TIMBER 1.0 What is Timber? Definition & Types of Timber & Lumber 1.1 What is Timber? Timber is a type of wood which has been processed into beams and planks. It is also known as “lumber” in US and Canada. Basically, timber or Lumber is a wood or firewood of growing trees. Any wood capable of yielding a minimum dimensional size can be termed as a timber or lumber. It is a stage in the process of wood production. Timbers are used for the structural purpose. Those woods which are adapted for building purposes are timbers. Finished timber is supplied in standard sizes for the industry. Timber is used for building houses and making furniture. There is high demand for timber as a building material. From building construction to furniture making, timbers have numerous uses. These uses have made timber an important building material. 1.2 Types of Timber and Lumber Timber can be divided into two categories – hardwoods and softwoods. There are many types of timber under these two categories. They are * Bamboo * Birch * Cedar * Cherry * Cross-laminated * Glulam * Green timber * Lime * Mahogany * Oak * Pine * Plywood * Sapele wood * Tulipwood 1 * Walnut * Wood ash * Spruce * Fir 2.0 Properties of Timber - Qualities of Good Timber Wood 2.1 Properties of Timber The quality of timber must be ensured before using it for a purpose. The quality can b 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: * Colour * Appearance * Hardness * Specific Gravity * Moisture Content * Grain * Shrinkage and Swelling * Strength * Density * Toughness * Elasticity * Warping * Durability * Defectless * Workability * Soundness * Free of abrasion While selecting timbers for use, one must check these properties to ensure the quality. At the same time, it is also essential to ensure that the timber is defectless.. 2 These properties are briefly discussed below: 2.1.1 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. 2.1.2 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. 2.1.3 Hardness For the resistance of any kind of damage, hardness is an obvious property. 2.1.4 Specific Gravity Variation of umber 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. 2.1.5 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. 2.1.6 Grain Several types of grain arrangement found. On the grain structure quality of timber varies. Grains remain closely related. 1. 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. 3 2. Coarse grain: vascular tissue and fibre arranged broadly and widely. 3. Interlocked grain: Instead of parallel arrangement twisted, a spiral arrangement may be found. 2.1.7 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. 2.1.8 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 3. Transverse strength: Enough bending strength indicates good quality timber. 2.1.9 Density Timber having higher density have a thicker wall. An important property that quality of timber. Moisture content: Presence of defects: There may be some of the natural and artificial defects in timber such as cross-grain, knots, and shakes, etc. All of them decrease in the strength of the timber. 2.1.10 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. 4 2.1.11 Elasticity Another property elasticity means timber should attain its own shape after use. Because of this quality, it is used in sports bat. 2.1.12 Warping Environmental change with season can’t effect good quality timber. 2.1.13 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. 2.1.14 Defectless This property is gained if the timber is from a sound tree. A defectless tree is free from sap, shakes, and dead knots. To know more about timber defects read: Defects in Timber 2.1.15 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. 2.1.16 Soundness A good quality timber gives good sound. 2.1.17 Texture The texture of good timber is fine and even. 2.1.18 Free of Abrasion Timber should not be damaged by the external environment. It has to gain the ability to protect skin 3.0 Defects in Timber/Defect Types & Causes Timber is a natural product and every natural product has some imperfections. Timbers are not excluded from that. Most of the defects in timber cause weakness or others sorts 5 of difficulties. However, some defects can be beneficial for a specific type of work, for example, twisted wood is good for making a bowl out of timber. 3.1 Defects in Timber The followings are the five main types of defects in timber: 1. Defects due to Natural Forces 2. Defects due to Attack by Insects 3. Defects due to Fungi 4. Defects due to Defective Seasoning 5. Defects due to Defective Conversion These timber defects are briefly discussed below. 3.1.1 Defects in Timber due to Natural Forces a. Knots: Knots are the most common defects caused due to natural forces. During the growth of a tree, branches close to the ground or lower branches die. Bases of those branches remain in the tree as the trees grow. These bases may create imperfection known as knots. Types of Knots: Knots are of two types. i. Dead Knots: The remains of damaged branches after drying out they become loose and fall out. ii. Live Knots: They are sound and firm. If small, are not great of a defect. Live knots are usually not a problem as they remain firmly attached to the timber. But in dead knots, they are loosely attached and reduce strength. Knots decrease the strength of the wood and thus lower its value for structural uses, knots cause serious defects when the load is perpendicular to the grains. Image of Dead Knot and Live Knot Dead Knot and Live Knot. Source: woodexportchile.com 6 b. Twist: Twist in timber rotates the ends of the timber in opposite directions. The main reason behind this defect is twisting of the trees by the strong wing. twisting-of-the-trees-by the-strong-wind Twisting of the trees by the strong wind. Source:commons.wikimedia.org c. Shakes: Shakes are timber defects that occur around the annual ring or growth ring of a timber. In other words, cracks or splits in the woods are called shakes. It may or may not be a structural problem depending upon depth and use. The main problem is aesthetic. Where the appearance is important, shakes are undesirable. Types of Shakes: Shakes can be classified into three main categories: i. Star Shakes: This type of shake starts propagating from the bark towards the sapwood and sometimes even towards the heartwood along the lines of medullary rays. Cracks are wider on the outer edge or bark and narrower on the inside (usually sapwood, sometimes heartwood). The main reasons behind star shakes are extreme heat or frosting during the growth of the trees and rapid or uneven seasoning after cutting off the timber. Extreme heat or frost causes temperature difference, which causes shrinkage leading to the crack. ii. Cup and /or Ring Shakes: Cup shakes follow the annual growth ring. It is capable to separate the growth ring partially or completely. When the crack separately, it is called ring shakes. So all ring shakes are cup shakes, but all cup shakes are not a ring shape. Excessive frost action is the main reason for this type of crack. iii. Heart Shakes: Unlike star shakes, heart shakes starts propagating from the pith to the sapwood along the lines of medullary rays. Shrinkage of the interior part of the timber causes this crack. 7 d. Rind Galls: The meaning of rind is bark and gall is abnormal growth. So abnormal growth of the bark of the trees is called rind galls. Improper cutting of branches causes this abnormal growth. Wood from this portion of the timber lacks strength and desirable in structure. e. Upsets: Upsets in various wood indicate that the tree was subjected to crushing or compression. Improper felling of trees, heavy wind blowing during the young age of the tree these are the main reasons behind this type of defect. 3.1.2 Defects of Timber due to Attack by Insects Insects like beetles, termites or marine boars eat wood, make holes and weaken the strength of the wood. Beetles are small insects that make holes in almost all the sapwoods. The larvae make tunnels through the sapwood in all directs and turn wood into powder. Termites live in a colony. They are very fast in eating woods and making tunnels through it. Only a few good kinds of wood can withstand are the action of termites. Marine boars are found in salt water. Usually, they make tunnels in wood to take refuge or shelter. All kinds of wood or timber are vulnerable to this kind of insect. 3.1.3 Defects in Timber due to Attack by Fungi a. Stain: When fungi feed only on sapwood, where the food materials are stored, it causes a stain. Heartwood doesn’t contain these kinds of food materials and is not affected by it. Stain action causes color but does not affect the strength of the wood. b. Decay: Wood eating or wood destroying fungus is responsible for this type of defect in wood. This type of fungi breaks down the cell structure. Both sapwood and heartwood are affected by them. Considerable strength reduction occurs. 3.1.4 Defect in Timber due to Defective Seasoning 8 Faulty method of seasoning causes serious defects in woods. During seasoning of timber, exterior or surface layer of the timber dries before the interior surface. So, stress is developed due to the difference in shrinkage. In a perfect seasoning process, stress is kept minimum by controlling the shrinkage. Some of the defects resulting from defective seasoning are as follows: a. Bow: Curvature formed in direction of the length of the timber is called bow. b. Cup: Curvature formed in the transverse direction of the timber is called a cup. c. Check: Check is a kind of crack that separates fibers, but it doesn’t extend from one end to another. d. Split: Split is a special type of check that extends from one end to another. e. Honey Combing: Stress is developed in the heartwood during the drying process or seasoning. For these stresses, cracks are created in the form of honeycomb texture. 3.1.5 Defects of Timber due to Defective Conversion a. Boxed Heart: This term is applied to the timber which is sawn in a way that the pith or the center heart falls entirely within the surface throughout its length. b. Machine Burnt: Overheating is the main reason for this defect. c. Machine Notches: defective holding and pulling causes the defect. d. Miscut: erroneous cutting or sawing of wood causes this defect. Lack of experience in sawing and carelessness is the main reason for erroneous cutting. e. Imperfect Grain: Mismatch in grain alignment. 4.0 Uses of Wood A porous and fibrous hard structured plant stem which is the secondary xylem of the vascular tissue consisting of cellulose, hemicellulose and lignin can be defined as wood. It’s a supportive organ of woody plants forming the branches and stems give them a firm structure. 9 4.1 Uses of Wood in Different Sectors Wood is a plant part having multipurpose uses those are impossible to deny and difficult to note all in our daily life. From the ancient time wood is used by human and this continuation still remains in the modern civilization. A few of many uses of wood are mentioned below: 4.1.1 Construction and Fencing a. Home Construction: During the early periods, use of wood in domestic construction was a common scene and this is still followed in this twenty-first century. In different parts of the world in the making of houses, wood is used commonly like the flooring, frames of doors and windows for its strength and internment quality. e.g. Deodar (Cedrus deodara),walnut wood (Juglans sp) is used in Pakistan widely, teak (Tectona grandis) in South Asia and all over the world, Chir pine (Pinus roxburghii) etc. In Bangladesh during construction of buildings woods from mango (Mangifera indica), burflower three (Neolamarckia cadama) are used for casting and piling. b. Fencing and Decorating Gardens: In modern decoration system woods are also used for building the fencing and simple decoration for artificial gardening inside a home of on roofs. e.g. Cedar (Cedrus libani), redwood (Sequoia Semipervirens), Shorea sp, Acasia sp. 4.1.2 Household Uses a. Utensils: Utensils made up of wood instead of plastic and steel are a symbol of elegance which increases the charm and loveliness of the home corners. e.g. Black walnut (Juglans nigra) wood is used in the west for home utensils. b. Hand Tools: The handles of most common hand tools made of wood help as heat resistant when they are kitchenware used in an oven and closes the chance to shock while used on electricity. 10 4.1.3 Art Industry a. Artworks: For artworks such as statues, sculptures, carvings and making decorative objects woods are widely used. The frames of art board, color plate are also made from wood in many cases. e.g. Pine (Pinus sp), maple (Acer sp), cherry (Prunus sp) wood for framing work. b. Musical Instrument: The musical instruments such as Piano, violin, cello, drums, flute, guitar, double bass and a number of other music instruments material requires wood for making a perfect tune. e.g. Mahogany (Swietenia macrrophyila), maple, ash wood (Fraxinus sp) for guitars. 4.1.4 Sports Equipment Wooden Toys: These are preferred to plastic towards the health conscious people which were supposed as a fashion before. Plastic is nothing but the combination of chemicals which is hazardous to children’s health. Cricket, hockey, billiard, table tennis etc. Toys and sports equipment have long made use of wood for handles and main parts. e.g. Willow (Salix sp) wood for cricket, tennis bat; Mulberry (Morus sp) wood for hockey sticks. 4.1.5 Commercial Uses a. Furniture: At present, the marker for wooden furniture is very profitable. No one can deny the demand for wooden furniture as it is a sign of aristocracy since ancient time. e.g. Teak (Tectona grandis) wood is the best for making furniture. Some other woods from Mahogany (Swietenia macrophyiia), Shimul (Bombax ceiba), Sundari, Jackfruit (Artocarpus heterophyllus), Mango trees are used in South Asia for making different types of furniture. 11 b. Shipbuilding: Ships and rural fishing boats were made from wood. For constructing boats and ships wood is one of most important construction material. Hardwood and softwood were used in the past for ship industry. e.g. Teak, sgal (Shorea robusta), mango, Arjun (Terminalia arjuna) were frequently used in the past. Now Cypress (Cupressaceae sp), redwood (Sequoioideae sp), white oak (Quercus aIba) are water resistant and used for shipbuilding and boat building. Woods like Kauri (Agathis australis) is used for making the frames of ships. c. Fuel: Wood is an age-old source of energy all over the world. Before the exploration of gas, fuel was the main source we can also define as only one source of energy that people used by burning as woods were available in the forest easily. Generally, sticks, pellets, sawdust, and charcoal are used as an energy source from wood. Usually, woods from cheap plants are used in this sector. d. Stationary: Some stationeries like paper pencil are made of wood. Wood pulp is used for making paper. Wood is used for making pencils too. e.g. in the past Cyper papyrus trees were used to make paper. In Bangladesh woods from Keora (Sonneratia apetala), Bine (Avicennia alba), Sundari (Heritera fomes), Kakra (Bruguiera gymnorhyza), Geoa (Excoecaria agallocha) are used for making pulp of paper. Dhundal wood (Xylocarpus granatum) is used for pencil production. 5.0 Seasoning of Timber – Reason – Methods - Benefits Reduction of moisture content along with improving some qualities before the use of woods is called seasoning of timer. By seasoning, generally, the moisture is reduced to about 15% where new cut woods bear about 50%. 5.1 Reasons for Seasoning Seasoning of timber is done to fulfill some specific requirement. Followings are the reasons to perform timber seasoning, 12 1. To change and improve the properties of wood 2. To make a correct percentage of shrinking of woods 3. To make a confident use of woods 4. To reduce the adverse behavior of woods 5.2 Methods of Seasoning of Timber There are mainly two methods of seasoning of timber. These are: 1. Natural Seasoning 2. Artificial Seasoning Following tree diagram can be used to illustrate all the methods of timber seasoning. Seasoning of Timber Natural Seasoning Water Seasoning Air Seasoning Artificial Seasoning Seasoning by Boiling Chemical Seasoning Kiln Seasoning Progressive Kiln Seasoning Electrical Seasoning Compartmental Seasoning Detail explanation along with advantages and disadvantages of these methods of seasoning is discussed below. 5.2.1 Natural Seasoning Seasoning of woods or timbers using natural elements is called Natural Seasoning. e.g. water and air seasoning. (a) Water Seasoning: Removal of wood sap immersing logs into water flow is called water seasoning. It is carried out on the banks of the river while thicker ends are kept towards upstream. After that, the logs are allowed to dry. Disadvantage: It is time consuming such as 2 to 4 weeks generally. 13 (b) Air Seasoning: Exposing the wood to air for seasoning. At first, a platform is required that is built on the ground at 300mm height above the ground. Secondly, the arrangement of woods in layers. Air circulation is maintained between logs because it helps to reduce the moisture which is important for seasoning. The environment for this need to maintain some conditions. A clean, shady, dry, cool place is preferred. Sometimes logs are coated by the impermeable substance to reduce extreme moisture. To improve the quality oil coating, thick paint coating is maintained. To prevent fungal infection logs are treated with petrol or gasoline. Advantage of natural seasoning * Good quality of seasoned wood. * A large amount is convenient in this process. * Well-seasoned timber is formed. Disadvantage of natural seasoning * It’s a slow process. 5.2.2 Artificial Seasoning a. Seasoning by Boiling Seasoning by boiling wood logs in hot water is called seasoning by boiling. Dry is done after proper boiling. For a large amount of wood, it is done in an enclosed place where hot steam is passed. Advantages: * It takes a short amount of time. General, 3-4 hours is good enough. * Develops the strength and elasticity. Disadvantages: * It is serviceable basically for a small quantity of wood, not convenient for a large amount. 14 * The cost is high. b. Chemical Seasoning: Reduction of moisture using salt solution is called chemical seasoning. After the absorption of water by the solution logs are let to dry. Advantages: * It increases the strength of the timber. * It is less time-consuming. Disadvantages: * Chemical reagent can sometimes reduce strength * It can cause a problem in gluing or finishing or corrosion while using. c. Kiln Seasoning: Seasoning of wood by using a large chamber or oven where there is a good process for the circulation of hot air. Advantage: * Most effective and economic seasoning. Kiln seasoning can be done by 2 processes such as: i. Progressive Kiln Seasoning: Wood log is entered through the kiln and the temperature and humidity diferentials are maintained through the length of the kiln to maintain proper drying. ii. Compartmental Seasoning: Its maintained by enclosed container or buildings. Advantage: It accelerates the process because external energy is used. d. Electrical Seasoning: Dry wood is non-conductor of electricity while green timber is a conductor, so, can pass alternating current. Thus in this method alternating current is used for drying the cells of wood by creating heat. As electricity is used, it’s called electrical seasoning. 15 Advantage: * Using this method quick drying is obtained. A French electrical seasoning method is used to season overnight. Disadvantages: * The equipment required is very costly * It is an uneconomic process as a high rate of electricity is consumed. * During heating the cells of wood or timber they lose their strength and become weak. 5.3 Qualities Improved by Seasoning: By seasoning, some common known qualities are improved which are mentioned below: 1. Strength 2. Hardness 3. Durability 4. Weight 5. Painting and finishing 6. Gluing 7. Resistance to insect attack 8. Electrical resistance 9. Heat content 5.4 Precautions: Following precautions must be taken during seasoning of timber. * During seasoning, the moisture should be removed under an environment maintaining conditions. * Moisture should be extracted almost at an equal rate from all logs because differentiated dryness causes irregular shape. * Seasoned timber should be protected from exposure to the rain and excessively high humidity during air seasoning. 16 * During seasoning, a proper gap between logs should be maintained for easy and uniform air or water or hot air passing. 6.0 Difference Between Softwood and Hardwood. Softwood and hardwood are two different types of wood. To choose between these two types of wood one must know the differences between them. The main differences between Softwood and Hardwood are given below. Softwood VS Hardwood: Characteristics Source Softwood Hardwood Softwood is collected from Hardwood is obtained from conifer trees which are deciduous trees (loses evergreen having needle- leaves in autumn). They are shaped leaves. These are basically angiosperms. generally gymnosperms. Fibre Less dense, strait fiber is In case of hardwood, the found. fibers are quite close and dense. Resin Quality It is resinous wood contains Non-resinous woods have good and regular fragrant enough acid. smell. Weight Colour Lightweight and softer than Heavyweight and harder than hardwood. softwood. Softwood is light in colour. Normally these are dark coloured woods. Resistance to Fire Poorer than hardwood, burn at Better than softwood. Burn at a high rate. a very slow rate. 17 Weather If they are modified or treated Naturally resistant to whether resistance then these may become having a less environmental resistant to whether having an impact. environmental impact. Duration Less durable wood Hardwoods are highly durable and last for several decades. Ring Structure Distinct annual rings are found. The annual rings are not distinct. Medullary rays Indistinct medullary rays. Distinct medullary rays. Growth rate Softwood trees grow faster The growth rate of this type than hardwood trees. of trees is slower. Wood branching Creates more branch or shoots. Have fewer shoots. Tensile and shear Well tensile and comparatively Good tensile and shear strength weaker shear strength. strength. Cost Less expensive More expensive Uses Paper pulp, paper, solid wood Generally flooring and products, Woodwares like furniture. Also used for homes and cabins and also for papermaking. furniture. Workability Easier to carve. Difficult to curve. Example Black willow Salix nigra), Sugar maple (Acer Redwood (Sequoiodeae sp). saccharum), Eucalyptus (Eucalyptus globulus). 18