Introduction

Timber is the one of the oldest structural materials

used by man. Temples and monuments built several centuries ago but which still remain in excellent condition show the durability and usefulness of timber Wood used for structural purpose is known as timber. In order to enhance and economize the utilization of wood, many wood-based products have been developed in a big way like veneers, plywood, hard board, etc.

Source of timber
The source of timber supply is the trees in the forest.
It is a part of plant life that thrives in many forms. Though trees are different from other forms of plant

life like herbs, they are basically of the same group, both in their structure and growth.

Classification of timber
The many species of timber used in construction engineering can be divided by two : Softwood Hardwood

Softwood
Produced either from softwood logs or a mixture of

both In structuring , there are a few of softwood that considered suitable to making structure component Usually softwood are used to make concrete mould or beam mould, known as formwork.

Hardwood
Usually got from good tree like Jati, Meranti, Kempas,

Cengal etc. Sometimes used to make furniture and also used for construction.

Product of Malaysian Timber

Foundation Beam Window frame Stairs beam Moulder / formwork Furniture Parquetry (floor)

- Bakau, Kempas - Cengal, Balau, Meranti - Kasai, Meranti, Nyatoh - Keledang, Simpoh - Damar, Keledang - Meranti, Getah - Balau, Tualang

Anatomy Of Timber
PITH This is the core of a tree which is hard Pith can also be called MEDULA. As the tree gets older this part tends to decay.

RAY Ray are produced from the pith. These rays contains tiny cells that is important in the growth of a tree.

Sapwood Sapwood contains both living and dead cells and functions primarily in the storage of food Heartwood Changes From Sapwood to Heartwood when it does not work as a sapwood anymore.

Bark There is the outer covering of a tree that is light and springy. Cambium A layer Full of cells situated inner from barks

Cross section of white oak tree trunk: (A) Outer bark (dry dead tissue), (B) Inner bark (living tissue), (C) Cambium, (D) Sapwood, (E) Heartwood, (F) Pith (G) Wood rays.

Characteristics Of Good Timber

Hardness

Wood Should not be bruised by an ordinary impact

Toughness

It must be difficult to split, hard to tear apart and will bend without breaking.
Elasticity

A good timber should regain its original shape after it is relived of loads.

 Strength

It must be able to resist heavy loads without breaking.

Durability

It should be able to resist that atmospheric effects, the attacks of fungi and worms.
Defects

A good timber should be free from any defect such as knots, shakes etc.

 Fibres And Structure

A good timber should have straight fibres. In a good timber, annual rings should be uniform in shape and colour.
Appearance & Colour

A freshly cut timber surface should present a shining appearance. Dark Colour.
Shape

A good timber should be capable of retaining its shape during the process of seasoning or conversion.

 Smell

A good timber should give a sweet smell.

Weight

Heavy weight timber is considered to be strong and sound. Denser timber is better.
Workability

A good timber should be easily workable.

Density

High density to withstand high stress.

Sizing
Softwood lumber is manufactured in length multiples

of 300 mm (1 ft) as specified in various grading rules. In practice, 600-mm (2-ft) multiples (in even numbers) are common for most construction lumber. Width of softwood lumber varies, commonly from standard 38 to 387 mm (nominal 2 to 16 in.).

The thickness of lumber can be generally categorized as follows:

Boardslumber less than standard 38 mm (nominal 2

in.) in thickness Dimensionlumber from standard 38 mm (nominal 2 in.)but not including, 114 mm (5 in.) in thickness Timberslumber standard 114 mm (nominal 5 in.) or more in thickness in least dimension

Methods of Sawing
3 basic methods:
1. Tangential/quarter Sawing
Timber is sawn tangentially to the annual rings. This

method is economical and involves less wastage.

Tangential/quarter Sawing

2. Radial Sawing Timber is sawn radially to the annual rings. This is an uneconomical way of sawing as it will involve more wastage.

3. Ordinary/plain and Flat Sawing Also known as the through and through cut method. This is a very economical way and the wastage is very minimum. However the shrinkage along the circumference is maximum.

Timber Products
Consists of a number of thin sheets or VENEERS of wood (odd number of plies) bonded together with an adhesive.
They are then pressed together in a large hydraulic presser.

Some examples of Timber Products: Plywood Wood fibre boards

Hardboards Medium boards Softboards

Particle boards (chipboards)

Glue laminated timber (glulam)

What are the effects of moisture in timber?

Definition:

Moisture content =
In trees, moisture content can range from about 30% to

more than 200% of the weight of wood substance. Weight, shrinkage, strength, and other properties depend upon the moisture content of wood.

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Moisture content of timber in service is greatly influenced

by the fact that wood is hygroscopic (tendency to attract water from a damp atmosphere and give upwater to a dry atmosphere). Consequentially, timber will adopt an equilibrium moisture content in a given environment, depending on the relative humidity of that environment. Variability of moisture content exists even within individual boards cut from the same tree. Timber becomes susceptible to fungal attacks at moisture contents in excess of 20 %.

Wood Seasoning
Seasoning is the controlled process of reducing the moisture content (MC) of the timber so that it is suitable for the environment and intended use. We need to reduce the MC of timber for the following reasons:
Every time the MC reduces the timber shrinks especially

tangentially. Consequently it will show fewer tendencies to warp, split or shake. Seasoned timber although lighter will be stronger and more reliable. The sap in timber is a food for fungi and wood parasites. Remove the sap and the wood will be less attractive to these dangers. For construction grade timber the timber must be below 20% MC to reduce the chances of Dry Rot and other fungi infestations. Dry well seasoned timber is stronger. Dry well seasoned timber is easier to work with and consequently safer especially machine working. Timber with higher moisture content is difficult to finish i.e. paint, varnish, etc.

Wood Seasoning 1. Air seasoning / air drying 2. Kiln seasoning / kiln drying
Both methods require the timber be stacked and separated to allow the full circulation flow of air, etc. around the stack.

Air drying
Is the drying of timber by exposing it to the air. The

technique of air drying consists mainly of making a stack of sawn timber (with the layers of boards separated by stickers) on raised foundations, in a clean, cool, dry and shady place. For successful air drying, a continuous and uniform flow of air throughout the pile of the timber needs to be arranged .

Seasoning
Air seasoning

Seasoning
Kiln seasoning

Kiln seasoning
There are two main methods used in artificial seasoning,

compartmental, and progressive. Both methods rely on the controlled environment to dry out the timber and require the following factors:
Forced air circulation by using large fans, blowers, etc. Heat of some form provided by piped steam. Humidity control provided by steam jets.

The amount and duration of air, heat and humidity again

depends on species, size, quantity, etc. Schedules are published for the various species to enable operators to select an appropriate drying environment.

Compartmental.
A compartment kiln is a single enclosed container or

building, etc. The timber is stacked as described above and the whole stack is seasoned using a programme of settings until the whole stack is reduced to the MC required.

Progressive.
A progressive kiln has the stack on trolleys that

progressively travel through chambers that change the conditions as it travels through the varying atmospheres. The advantage of this system, although much larger, has a continuous flow of seasoned timber coming off line.

Following are the advantages of Seasoning:

No risk of fungal decay
Reduces weight Improvement in Strength Properties Increase in Nail and screw holding capacity Improves Gluing capacity Helps in Preservative Treatment Wood exhibits better electrical and thermal Insulation

properties

PRESERVATION OF WOOD
Wood preservation means treating wood with solutions which make it poisonous to fungi, insects e.t.c

Common preservatives
Preservatives must be toxic to fungi and insects,

chemically stable, able to penetrate timber, and non aggressive to surrounding materials

TYPE OF PRESERVATIVE
Type 1 (Oil type)

- Coal tar creosol -with or without admixture

Type 2 (Organic solvent type)

-copper napthenate, zinc napthenate, benzene hexa-chloride and DDT (dichloro-diphenyl trichloroethane)

 Type 3 (Water borne) - toxic chemicals in water - zinc chloride, boric acid, copper chrome arsenic composition

Method of Applying Preservatives On Timber

Brush and spray Deluging, dipping, and steeping The hot and cold open tank method Pressure impregnation Painting (usually oil paints)

Methods of application

Double vacuum process

Type of preservative Tar oil preservatives

Properties A derivative of wood or coal

Action Prevents fungal and insect attacks

advantages Cheap, can be applied to timber with high moisture content

disadvantages Noticeable color and smell, makes the surface unsuitable for painting, creep into adjacent cement and plaster

Water born preservatives

Are salt based metals such as boron magnesium, sodium, copper-chromearsenate Contains organic solvents such as chloronaphthalenes

Prevents fungal and insect attacks

Cheap, non-creep, do not stain

Swells the timber, corrosion of metals in contact

Organic solvent preservatives

Penetrates deep into the timber

Non creeping, non staining and non corrosive to metals also non swelling and non corrosive to metals

Fire risk is in creased

Boron diffusion

Uses borate solution

Freshly felled timber is Cheap dipped in to borate solution which quickly diffuses into the wood

Highly toxic

Types of attacks on wood

Problems with wood Fungal attacks ( Wet rot and dry rot) Insect attacks Fire

Fungal attacks
Serpula lacrymans Coniophora puteana

Insect attacks

Fire

Fire retardants

Assignment
Explain these following methods for applying Preservatives

On Timber :
The hot and cold open tank method Pressure impregnation

Why is preservative treatment necessary for

timber Explain three main defects on timber