the kiln starts
• During the heating process, all efforts are
made to maintain a uniform circulation of the
air so that all the part of timber receives same
amount of heat this aspect is most difficult one
in kiln and requires expert handling.
38. Chemical Seasoning
Chemical Seasoning
• In this method, the timber piece to be seasoned is
treated with a chemical solution like sodium
chloride, sodium nitrate or Urea.
• The essential quality of such a solution is that it
reduces the vapor pressure on the surface of
application. Once such a timber is exposed to
natural drying, it is the water from the inner cell
that moves to outer cell at lower vapor pressure.
The wood surface remain moist from the interior goes
on diffusing to the exterior. In other words chemical
seasoning enables the timber to dry first from inside.
40. Seasoning by Boiling
Seasoning by Boiling
• This is also a quick method of removing sap
from within the cells The timber to be seasoned
is immersed in water and water is heated to
boiling temperature. It is kept boiling for four to
five hours, the Sap is washed out by this process.
On placing in air such treated timber dries
quickly. But at the cost of Strength and
elasticity of the fiber, hence this method is also
rarely used.
42. Electrical Seasoning
Electrical Seasoning
• It is of theoretical importance only. Dry wood
is a non- conductor of electricity. But when a
high alternating current is passed through a
piece of green timber, heat generated is enough
to dry out the moisture of the cell which do
conduct some electricity. In this way the timber
pieced are dried quickly. This techniques involve
costly equipments and even the consumption of
electricity is so high that the process is
uneconomical.
44. Deterioration and Preservation
• While Using timber in construction, the engineer is always concerned with the
problem of decay and deterioration of timber with age
Causes of Decay
• (a) Fungi Decay of timber is mainly attributed to small plants and organisms that
live on and spread within the timber. A special type of organism called fungus starts
growing on the timber especially when it is placed on a moist ground or used in a
damp situation.
• Three main types of fungi are known to destroy the wood tissue
• The White Rot
• This type of fungus destroy the lignin part of the cell tissue living behind fluffy
cellulose part
• The Brown Rot
• Unlike White Rot, It eats up the cellulose part of the cell leaving behind brownish
lignin part
• The Blue Stain
• It is a fungus that lives on sugar and starch in the cell tissue. Such a fungus cause
staining or discoloration of the original board.
49. Deterioration and Preservation
Mold
• It is cotton like growth of fungus spread
over various parts on the surface of the
board. It may not spoil the inner portion of the
wood but its appearance on the surface is also
quite displeasing.
51. Insect
Insect
• A few type of insect are known to actually spoil huge
quantity of timber within a short time of few years.
The white ant so commonly found attacking wood
furniture in homes are the best example. The white
ant belong to a group of insect called termites. Other
insects that attack timber are pole borers and marine
borers or ship worms. The decay by termites is
encountered commonly in timber used in Building
Construction. The marine borer attack the wooden
base of ship in the sea.
53. Preservation of Timber
• Various methods have been used to preserve the
timber from decaying. The main objective of such
treatment is to ensure a longer trouble free life of
timber.
• There are three types of methods used for
preserving timber.
• Application of some chemical substance on the surface
of timber.
• Injection of preservatives in the body of the timber.
• Construction of protective Covering or shields around
used in construction.
55. Preservation of Timber
• A preservative may be defined as a chemical
compound that when applied makes the
timber ‘poisonous’ for insects and fungi
without effecting the structural properties of
timber.
56. Preservation of Timber
• All the wood preserving chemicals are classified into three groups;
The Oil Soluble Salts
• Such Compounds are soluble only in oils. The most commonly used oil
wood preservative, coal tar, creosote oil, belong to this category. It is
obtained by destructive distillation of coal.
The Water Soluble Salts
• Such Salts make an easy solution with water. There is an advantage in
it they can be easily dissolved and used., but there is an disadvantage too
they can be easily washed away if the timber happens to be in moist
condition.
• Among the water soluble salts include; zinc chloride, sodium fluoride,
sodium fluosilicates and compound of arsenic.
Volatile Base Salts
• Are those which make solutions with substances like petroleum, the
creosote petroleum blends are typical example of this category.
58. Method of Preservation
Method of Preservation
• Preservatives are used by different methods depending upon
the extent of preservation
Brush Application
• In this application timber is given one or two coats of the
preservative with the help of brush. This is used for
painting coal tar at the end of beams that are embedded in
the wall or base of poles.
Dipping Application The timber part to be treated is made to dip
in the preservative and kept immersed in it for various period
from a few hour to few day.
61. Method of Preservation
Open Tank Application
• In this method, the timber is kept immersed in a suitable
metallic tank of proper size till a proper saturation is
obtained. The tank containing timber is then heated at
about 70 to 80 0 C for several hours after this the timber is
allowed to cool within the tank in the presence of
preservative. In this way the timber may actually suck a lot
of preservative and ensures complete penetration.
• The Pressure Process This the best and commonly
applied method for preserving costly timber varieties. It
involves the Passage of preservative into the timber
under pressure and is achieved by either of the two
process.
63. The fuel Cell Process
The fuel Cell Process
• The timber is placed in a large steel cylinder acting
as a pressure vessel. Vacuum is first created and
maintained for about one hour or more after this,
coal tar cresolite oil or any suitable preservative ,
preheated to specified temperature is forced into the
cylinder under sufficient pressure. This is Continued
till the required quantity of preservative have been
introduced into the timber thereafter, pressure is
reduced and after giving some vacuum timber is taken
out.
65. Charring
Charring
• It is a common method used for preserving timber
poles and posts that are to be dug into the ground
The outer part in the lower end is charred
(incompletely Burnt) before insertion into the ground.
The charcoal layer so formed is an easy safeguard
against attacks by fungi.
Termite Shield
• The Base of Major timber may be preserved against
organic attack by constructing suitable barrier
between the timber and the ground The barrier of
proper design & shape are called termite shields.
67. Special Timber Product
Veneers
• A veneer is essentially a thin sheet of timber
with a thickness varying from 0.4 mm to 6
mm It is also called as a ply. From veneers a
number of wood product of specific
application can be prepared easily.
• Uses Veneers from starting point in the
manufacturing of plywood, laminated board
and battern board.
69. Special Timber Product
Ply Wood
• It is the most common type of processed wood containing thin
sheets glued to-gather In any type of plywood, the number of
plies is always odd and the grain of adjacent layers are
perpendicular to each other.
• Structure in the simplest type of plywood the board consist three
layers of plies arranged in such a manner :
• One ply lies in the middle and is referred as Central Ply
• One ply each lies on the either side of the central ply. One of this ply
is called face ply and the other as the back ply.
• Plywood panels may consist of any odd number of plies 5, 7, and 9
ply etc It is essential that plies holding identical position on either
side of the core ply must be of same thickness.
71. Special Timber Product
Uses of Plywood
• Plywood is used extensively in construction
and furniture making and many other fields.
Plywood is made in two types: The exterior
type and the Interior Type plywood. In the
former, a practical water proof glue is used for
bonding at the manufacturing stage. Such
plywood stable for external applications in
building construction e.g. Doors & Windows.
73. Laminated Timber
Laminated Timber
• It is a another type of Processed wood, It
consists of Suitably selected wood sheets or
veneers that have been glued together in such a
way that grains of all the sheets or lamination
are parallel longitudinally.
• Each lamination used in manufacturing of
laminated timber has a uniform thickness, not
exceeding 51 mm. Each lamination is itself
prepared by gluing together thin pieces of
timber having no defects in them.
75. • The laminated timber comes in wide variety
of shapes and appearances. It is
manufactured in three quantities Industrial,
Architectural, and Premium Grades
• In the Industrial Grade laminated timber,
small voids are allowed but one face is made
free from loose knots and holes. It is used in
Garages and Industrial Plants.
Laminated Timber
76. The Architectural Grade
• The Architectural Grade has a very smooth
external surface in which all knots have
been removed and voids so created filled
with clear wood tissue.
• The Premium Grade is manufactured with
great care and is used where highly appealing
and smooth external finish is required.
80. Fiberboards
Fiberboards
• These are made by pressing together fibrous material
such as fibres of wood, cane and even vegetable matter.
The fiber mass is first heated togeather and then pressed
hard in the hot state. On cooling, a rigid material of light
density and Good Utility is Obtained.
• The fiberboard are used as :
• Insulating Board
• Partition wall Panels
• Parts of flushing doors
• Finished flooring
82. Impreg and Compreg Timbers
Impreg and Compreg Timbers
• It is a class of processed timber products indicating use of an
advanced technology than plywood in the Impreg and Compreg
timber.
• In the impreg timber, for instances the veneer are immersed in
resins, commonly phenol formaldehyde at ordinary temperature
& Pressure. Once the tissue is saturated and the resin is set the
consolidated mass is cured at raised temperature, it is finally given
proper finishing treatment and is marked under the trade name
Sunmica
• The Compreg timber is a variety of impreg timber which is
prepared by curing resin impregnated timber at high
temperature and pressure. This type of curing results into a timber
of high density and strength that is quite durable.
85. Common Indian Timber
• More than 22 % of the total land in India is
under forest cover. Although there are more
than 100 species of wood in India only about a
dozen species are used in construction on large
scale
86. Common Indian Timber
(A) Softwood
Deodar
• Deodar botonical name cedar it is also known as god tree, and belongs
to the famous ‘Cedar’ Group of conifer trees
• Deodar is a very common tree in the N-W Himalayas The tree has tall and
straight trunk its height varies between 20 – 30 m and girth between 0.5 to
1.5 m the remain ever green
• Deodar timber is light colored and light weight material with a close
grained and long fiber texture. The timber is highly resinous and give odour
of resin
• The deodar tree is quite strong & durable.
• Uses
• Deodar tree is considered to be most valuable timber of the country. It
is extensively used in making railway sleepers in various part of the
building.
88. Kail
Kail
• It is botanical name is Pinus excelsa and
belongs to the pine group. Like Deodar, it is an
evergreen tree of Himalayas.
• The Kailwood is of light color and light weight
with a density of 480 kg/ cm 3. It is similar to
deodar in many properties but is considered
slightly inferior to that.
• Kail wood is used in building construction, for
sleeper for railways to sleepers for railway
lines and also for making furnitures.
90. Chir
Chir
• It is botanical name is Pinus longifolia. It is similar
to kail, and deodar in its appearance and grow
abundantly in Himalayas
• The Chirwood is highly resinous and very profused
knotted. It is light brown in color with a density of
about 560 kg/ cm3, being very much full of knots, the
chir timber is considered inferior to kail. And deodar.
• Uses Chir timber is Commonly used for making
packing cases and for interior work where not much
load is involved.
92. Simul
Simul
• Simul also referred as Cotton tree. It is common tall
tree of the plains of India. It grows naturally and
abundantly. The tree bears beautiful red flowers and
inferior quality cotton.
• Simul timber is of very light density. It is coarse
grained and of low strength . Hence it is not used as
structural timber in load bearing parts of the building.
However it is a commonly used wood for making
packing glass, toys and match boxes.
94. Hard Wood : Teak
Hard Wood : Teak
Teetona Grandis
• Teak yield one of the most favorable type of timber type
of the world. Its Sanskrit name is SAKA. Records show
that teak has been most widely used timber of India for
more than 2000 years.
• The teak is Usually a big tree with very big leaves, 70 –
90 cm in length. It has a spreading crown and four sided
branch lets. The teak tree wood is strong aromatic
odour, further teak wood is most durable teak wood
beam several centuries old but yet in perfect conditions
have been found from ancient India, Burma, and
Afghanistan.
96. Teak
• Teak wood is quite suitable for all types of
Structural work. Besides it is eminently
suitable for general wood work, such as ship
building, furniture making and in making
railway cars.
97. Shishum
• Shishum: Shishum is a beautiful tree of northern
and central India growing abundantly in plains up
to 2000 m above sea level. It is classed among the
broad leaved deciduous trees.
• Shishum timber is classed among the strongest timbers
of the world. It is very hard also. At the same time most
difficult to work with its density is 770 kg/ m3 , the
shisham sapwood is of light brown shade but the
Shishum heartwood is deep brown in shade.
• It has closed grained structure
• Very fine medullar rays
• Faint Annular rings
99. Babul
Babul
• It is one of the most common hardwoods of India growing in
almost all parts of the country. The tree is usually of medium
height and bears thrones, It has small leaves
• The timber of Babul is :
• Close Grained,
• Light red to brown in color
• Hard & tough in nature
• Resistant to wear
• The structural use of babul timber Include as beam and rafters,
frames & doors and window lintels
• In Common Usage babul timber finds its application for making
cartwheel and bodies, tools , handles, and other part of agricultural
implements
