Timber as a building material consists of uses, pros and cons. Classification of trees as exogeneous and endogeneous. Structure of tree. Processing of timber 4 stages - felling of trees, seasonong of timber, conversion of timber and preservation of timber. Characteristics of good timber and defects of timber. Industrial timbers

1. Timber as a Building
Material
- Ar. Satya Sravani Karuturi

2. Timber as a Building Material
• Timber is a naturally occurring material and is used for several
engineering purposes.
• The word timber refers to the wood used for construction. This
word derives from 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 and is applied to
the trees measuring not less than 600mm in girth or circumference
of the trunk.
• Living tree yielding good timber is called standing timber.
• After felling and separating branches, it is known as rough timber.
• when bark is removed and stem is roughly converted into pieces of
suitable length for transportation is known as log.
• After the log is seasoned and converted into commercial sizes like
planks, battens, posts and beams, it is known as converted timber.

3. Classification of Trees
Exogenous Trees :
• These trees grow outward and have
distinct consecutive annular rings in
their horizontal section. They can be
further divided into two types :
• a) Soft wood (conifers or evergreen
trees)– Chir, Deodar, fir, koil, pine,
spruce, etc.
• b) Hard Wood(deciduous) – Babul,
Mahogany, oak, sat, teak, etc.
• Lumber mostly used for engineering
purposes comes from Exogenous Trees.
Endogenous Trees :
• These trees grow inwards and fibrous
mass can be seen in the longitudinal
sections. Eg : Bamboo, Cane, Palm
etc. These trees have limited
engineering applications.

5. STRUCTURE OF A TREE

6. PROCESSING OF TIMBER
Following are the four stages for the processing of timber:
1) Felling of trees
2) Seasoning of timber
3) Conversion of timber
4) Preservation of timber
FELLING OF TREES:
To get timber, the trees are knocked down or cut down or caused to fall to the ground. This is known as the
felling of trees.
The important facts to be remembered in connection with felling of trees are as follows:
(i) 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 have attained maturity, the sap wood would be in excess
and timber obtained from such trees would not be durable and it will be in less quantity. On the other
hand, it is also not desirable to fell trees after they have fully matured as heart wood starts decaying after
maturity. The age of good trees for felling varies from 50 to 100 years.
(ii) Method of Felling: The trees should be felled by experienced persons. 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 tree.
(iii) Season for 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 trees in these seasons should be avoided.
• For hilly areas, the mid-summer would be the proper season for felling as there is heavy rainfall 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.

7. Seasoning of Timber
Seasoning is the process of reducing moisture content in a
freshly cut tree to the desired level.
Objects of seasoning:
1. increase the durability by protecting it from fungi,
insects and other causes related to moisture content;
2. impart hardness, stiffness, strength and resistance to
electric shocks;
3. maintain shape and size;
4. make it workable;
5. make it fit to receive painting;
6. make it suitable for gluing;
7. reduce the tendency of cracking and warping;
8. decrease weight and save transportation cost and
9. allow to burn easily, if used as fuel.
Methods of seasoning
Methods of seasoning may be broadly grouped into:
(a) Natural seasoning
(b) Artificial seasoning
Natural Seasoning: This type of seasoning may be in the form of:
(i) Air seasoning
(ii) Water seasoning
Artificial Seasoning: The various methods of artificial seasoning are:
(i) Boiling
(ii) Kiln seasoning
(iii) Chemical seasoning
(iv) Electrical seasoning

8. Advantages of natural seasoning :
• It requires low investment.
• It does not require skilled labour.
• It is ideally suited, to low and non-uniform market demand.
Disadvantages of Natural Seasoning:
• It needs larger space for seasoning.
• The process is very slow, usually takes 2-4 years.
• As the process depends on natural air, there is no control on it.
• Ends may dry fast and split. Interiors may remain moist while exteriors dry fast.
• The moisture content may not be brought down to the desired level.
• Chances of fungi and insect attack cannot be ruled out during the seasoning period.
Advantages of artificial seasoning:
• Drying is uniform, hence defect such as shrinkage, cracks and wrapping are minimum.
• Drying process is fast, hence economical.
• Moisture content can be reduced to the desired level.
• Chances of fungi and insects attack are low.
• Wood becomes more suitable for painting.
Disadvantages of artificial seasoning:
• It needs high investment.
• Skilled supervision is required.
• If demand is low and intermittent, it is uneconomical.
Natural Seasoning Artificial Seasoning

9. CONVERSION OF TIMBER
• The cutting up of timber to form planks, battens, etc. of required sizes by the saw is called a conversion.
• During conversion the allowance should be made for shrinkage, squaring, and planning. It is about 3 mm to 6
mm. The conversion should be carried out in such a way that there is minimum wastage of useful timber. The
wooden beams should be sawn in such a way that they do not contain pith in their cross-section.
• Strong pieces are obtained from timber when saw cuts are tangential to the annual rings and more or less
parallel to the direction of medullary rays.
The way that the log is cut will depend upon several factors, some of which are:
• The type and size of the sawing machine
• The size and diameter of the log.
• The condition of the log.
• The timber species
• Economy
• Timber may generally be sawn in one of the following ways:
• 1. Ordinary sawing
• 2. Radial sawing
• 3. Tangential sawing
• 4. Quarter sawing

10. Preservation of Timber
Except teak all other timber need treatment with preservation to protect it from attacks of fungi, insects and the weather.
Requirements of wood preservative:
• It should effectively resist fungi, insects and the action of weather
• It should possess good penetration and spread ability.
• It should be durable.
• It should give good appearance.
• It should not affect the strength of timber.
• It should be free from unpleasant smell.
• It should be non-inflammable.
• It should be cheap and easily available.
• It should cover large area with small quantity.
Widely used preservatives:
• Coal tar
• Solignum paints
• Chemical salt
• Creosote
• ASCU
Methods for Preservation of Timber:
Following are the six methods adopted for preservation of timber:
(i) Brushing
(ii) Charring
(iii) Dipping and steeping
(iv) Hot and cold open tank treatment
(v) Injecting under pressure
(vi) Spraying

11. Characteristics of Good Timber
A timber is said to be good based on the following characteristics :
• Durability - A good timber should be durable enough to resist the actions of chemical agents,
biological agents, physical agencies, etc.
• Strength - strength is the resistance against failure. A good timber should not fail easily and it
should be strong enough to take loads acting on it.
• Permeability - The permeability of timber should be less. A good timber should not absorb more
than 8 to 12% of water by its weight when placed in water.
• Hardness - Hardness is the resistance against penetration. Good timber should be hard and
workable. The hardness of timber depends upon its density and heartwood properties. Stronger is
the heartwood higher is the hardness of timber.
• Toughness - Toughness is the resistance against sudden shocks and vibrations. A good timber
should be tough enough to resist sudden impact loads and vibrations. A good tough timber is used
to make handles of different tools, parts of automobiles, etc.
• Elasticity - A good timber should be elastic. Elasticity is the property of regaining its original
shape after deformation causing loads are removed. A good elastic timber is used to make sports
items, shafts, bows, etc.
• Workability - Workability of timber is the ease with which it can cut into the required shape. A
good timber is easily workable. It should not damage or block the teeth of the saw during cutting.

12. • Weight - The timber should be heavy as much as it looks. A timber is said to be good if it weighs
heavy. Lightweight timbers are less in strength and unsound.
• Structure- A timber with uniform structure is said to be a good timber. The fibers of timber should
be straight and firm. The annual rings of timber should be closely located indicating the fact that the
tree is mature enough to use it for making timber products. The medullary rays should be hard and
compact. In general, an age of 50 to 100 years is considered a good age for felling of trees.
• Defects - A timber is said to be good when it is free from defects caused by natural forces such as
burls, knots, shakes, etc. and also it should be free from various fungal defects such as blue stain, dry
rot, wet rot. etc.
• Fire resistance - Fire-resistance of timber is very low. Of all the timber types, dense wood offers the
most resistance against fire but up to certain limit only. The thermal conductivity of timber depends
upon various factors such as moisture content, density, porosity, etc.
• Mechanical wear - Wooden floors, pavements, etc. made of timber are continuously subjected to
traffic loads. Hence, good timber should not deteriorate easily against mechanical wear or abrasion.
• Appearance - The appearance of a good timber should be shiny when it is freshly sawed. This
shining appearance is due to resinous matter present in the timber.
• Colour - The strength of timber can be estimated by looking at its color. Light color designates low
strength timber while dark color indicates high strength timber. Hence, dark-colored timber is
preferable for engineering works.
• Shape - The shape of timber should not be disturbed while cutting and seasoning. A bad timber may
bow or warp or split during conversion.
• Smell - The smell of a good timber is sweet. Bad or unpleasant smell indicates decayed timber.
• Sound - The velocity of sound in timber (hardwood) is approximately 12 times more than that in the
air. Hence, a good timber should produce clear ringing sound when struck. This is the reason why
many musical instruments are made of wood. A dull heavy sound designates decayed timber.
WARPED WOOD

13. DEFECTS IN TIMBER
The various defects likely to occur in timber may be grouped in the following divisions:
• Due to natural forces
• Due to attack by fungi
• Due to attack by insects
• Due to seasoning
• Due to conversion
Defects due to natural forces:
The following defects are caused by natural forces:
1. Knots
2. Shakes
3. Rind galls
4. Upsets
5. Twisted fibres
6. Wind cracks
7. Burls
8. Dead wood
9. Foxiness
Defects due to conversion:
1. Chip mark
2. Diagonal grain
3. Torn grain
4. Wane
Defects due to fungi:
1. Blue stain
2. Brown rot
3. Dry rot
4. Heart rot
5. Sap strain
6. Wet rot
7. White rot
Defects due to insects:
1. Beetles
2. Marine borers
3. Termites
1. Stain
2. Callus
3. Chemical stain
4. Coarse grain
5. Druxiness
6. Water stain
Defects due to seasoning:
1. Bow
2. Case – hardening
3. Check
4. Collapse
5. Cup
6. Honey – combing
7. Radial shakes
8. Split
9. Twist
10. Warp

14. Industrial Timbers
Industrial timber is nothing but timber product manufactured scientifically in factories. Because of its scientific nature, it is
stronger and durable than ordinary timber materials. It also contains desired shape and size.
Following are the different form of industrial timber:
• Veneers
• Plywood
• Fiber boards
• Impreg timbers
• Compreg timbers
• Hard boards
• Glulam
• Chip board
• Block board
• Flush door shutters

15. ASSIGNMENT
Answer the following questions along with neat diagrams.
1) Draw a neat cross section of stem of an exogenous tree and show
various components of it and describe them.
2) Discuss about various industrial timbers and their uses.
3) Enumerate the various defects in timber.
4) What is seasoning of timber? Why is it required? State various
methods of seasoning and explain them in detail.
5) Explain the process of felling of timber with a neat diagram.
6) What are the various sawing techniques by which timber is cut?
Explain them with diagrams.