Timber and its Types

Timber and its Types

1. Timber

Wood suitable for carpentry or other engineering works is called
timber. The word has timber has been derived from an old English
word timbrian. Natural durable wood is becoming scarce day by
day due to the growing demand for increasing housing activities.
The cost of selected wood like teak and bijasal has soared sky-high.
Presently, wood waste, i.e., sawdust, and wood shavings, are used
with an admixture of organic glues to manufacture fiberboards, fiber
slabs, etc. Besides, wood is also used for manufacturing other
products, i.e., organic acid, paper, cardboard. cellulose, resin, etc.

Structure of timber tree: -
The structure is of two types, macro and micro
Macrostructure: -
The macrostructure having pith, Heart wood, sap wood, cambium
layer, inner bark, outer bark and medullary rays.
PITH: Pith is the inner most portion of the tree, its size, shape and
colour varies from tree to tree. It is also called medulla; it is
responsible for the nutrition the plant at young age and after a long
time the pith dies.
HEART WOOD: It is annual inner rings which is outer portion of pith
and formed annually. it dead after formation of outer ring so dark in
colour and responsible for the stability of tree, due to hard property.
SAP WOOD: Sap wood is the outer annual rings and it is active part
which moves sap upward. Due to activeness it is light in colour and
indicates freshly made.
CAMBIUM LAYER: It gives sap to sap wood; it contains fresh shape
which is responsible for the life of tree. It is middle part of sap wood
and inner bark, if bark is removed then cambium fail to provide sap to
tree, and tree would be dead.

2. Microstructure: -
The wooden structure which is seen by microscope or any other
magnifying instrument is called microstructure because it is very small
in size which can’t be seen by naked eye. The dead and living part of
wood is seen and studies in the microstructure.

Time of Felling: -
Keeping in view the climatic conditions of the area and type of
trees, felling is normally done when the growth rate has reduced
considerably. Mid-winter is preferred for plains, whereas, midsummer
is the appropriate season for hilly areas.

Characteristics of Good Timber: -
1. Time of Felling
2. Nature of Soil
3. Maturity of the Tree
4. Method of Seasoning
5. Process of Preservation
Good timber should be from the heart of a sound tree with the sap
removed entirely. It should be dry, uniform in substance, well-
seasoned, straight-fiber and free from large or dead knots, flaws,
shakes, or blemishes of any kind.
A good timber should also possess low water permeability and
should be capable of withstanding weathering effects reasonably
well.

The decay of Timber: -
The decay of timber is caused by certain kinds of fungi and worms
like termites. The decay due to fungi is commonly known as rots,
which may be white or brown. The timber can be saved from decay
if the food material is poisoned by impregnating it with preservatives.

3. Situations which can accelerate the early decay of timber: -
• Alternate wet and dry conditions
• Bad stacking/ storage
• Improper seasoning
• Close contact with damp surfaces
• Complete non-removal of sapwood
• Non-application of appropriate preservative

Preservation of Timber: -
To preserve timber, various preservatives like- 1. Asco Treatment, 2.
Coal Tar, 3. Creosote Oil, 4. Chemical Salts, 5. Oil Paints, 6. Solignum
Paints, etc.
The best preservative is creosote oil. It is used for poles, railway
sleepers, etc. it's one of the best antiseptics. It should not be used in
the interior surfaces of dwelling houses, foodstuff godowns, and near
inflammable surfaces. The process of application is costly.
Coal Tar is a good preservative though less effective than creosote
oil. It being viscous, it does not deeply penetrate the wood. Except
for aluminum or yellow paint, no other paint can be applied over a
coal-tarred surface.

Defects in Timber: -
Defects in timber are due to several reasons, which affect its
strength, durability, and quality. They can either be natural or
artificial. The defects can be: -
1. Defects due to natural forces
2. Defects due to insects
3. Defects due to fungi
4. Defects due to conversion
5. Defects due to seasoning

4. Some of the Defects are Listed Below: -
Natural Defects: -
1. Knots
2. Shakes
3. Twisted Fibers
4. Upsets
5. Rindgalls

Defects due to Insects: -
1. Termites/ White Ants
2. Marine Borers/Ship Worms
3. Beetles
Defects Due to Fungi: -
1. Blue Stain (Forms Bluish stain, this fungus lives on starch)
2. White Rot (This fungus attacks lignin of the wood, white mass
formed)
3. Brown Rot (Wood shrinks, shows brown discoloration, cracks into
cubical pieces)
4. Dry Rot (In kitchens and toilets)
5. Heart Rot (Tree rots at the center, weaker structure)
6. Wet Rot (Greyish brown powder forms, alt. dry and wet
conditions)
7. Sap Stain (Fungus feeds on cell walls, causes stains in the sap)
Defects due to Conversion: -
1. Diagonal Grain
2. Torn Grain
3. Chip Mark
4. Wane
Defects due to Seasoning: -
1. Bow
2. Warp
3. Twist
4. Cup

5. 5. Case Hardening
6. Check
7. Collapse
8. Honeycombing
9. Radial Shakes
10. Split

Seasoning: -
Seasoning of timber is the process by which moisture content in the
timber is reduced to the required level. By reducing moisture
content, the strength, elasticity and durability properties are
developed. A well-seasoned timber has 15% moisture content in it.
Methods of Seasoning of Timber: -
• Natural
• Artificial

Natural Seasoning: -
Natural seasoning is the process in which timber is seasoned by
subjecting it to the natural elements such as air or water.
1. Water Seasoning: - Water seasoning is the process in
which timber is immersed in water flow which helps to
remove the sap present in the timber. It will take 2 to 4
weeks of time and after that, the timber is allowed to dry.
2. Air Seasoning: In the process of air seasoning timber logs
are arranged in layers in a shed. The arrangement is done
by maintaining some gap with the ground. The logs are
arranged in such a way that air is circulated freely
between logs. By the movement of air, the moisture
content in timber slowly reduces and seasoning occurs.

6. Artificial Seasoning of Timber: -
Natural seasoning gives good results but takes more time. So,
artificial seasoning of timber is developed nowadays. By artificial
seasoning, timber is seasoned within 4-5 days.
1. Seasoning by Boiling: - Seasoning of timber is also
achieved by boiling it in water for 3 to 4 hours. After
boiling timber is allowed to drying. For large quantity of
timber, boiling is difficult so, sometimes hot steam is
passed through timber logs in an enclosed room. It also
gives good results. The boiling or steaming process
develops the strength and elasticity of timber but
economically it is of heavier cost.
2. Chemical Seasoning: -In case of chemical seasoning,
timber is stored in a suitable salt solution for some time. The
salt solution used has the tendency to absorb water from
the timber. So, the moisture content is removed and then
timber is allowed to drying. It affects the strength of the
timber.
3. Kiln Seasoning: - In this method, timber is subjected to hot
air in the airtight chamber. The hot air circulates in
between the timber logs and reduces the moisture
content. The temperature inside the chamber is raised
with the help of heating coils. When the required
temperature is obtained moisture content and relative
humidity gets reduced and timber gets seasoned. Even
though it is a costly process it will give good results
strength-wise.
4. Electrical Seasoning: - In the method of electrical
seasoning timber is subjected to high-frequency
alternating currents. The resistance of timber against
electricity is measured at every interval of time. When the
required resistance is reached seasoning, the process is
stopped because the resistance of timber increases by
reducing moisture content in it. It is also called as a rapid
seasoning and it is uneconomical.

7. Preservation: -
Preservation of timber is carried out to increase the life of the timber.
Preservation is done using different types of preservatives. increasing
life makes the timber more durable and it can be used for longer
periods. Preservation also helps the timber to get rid of insects and
fungi etc. If preservation is not done, then the wood will be diseased
and damaged badly.
Properties of a good Preservative: -
• It should be effortlessly and cheaply available.
• It should not contain any harmful substances, gases etc.
• It should cover a larger area with a small quantity. Hence, it
should be economical.
• Decorative treatment or any surface treatment should be
allowed on timber after the application of preservative.
• Strength of timber should not be affected by the preservative.
• It should not contain any unpleasant smell.
• It should not get affected by light, heat, water etc.
• It should not get affected by fungi, insects etc. and should also
efficient to kill them.
• It should not generate flame when contacts with fire.
• It should not corrode metals when it makes contact with them.
• The depth of penetration of preservative in wood fibres should
be minimum 6mm to 25mm.

Conversion of Timber: -
The sawing up of logs to different forms for commercial purposes
such as planks, battens, balks, etc., is called a conversion. Due to
conversion, there will be loss of timber due to sawing which may go
up to as high as 40% in reduction of weight of the log. Probable loss
may be as follows: -

8. • Round Logs to Planks-40%
• Square Logs to Planks- 30%
• Round Logs to Scantlings-50%
• Square Logs to Scantlings- 40%
The following forms are available in the market: -
1. Log- trunk w/out the branches
2. Balk- squared timber
3. Board- 50 thick, 150 width
4. Planks- 200-380wide, 25-100 thick, 250-650cm length
5. Scantling-50x50-100x125
6. Pole/Spar-200mm dia

Special Timber Products: -
1. Veneers
2. Plywood
3. Fiber Boards
4. Impreg Boards
5. Compreg Timbers

Veneers: -
A veneer refers to a thin slice of wood, usually 4mm to 6mm. These
are manufactured by rotating a log of wood against a very sharp
knife of a rotary cutter or saw. Then they are sent to kilns for
removing moisture.
These are then used to make plywood, laminated boards, and
batten boards. Mahogany, Oak, Sisoo, Rosewood, and teak are
suitable for veneers.

9. Plywood: -
Made of veneers glued together. In any plywood, the number of
plies is odd and the grains of successive layers are at right angles to
each other. For ex- 5-ply, 7-ply, 9-ply, etc.
Glued together using animal or vegetable or synthetic resin glues.
Used for ceilings, doors, furniture, etc. it’s very common.

Fibre Boards: -
These are rigid boards manufactured by fibrous materials like
wooden fibres, cane, even vegetable matter. These are of the
types- insulating boards, medium hardboards, hardboards, super
hardboards, laminated boards.
The trade names of such locally available materials are- Euraka,
Indianite, Maonite, Nordex, Treetex, etc
Uses are-
• Insulating material for both heat and sound
• Flush doors and tabletops
• Partition wall panels
• Paving or Flooring material
• For internal finish of rooms, i.e., wall panelling and suspended
ceilings, etc.

Impreg Timber: -
Impreg timber is a timber covered fully or partly with resin. Thin layers
of wood or veneers are taken and dipped in resin solution. Generally
used resin is phenol formaldehyde. This is available in market with
different names such as sungloss, sunmica, Formica etc. Impreg
timber has good resistance against moisture, weathering, acids and
electricity. It is strong, durable and provides beautiful appearance. It
is used form making wood molds, furniture, decorative products etc.

10. Compreg Timber: -
It is similar to impreg timber but in this case, the timber is cured under
higher pressure conditions. So, it is more strengthened than impreg
timber. Its specific gravity lies from 1.30 to 1.35.

Other types of timber used are-
1. Block Board
2. Chip Board
3. Flush Door Shutters
4. Glulam