Timber

TIMBER

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

CLASSIFICATION OF TREES

CONIFERS – Soft woods

DECIDUOUS – Hard woods

ENDOGENOUSEXOGENOUS

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.

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

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

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.

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.

Uses of timber

Frame work

Shuttering

Structural members

Staircases

Skirting

Doors/windows

Flooring boards

Cabinets/Shelves

Outdoor Sheds, Patios, Porches, Decks, etc.

Preservative treatment of wood in marine environment

Column Bases

Platform construction

Bearing

connections

PLYWOOD

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.

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.

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.

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

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

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,

Questions…???