2. Lumber or timber is wood in any of its stages from felling through readiness for
use as structural material for construction.
The oldest construction material and still one of the most versatile
A natural material with inherent flaws and variability
In general, the quality of timber depends on the following factors;
1. Environmental conditions of the locality.
2. Maturity of the tree
3. Method of seasoning
4. Nature of soil
5. Process of preservation
6. Time of felling
4. Characteristic features of a good timber;
1. Appearance – Hard and shining.
2. Color – Preferably dark.
3. Defects – Free from dead knots, flaws, shakes, etc.
4. Durability – Resistance to fungi, insects, chemicals, physical and mechanical
agencies, acids, alkalis, etc.
5. Elasticity – A Good timber should regain the original shape when deforming
load is removed. (in case of bows, carriage shafts, sport goods, etc.)
6. Fibers – Straight fibers
7. Fire resistance – Wood is a bad conductor of heat. Heat conductivity
depends on porosity, moisture, surrounding temperature, bulk density, etc.
8. Hardness – Good timber should offer resistance when penetrated by another
body.
9. Smell – A good timber should have a sweet smell. Bad smell indicates decay.
10. Sound – Should give a clear ringing sound when struck.
11.Strength – Should work as a structure member like joist, beam, rafter.
12.Water permeability – should be low.
13.Weight – Sound and strong
14.Working condition – should be ease; capable of being easily planed or made
smooth.
5. Defects in timber
Defects occurring in timber are grouped into the following five divisions:
Conversion
During the process of converting timber to commercial form, the following
defects may occur:
Chip mark: this defect is indicated by the marks or signs placed by chips on the
finished surface of timber
Diagonal grain: improper sawing of timber
Torn grain: when a small depression is made on the finished surface due to falling
of some tool
Wane: presence of original rounded surface on the finished surface
Insects
Following are the insects which are usually responsible for the decay of timber:
Beetles
Marine borers (Barnea similis)
Termites
Carpenter ants
6. Defects due to fungi
Fungi attack timber when these conditions are all present:
1. The timber moisture content is above 25% on a dry-weight basis
2. The environment is warm enough
3. Air is present
Wood with less than 25% moisture (dry weight basis) can remain free of decay
for centuries. Similarly, wood submerged in water may not be attacked by fungi
if the amount of oxygen is inadequate.
Fungi timber defects:
1. Blue stain
2. Brown rot
3. Dry rot
4. Heart rot
5. Sap stain
6. Wet rot
7. White rot
7. Defects due to natural forces
1. Burls – Injury to tree in its young age.
2. Callus – Soft tissue of the skin
3. Chemical stain – Chemical action by any external agency
4. Coarse grain – Widening of annual rings
5. Dead wood – Indicated by light weight and reddish color
6. Druxiness – White decay spots caused by fungi.
7. Foxiness – Red and yellow spots due to poor ventilation
8. Knots – Breakage in wood fibers
9. Rind galls – Abnormal growth leading to curved swellings on the body of tree.
10. Shakes – Cracks which separate the wood fibers
11. Twisted fibers – usually caused by fast blowing wind during the tree’s young
age.
12. Upsets – Ruptures in wood fibers caused by crushing or compression.
13. Water stain – The wood becomes discolored.
14. Wind cracks – shrinking of surface due to exposure to atmospheric agents.
8. Defects due to seasoning
1. Bow – Curvature formed in the direction of length
2. Case-hardening – Early drying and shrinkage of exposed surface.
3. Check – Crack separating the fibers of wood.
4. Collapse – Flattening of wood due to uneven shrinkage.
5. Cup – Curvature formed in the transverse direction of timber.
6. Honey-combing – radial and circular cracks formed in the interior portion.
7. Split – When a check extends from end to another.
8. Twist – Spiral distortion along the length.
9. Warp – bending of a piece of timber due to tension.
9.
10. Uses of timber
Frame work
Shuttering
Structural members
Staircases
Skirting
Doors/windows
Flooring boards
Cabinets/Shelves
Outdoor Sheds, Patios, Porches, Decks, etc.
25. Plywoods are boards made from thin layers
of wood or veneers.
It is flexible, inexpensive, workable, re-
usable, and can usually be locally
manufactured. Plywood is used instead of
plain wood because of its resistance to
cracking, shrinkage, and twisting/warping,
and its general high degree of strength.
Plywood layers (called veneers) are glued
together with adjacent plies having
their grain at right angles to each other for
greater strength. There are usually an odd
number of plies so that the sheet is
balanced—this reduces warping. Because
of the way plywood is bonded (with grains
running against one another and with an
odd number of composite parts) it is very
hard to bend it perpendicular to the grain
direction.
26. Types of plywood
Softwood plywood
Hardwood plywood
Tropical plywood
Aircraft plywood
Decorative plywood
Flexible plywood
Marine plywood
Sizes
The most commonly used thickness range
is from 0.6 in.(1.6 cm.) to 3.0 in. (76 mm.).
The sizes of the most commonly used
plywood sheets are 4 ft.(1.2 m.) wide by
8 ft.(2.4 m.) or 3 ft. (0.9 m.) by 6 ft. (1.8 m.).
Width and length may vary in 1 ft.(0.3 m.)
in increments.
In US, the most commonly used size is: 4 ft
by 8 ft or 5 ft by 5 ft.
27. Advantages of plywood
1. As plies are placed at right angles to each other, the expansion and
shrinkage are comparatively very low.
2. They are available in a variety of decorative appearance.
3. They are available in large sizes.
4. They are elastic and hence they not liable to split or crack due to changes in
atmosphere.
5. They are light in weight.
6. They are not easily affected by moisture.
7. They are stronger than solid boards.
8. They are very easy to work and can be made to suit any design.
9. They do not split when nailed due to their cross grained structure.
10. They make use of timber in a quite economic way.
11. they possess uniform tensile strength in all directions.
28. Applications of plywood
Softwood plywood applications
Floors, walls and roofs in house constructions
Wind bracing panels
Fencing
Concrete shuttering panels
Ready-to-paint surfaces for constructions
29. Birch plywood applications
Panels in concrete form work systems
Floors, walls and roofs in transport vehicles
Container floors,
Floors subjected to heavy wear in various buildings
and factories,
Scaffolding materials
30. Fiberboard
Fiberboard is known as low density fiberboard is a type of engineered
wood product that is made out of wood fibers. Types of fiberboard (in order
of increasing density) include particle board, medium-density fiberboard,
and hardboard.
Standard Specification for Cellulosic Fiber Insulating Board, has many
benefits and is used in residential and commercial construction. Different
uses and applications include:
sound proofing/deadening,
structural sheathing,
low-slope roofing,
sound deadening flooring underlayment,
