Identification of Timber | Characteristics of Good Timber | Properties of Timber

 

Identification of Timber

The timber identification technique is the ability to identify one wood species from one another.

1. Identifying Wood Based on Solidity -

Solidity is the characteristic of how solid the lumber is. Before we begin to identify the wood species, it is important to first confirm that it is actually solid wood or natural wood, and not manufactured by men. Here are some ways to do that :

·       The end-grain of man-made or manufactured lumber is easily distinguishable from the end-grain of natural lumber.

·       Real wood has growth rings clearly visible on freshly sawn surfaces.

·       Veneered wood usually has repeating grain patterns.

·       Check if it is plastic painted or printed to give a wood-like appearance.

2. Timber Identification Based on Color -

Another quick and easy way of lumber identification is through its color and appearance. Here is how.

· Natural timber color: First of all, verify whether the color on the wood you're trying to identify is natural or not.

· Weathered wood: Mostly, wood gets darker with age. So, if you're trying to identity an aged/old wood, chances are the color would be darker (or occasionally lighter) than the original lumber color. The best way to confirm this is by sanding a corner of the wood item to unveil its original color.

3. Timber Identification Based on Weight & Hardness -

The weight of one wood species will almost always be different from the weight of other species. So, you can identify timber based on its dry weight, hardness and density.

· If possible, try to weigh the wood and then compare it to commonly known wood species based on weight.

· Measure the lumber length, width, and thickness, and calculate its density in order to figure out weight per unit volume.

· To get an idea of the wood hardness, try cutting a corner with your fingernail.

4. Oduor and Taste -

· Oduor occurs due to certain chemical deposits. It is more pronounced in heartwood than that of sapwood.

· Taste is closely related to oduor, sugar-pine derives its name from the sweet exudations found on wounds on the living trees.

CHARACTERISTICS OF GOOD TIMBER -

The principal characteristics of timber of concern are strength, durability and finished appearance.
1. Narrow annual rings, closer the rings greater is the strength.
2. Compact medullary rays.
3. Dark colour.
4. Uniform texture.
5. Sweet smell and a shining fresh cut surface.
6. When struck sonorous sound is produced.
7. Free from the defects in timber.
8. Heavy weight.

9. No woolliness at fresh cut surface.

FUNDAMENTAL ENGINEERING PROPERTIES OF TIMBER -

Properties of Timber -

The quality of timber must be ensured before using it for a purpose. The quality can be ensured by investigating the properties of timber. Here we have discussed both physical and mechanical properties of timber which affects timber quality.

Followings are the physical and mechanical properties of timber:

1. Colour
2. Appearance
3. Hardness
4. Specific Gravity
5. Moisture Content
6. Grain
7. Shrinkage and Swelling
8. Strength
9. Density
10. Toughness
11. Elasticity
12. Warping
13. Durability
14. Defectless
15. Workability
16. Soundness
17. Free of abrasion

Colour -

Color is a uniform property by which most trees are characterized as they show variation from tree to tree. Light color indicates weak timber. For example, freshly cut teak, Deodar, and Walnut have a golden yellow, whitish and dark brown shades respectively.

Appearance -

Smell is a good property as timbers for few plants as they can be identified by their characteristic aroma. Fresh cut timbers have a good smell. For example, resinous smell from pine.

Hardness -

For the resistance of any kind of damage, hardness is an obvious property. It is defined and measured as resistance to indentation and resistance to scratching.

Specific Gravity -

Variation of timber in specific gravity (0.3-0.9) is found. It depends on pores present inside timber. The specific gravity of this light material is less than that of water (<1). But in case of compact wood where pores are almost absent and become heavier, their specific gravity increases up to 1.5. The specific gravity of wood is approximately equal for all species and averages 1.54.

Moisture Content -

Timbers are hygroscopic and gain water from nature (atmosphere). The absorption of water or dehydration depends on atmospheric humidity. If timbers moisture content is high that means the timber quality is low. Water content is the risk of fungal attack.

Grain -

Several types of grain arrangement found. On the grain structure quality of timber varies. Grains remain closely related.

Straight grain: Arrangement of vascular tissue (xylem and phloem) is important which grow parallel to the length of the timber that is termed as straight grain.

Coarse grain: vascular tissue and fibre arranged broadly and widely.

Interlocked grain: Instead of parallel arrangement twisted, a spiral arrangement may be found.

Shrinkage and Swelling -

The percentage of shrinkage and swelling varies from plant to plant. Some give higher percentage after drying. Shrinkage starts when cell walls of timber start to release water. In moisture atmosphere timber swells when cell walls absorb water. Good quality timbers swell less. Timbers having thicker wall swell more than a thinner one.

Strength -

Best quality timbers have the highest strength. Strength means capable to bear loads. Anisotropic material like timber has different structure at the different portion. So, the strength of timber is different at different points. Grain structure determines the strength of the timber. Some types of strength are

1.    Compressive strength: 500 kg/cm2 to 700 kg/cm2 load is enough to test timbers strength.

2.    Tensile strength: When timber is enough strong to the tensile force. If perpendicular force is made then timber is weaker. 500-2000 kg/cm2 is the range of tensile strength load.

3.    Transverse strength: Enough bending strength indicates good quality timber.

 

Density -

Timber having higher density have a thicker wall. All the mechanical properties of clear wood are related to its density, which varies directly with the apparent specific gravity.

 

Toughness -

Timber has to have the capability to bear shocks, jerk. Anti-bending and ant splitting characteristic is needed. Old timbers have annual rings which indicate their age is a good indicator.

Elasticity -

Another property elasticity means timber should attain its own shape after use. Because of this quality, it is used in sports bat.

Warping -

Environmental change with season can’t effect good quality timber.

Durability -

A good quality timber has the property to resist the attack the infection of fungus or other insects. This resistance quality makes timber better.    Wood is not affected by weak alkali solution but decays in an acid medium (pH < 4).

Defectless -

This property is gained if the timber is from a sound tree. A defectless tree is free from sap, shakes, and dead knots.

Workability -

A good timber is always easy to work on it. Easy to drag using saw on good timber. The finishing can be done well.

Soundness -

A good quality timber gives good sound.

Texture - 

The texture of good timber is fine and even.

Free of Abrasion -

Timber should not be damaged by the external environment. It has to gain the ability to protect its skin.