TIMBER

O Timber : Sources, Types, Classification,

Characteristics, Advantages & Uses.
O Growth & Structure of Exogenous Plants

O Defects in Timber

O Characteristics of Common Timber trees

O Seasoning of Timber :Air, Water, Kiln, Chemical,

Electrical & Boiling
O Preservation of Timber

O Properties and Uses of Bamboo

O Wood Based Products – Veneer, Plywood, Boards,

Laminated Boards etc.
TIMBER
•Is one of the important construction materials.
•Used as structural elements in buildings, widely for
doors, windows and partitions and find large use through
secondary wood products like plywood, particle boards
and laminated boards, etc.
•Wood Which is useful for engineering or Other
structural Purpose is called “Timber”
•Mostly uses timber – plywood,Posts et. in Formwork in
RCC,RBC etc.
•Both hard as well as soft woods are in use.
 TIMBER
• When tree has been cut down and its stem and branches are
roughly converted into pieces of suitable length, then it is
known as Rough Timber.
• When roughly converted timber is further sawn and
converted into commercialized the planks,battens, posts etc is
called converted Timber.
(Planks – board,plyboard,woodboards),
(battens-Partition, Roofing, something to hold)
O Mostly Timber used in load bearing
structure is called structural timber
H
Er. Prame H
Engineeri
H
Er. Pramesh Hada, Asst. Professor, civil
Engineering Department,nec
PROPERTIES OF TIMBER/WOOD
Physical Properties :
1. Density
- light — very light: density less than 550 kg/m3, eg.
bamboo
- moderately heavy: density 550 kg/m3 — 750 kg/m3, eg.
deodar
- heavy-very heavy: density greater than 750 kg/m3, eg. Sal

2. Bulk Density - Defined as the mass of many particles of the material

divided by the total volume they occupy.
- Depends on air voids present in wood.

3. Moisture Movement
- Wood is liable to shrink or swell with the movement of
moisture. (increase or decrease)
4. Shrinkage :
- Is a Reduction in linear and volumetric dimension due to
drying of moisture.
PROPERTIES OF TIMBER/WOOD
5. Swelling (Increase in size)
- It is increase in linear and volumetric dimension on
absorbing moisture.
6. Sound conductivity
- Has high Sound Conductivity
- Sound velocity in wood is greater than others.

7. Thermal Conductivity
- Has very low thermal conductivity.
- so uses for maintain heat temperature in rooms.
 MECHANICAL AND THERMAL PROPERTIES OF
TIMBER/WOOD:
O As wood is natural material there is different
mechanical properties for different wood
O Mechanical properties are governed by soil type,
climate and other factors.
O Properties affected by specific gravity, moisture
content, knots and other defects.
O Wood can’t resist fire and burnt easily.

O It will be better to take precautions to save timber

structure from thermal action
CHARACTERISTICS OF GOOD TIMBER
O Uniform color, strong, durable and workable
O Straight and compacted fibers

O Fresh cut surface : sweet smelling

O Struck: clear ringing sound

E
O Relatively heavier n

O Free from all types of defects and disease of timber like

knots.
O Planning surface: bright appearance with silky.

O Sawing: Cut with a saw - not clogging (clogging -Become

or cause to become obstructed)
O Firm adhesion of fibers and compacted medullary rays

O Well seasoned
Fibers in timber
H

Defects of Timber

Sawing
ADVANTAGES OF TIMBER
O availability:source and transportation
O strength: light weight and higher strength

O easy to handle and planed easily

O joining: simple
EE
O Repair and Modification: Easy nr .
g
i
O superior, thermal insulation, sound and electrical resistive
gh
O uses: furniture and decorative purpose DH

O strong and flexible

O corrosion resistance: excellent

O higher shock and impact strength .

O Quick and easy to build.

O Cheaper than other types of building materials.

O Easy to heat and cool depending on the weather.

O More eco-friendly than other materials

O Can last many years if proper maintenance is carried out.

USES OF TIMBER
It is mainly used for following categories of works
(i) It is used for construction purposes including building
construction, houseposts, beams, rafters, bridges, piles,
poles etc.
(ii) It is used for furniture and cabinet making.
(iii) Used for door and window frames.
iv) Uses for Formwork, scaffolding etc,
iv) It is also used for heavy packing cases such as
machinery and similar stores.
(v) It is used for manufacturing agricultural implements
and tool handles.
(vii) It is used for manufacturing veneers, plywoods,
boards etc.
HOUSEPOSTS

SCAFFOLDING
DISADVANTAGES OF TIMBER:
O Defects in timber can reduce the life of wood.
O Affected by relative humidity, fungi, insects.

O Modification of general arrangement drawings if based

on masonry construction
O Transportation and carriage access

O Exposure to weather before enclosed

O vulnerability to decay of timber when exposed to

excessive moisture.
O If left untreated, timber become water logged and
crack or chip.
O Timber is more susceptible to fire than other building
materials unless treated and maintained.
TYPES OF TIMBER/WOOD
O Wood is a product obtained from the tree.
O In simple classification of tree, it can be classified as:

1. Standing timber - if a tree is living then the timber is

termed as Standing Timber.
2. Rough timber - if a tree is fallen then the timber is
termed as Rough timber.
3. Converted timber - If a tree is modified into desired
size and shape then the timber is termed as Converted
timber.
on the basis of mode of growth , the types of trees are :
1. Endogenous Tree
2. Exogenous Tree
1. ENDOGENOUS TREE
O Trees grow in inward direction with the addition of fibrous (like
of jute) layer at tip portion, i.e the growth is longitudinal.
O Trees are hollow at the core and have flexible stem.
e.g- Bambo, coconut, Sugarcane etc.
O For construction purpose only bamboo can be used.
O Are very flexible due to which they are not generally used for
construction material.
2. EXOGENOUS TREE
O Trees increase in bulk by growing outwards and distinct
consecutive rings are formed in the horizontal section of such
trees.
O These rings are called annual rings, because one such ring added
every year, such trees grow bigger in diameter as well.
O Life of trees can be find by counting the annual rings.
e.g – Sisham, Sal, Pine etc.
O Timber from these suitable for construction purpose
These are further classified as
1. Deciduous tree 2. Coniferous tree
H
 EXOGENOUS TREE
Deciduous tree
O Are characterized by flat and broad
leaves which fall in autumn season and
new one appear in spring season
O Hard wood is obtained by such tree
which can be used for superior structural EE
nr .
g
inP
and engineering work. r
eera
i es
m
n
e.g – Sal, Sisham, Teak etc. gh
DH

Coniferous tree

epartment,nec
Professor, civil
ada, Asst.
OTrees are characterized by needle
shaped thin leaves which are evergreen
OTrees bear conical shaped fruits and
yield resins ( viscous substance )
O Soft variety of woods are obtained
OUsed is general constructional purpose
- e. g Pine, deodar etc.
H
DIFFERENCE BETWEEN HARD WOOD AND SOFT
WOOD (CHARACTERISTICS)

Aspects hard wood soft wood

Annual rings Indistinct Clearly distinct
Medullary rays Distinct indistinct
Color Dark Light
Strength Strong: tens, comp, shear Strong: direct pull
Weak: shear
Structure Non resinous Resinous and split easily

Weight Heavy Light

Uses Structural purpose Aesthetic and light structural
purpose
Sources Deciduous Conifers/evergreen trees
Branches Less branches More branches
Example Sal, teak, deodar, shisam Pine, chir, kai
STRUCTURE OF A EXOGENEOUS
H TREE (PU 2009,2010)

• Pith/Medulla/Core
•Heart wood
•Sap wood
•Cambium Layer
•Inner Bark
•Outer Bark
•Medullary rays
STRUCTURE OF A EXOGENEOUS TREE
Pith/ medulla/core:
O It is first formed portion of trees.
O It consist entirely cellular tissues and nourishes the plant in young
age.
O It is found as dead part of the trees incase of matured trees and
decayed.
Annual rings:
O Grows extra layer around the circumference of the trees per year
O Circular concentric rings
O Each rings indicates the age of tree in year
Heart wood:
O Annual rings around the pith at the innermost central portion of the
tree section
O Strong, durable and compact part of trees
O Darker in color
O Best part of trees in engineering views
O Imparts rigidity to the trees
O Doesn’t take active part in growth of trees
STRUCTURE OF A EXOGENEOUS TREE
Sap wood:
O Outer annual rings between heart wood and the cambium layer
O Light in color and weight as well
O Indicates recent growth and contains sap
(Sap = A watery solution of sugars, salts, and minerals that circulates through the vascular
system of a plant )
O Annual rings of sap wood are less sharply defined in comparison to heart wood
O Takes active part in growth of trees
Cambium layer:
O Thin layer of sap between sap wood and inner bark
O It indicates sap which has yet not been converted into sap wood
O If barks are removed and get exposed, the cell cease and death
Inner bark:
O Inner layer covering the cambium layer
O Protect cambium layer from any injury
Outer bark:
O A protective layer, outer skin covering the trees
O Contains cracks and fissures sometimes
O Consists of cells of wood fibers and is known as cortex
Medullary rays: (Pit rays )
O Radial fibers extending from pith to cambium layer
O Hold the annual rings of heart wood and sap wood together
H
MICROSTRUCTURE OF WOOD
O Structure of wood apparent only at great magnifications is called
microstructure.
O If study through microscope, it becomes evident that wood consists
of living and dead cell of various shape and sizes
O Living cell consists

➢ Membrane (consists cellular tissue and cellulose)

➢ Protoplasm (granular and transparent, viscous vegetables,

protein composed of carbon, hydrogen, oxygen, nitrogen and
sulphur)
➢ Sap (differ from protoplasm by presence of phosphorous and
shape is oval)

O Types of cell on the basis of their function:

➢ conductive cells

➢ mechanical cells

➢ storage cells
MICROSTRUCTURE OF WOOD

O Conductive cells: serves to transmit nutrients from

roots to the branches and leaves
O Mechanical Cells: these cells are elongated, thick
walled and having tightly interconnected narrow interior
cavities
- imparts strength to the wood
O Storage Cell: serves to store and transmit nutrients to
the living cells in horizontal direction and they are
usually located in the medullary rays
 H

Resinous wood
DEFECTS IN TIMBER (PU 08,09,10,12,13)
O Defects are either due to growing phases of tree or defect
occurring after cutting trees
O Defects reduce the usefulness of wood as aesthetic
appearance as well as strength
1. Heart Shake
- This defect usually occurs in over matured trees due to
shrinkage of heart wood
- These cracks are mostly confined to heart wood portion
and diminishing towards outward.
DEFECTS IN TIMBER
2. Star Shake
- It is confined in the outward portion
and diminishing towards center.
- It occurs due to frost action and strong
heat of sun.
- It is the most serious defect because it
tends to separate single log into small
pieces.

3. Radial Shake
- These are radial cracks extending from
centre towards bark .
- These are similar to star shake but are
irregular and numerous.
- It occurs due to drying of sap or
moisture .
 DEFECTS IN TIMBER
4. Cup or Ring Shake
- Is the separation of tissue along annual
rings
- If the shake is whole round the annual
ring then it is called ring shake and if it is
half way round the ring then it is called cup
shake.
- It is due to unequal seasoning and change
in humidity.

5. Rind Gall
- Is the curved irregular swelling on surface.
- Due to development of new sap layer on
wound left after branches have been
irregularly cut.
- New layer fails to unite with old one and
decay starts from that point
 DEFECTS IN TIMBER
6. Knots
- This defect occurs due to formation of annual rings at right
angles to surface and also due to twisting of fibers.
- The roots of the branches yet embedded(Enclosed firmly) by the
tissue and knots are formed
- Knots reduce the aesthetic value and effects tensile strength
- Knots may be round or oval shaped
DEFECTS IN TIMBER
7. Twisted fibers
- This defect occurs due to wind velocity constantly turning trees in
one direction only.

8. End Splits
- Occurs only at the ends of log due to exposed conditions during
seasoning.
- May be prevented by painting the ends of log or covering with
metallic cap.
DEFECTS IN TIMBER
9. Druxiness and Foxiness
(Druxiness is a term that is defined as a disease that is
found in timber or wood. It is caused or brought about by
a wound located in the layer known as the cambium
which is attacked by fungus.)
(Foxiness is caused due to poor ventilation during storage
or due to over maturity of the tree).

- These are stains or patches on the surface of timber

which destroy the appearance and may cause decay of
timber
- Stain may be in form of white patches or mottled
reddish colour.
(stains - A soiled or discolored appearance)
E H
H
SEASONING OF TIMBER:
O Wood is hygroscopic material, dry wood absorbs moisture from
surroundings
O Freshly cut wood may contains more than 50% water in the
form of sap and moisture
O After removal of such water from wood then it can be used in
diff. engineering works
O Thus drying process of timber is known as seasoning of timber
O Moisture must be extracted during seasoning under controlled
conditions as nearly as possible at a uniform rate from all parts
of the timber
O If the drying is irregular, the shrinkage of timber will also be
irregular and it will set up internal stresses between the fibers
O Moisture content in wood may be:
● Free moisture: present in cell cavities (major part)
● Bound moisture: present in cell wall ( associated with the body of
timber)
o Free moisture/ water evaporated first and the point at which cell
cavities no longer contain free water is known as fiber saturation point.
FOLLOWING ARE THE DIFFERENT OBJECTIVES OF
SEASONING:
O Timber to burn readily, if used as fuel
O Decreased the weight of timber: easy handling and
low cost
O Impart hardness, stiffness, strength, better electrical
resistance. (stiffness - hard to bend)
O To increase resisting power of timber against the
cause of defects
O To maintain the shape and size of the component of
the timber
O To make it fit for painting and other treatment

O For effectively gluing and joining

O To reduce the shrinkage, warping, twisting

(shrinkage - becoming less or smaller)
(Warping - Bend out of shape, as under pressure or from heat)
METHODS OF SEASONING OF TIMBER:
Natural seasoning
➢ Air seasoning/ drying
➢ Water seasoning
Artificial seasoning
Air seasoning:
Method used with the timber stacked in the open air. It
requires the following:
O Stacked stable and safely with horizontal spacing of at
least 25 mm.
O Ends of boards sealed by using a suitable sealer or cover
to prevent too rapid drying out via the end grain.
O The stack raised well clear of the ground, vegetation, etc
to provide good air circulation and free from rising damp,
frost, etc.
O Over head cover from effects of direct sunlight and
driving weather.
AIR SEASONING:

O This method is economical one

O Takes 2 to 4 years

O Covers more space

O No need of skilled labor

O Suitable for cut of sawn planks pieces of wood not for log
of wood
O Timber can stack either horizontally or vertically
 H

AIR SEASONING:
 H

AIR SEASONING:
 WATER SEASONING

O Log of wood is kept completely immerged in stream of

water
O Sap, sugar etc are leached out of wood and replaced by
water
O Then log is kept out of water after 2 to 4 weeks and
placed in air
O Quick process and also remove organic matters/
materials
O Elasticity may reduced and make timber brittle

O Boiling of timber in water is another rather quick

process
O Takes long time to be dried but less than air seasoning
ARTIFICIAL SEASONING:
OThis is quick process of seasoning and moisture content
can be controlled.
o Popular method of artificial seasoning is KILN
SEASONING.
Reason for carrying artificial seasoning are :
O Shrinkage, cracking and warping are minimized

O Drying is controlled and no chances for the attack of

fungi and insects
O Drying surface is even and uniform

O Reduced duration of seasoning

O Desired moisture content can be attainable

(shrinkage – becoming less or smaller)
(warping - Bend out of shape, as under pressure or from heat)
H
 KILN SEASONING:
O This process consists basically of introducing heat.
O May be directly, using natural gas and/or electricity or
indirectly, through steam-heated heat exchangers,
although solar energy is also possible.
O In the process, deliberate control of temperature,
relative humidity and air circulation is provided to give
conditions at various stages (moisture contents or
times) of drying the timber to achieve effective drying.
O Timber is stacked in chambers, called wood drying
kilns, which are fitted with equipment for manipulation
and control of the temperature and the relative
humidity of the drying air and its circulation rate
through the timber stack.
O Provides a means of overcoming the limitations imposed
by erratic(inconsistent) weather conditions.
O Almost all commercial timbers of the world are dried in
industrial kilns.
 KILN SEASONING:
O Advantages of conventional kiln drying include higher
throughput and better control of the final moisture content.
O Conventional kiln and solar drying both enable wood to be
dried to any moisture content regardless of weather
conditions.
O For most large-scale drying operations solar and
conventional kiln drying are more efficient than air drying.
O Compartment-type kilns are most commonly used in timber
companies.
O A compartment kiln is filled with a static batch of timber
through which air is circulated. In these types of kiln, the
timber remains stationary. Drying conditions are
successively varied from time to time in such a way that the
kilns provide control over the entire charge of timber being
dried.
O Method is well suited to the needs of timber companies,
which have to dry timbers of varied species and thickness.
O Kilns are used because the process speeds up seasoning and it
can be used to accurately control the moisture content of the
wood.
O Wood is carefully stacked inside the brick kiln.
O Water is heated and the resulting steam allowed to enter the
kiln, circulating inside and around the wood boards. Over
time, the amount of steam (humidity) is reduced until the
wood has the desired moisture content.
Compartmental kiln
O A compartment kiln is a single enclosed container or
building, etc.
O Timber is stacked as described above and the whole
stack is seasoned using a program of settings until the
whole stack is reduced to the moisture content
required.
Progressive:
O A progressive kiln has the stack on trolleys that
‘progressively’ travel through chambers that change
the conditions as it travels through the varying
atmospheres. (trolleys - An wheeled vehicle that runs on rails and is
propelled by electricity)
O The advantage of this system, although much larger,
has a continuous flow of seasoned timber coming off
line.
Solar kiln
O A solar kiln is a cross between kiln drying and air drying.
These kilns are generally a greenhouse with a high-
temperature fan and either vents or a condensing system.
Solar kilns are slower and variable due to the weather, but
are low cost.
Other seasoning of Timber are
Boiling or Steam seasoning
O Submersion in boiling water or the application of steam
speed the drying of wood. This method is said to cause less
shrinkage "...but it is expensive to use, and reduces the
strength and elasticity of the timber."
Chemical or salt seasoning
O Salt seasoning is the submersion of wood in a solution of
urea, sodium nitrate or sodium chloride, all of which act as
dehydrating agents. Then the wood is air dried.
Electrical seasoning
O Electrical seasoning involves running an electrical current
through the timber causing heat to build up drying the wood.
This method is expensive but is fast and uniform quality.
PRESERVATION OF TIMBER:
To prevent the probable defects of timber due to fungi, insects,
alternate heating and cooling timber must be preserved in order to
increase the life span of timber, make durable.
Following are the various methods of preservation :
Charring:
O Very old method, no preservatives are used

O Surface to be charred is kept wet for about half an hour and

burnt up to 15mm depth over a wood fire
O The charred portion is then cooled by water

O This burnt layer doesn’t affected by moisture, fungi etc

O Adopted for lower ends of posts for fencing, telephone etc

(Charring: Burn to charcoal )
Tarring : (coating)
• Timber surface is coated with hot coal tar with brushes
• Coal tar has unpleasant smell and appearance
• Coal tar makes timber unsuitable for painting
• Adopted for frames of doors and windows, rough timber work
etc
• Coal tar is fire-resistant.
( Tar - It can be produced from coal, wood, petroleum. It is black,
and a mixture of hydrocarbons and free carbon. )
 PRESERVATION OF TIMBER:
Painting:
O Paints are good preservatives
O Form thin layer in the surface of timber
O Thin surface acts as barrier for defective environmental factors

Creosoting:
O Timber surface coated with creosote oil

Engineering Department,nec
Er. Pramesh Hada, Asst. Professor, civil
O Creosote oil is obtained by distillation of tar (distillation - process of
purifying a liquid by boiling it and condensing its vapors)
Steps are:
O Timber are thoroughly seasoned and dried
O Placed well seasoned wood in air tight chamber
O Air is pumped out from chamber
O Creosote oil is then pumped under high pressure of 0.7-1.0N/mm2 and
temperature of about 500C
O After 1 to 2 hrs, when timber has sufficiently absorbed creosote oil, it
is taken out of chamber
O Creosote oil is antiseptic or it is poisonous to the wood-attacking fungi
O Creosote oil: black or brown liquid and weakly affected by water
O Unpleasant odour and having low wood-penetrating ability to the
extent of 1mm to 2mm only
O It produces undesirable color in timber
H
PRESERVATION OF TIMBER:
Abel’s process:
O Timber surface is cleaned and coated with a dilute
solution of sodium silicate
O Paste of slaked lime is then applied and finally, a
concentrated solution of silica soda is applied on the
timber surface
O This process is quite satisfactory in making the
timber fire- resistant
Fire proofing of timber:
O Timber can’t be made fire proof but some chemical
treatment may reduce the fire attack towards the
timber
O Soaking of timber in ammonium sulphate,
ammonium chloride, zinc chloride etc improves the
fire resisting capacity of timber.
H
WOOD BASED PRODUCTS
1. Veneers
O Veneering is the primary process of manufacturing
woods.
O Prepared by slicing and sawing of wood in thin sheets of
0.4mm to 6mm.
O Are of superior Quality.
O Used in manufacturing ply woods, battens, lamin
boards.
WOOD BASED PRODUCTS
2. Plywood
O Is a manufactured wood panel from the family of
manufactured boards (such as medium-density
fibreboard (MDF), particle board (chipboard), etc.) made
from thin sheets of wood veneer.
O Prepared by gluing together odd number of veneers with
grain direction of core block at right angle to adjacent
veneer or ply.
O Are used in making partition, furniture, ceiling, doors,
paneling wall, Formworks for concrete.
PLYWOOD H
3. BATTEN BOARD
O Is a solid block with core of sawn thin wood
O The Thickness of core is about 20mm to 25mm

O Total thickness of board is about 50mm

O Is Light and strong

O Do not crack or split easily

O Uses: partition wall, furniture, shutters, packing case

H
4. LAMIN BOARD
O Consist of core of strips each not exceeding 7 mm in
thickness.
O These strips are joined together with two face veneers.

O Lamin board are used for furniture, partition, doors,

windows, ceilings,etc.