3B

• Wood is a natural renewable product from trees.
• Wood handbook is an excellent document describing the characteristics and properties of wood.
• Classification of Wood:

  1. Natural Wood
  2. Engineered Wood
• Trees is a woody plant that attains a height of at least 6m.
• There are over 600 species of trees.
• Natural Wood are made with a single piece of wood.
• Engineered Wood consists of multiple layers. This multi layers structure provides grater stability and resistance to moisture.
• Classification of Tree:

  1. Endogenous Trees
  2. Exogenous Tree
• Endogenous Trees grow with intertwined fibers.
• Exogenous Trees grow from the center out by adding concentric layers of wood around the central core.
• Deciduous Trees produce hardwoods. It generally shed their leaves at the end of each growing season.
• Conifers, also called as evergreens, have needlelike leaves and normally do not shed them at the end of each growing season. It produces softwood and widely used in construction.
• Classification within the tree family:

  1. Softwood
  2. Hardwood
• Hardwood grow slower and their timber is usually denser and stronger. It is used for furniture and decorative veneers.
• Softwood is softer, less dense, and easier to cut than hardwoods.
• Balsa is a very soft and lightweight wood.
• Example of Hardwood:

  1. Oak
  2. Walnut
  3. Maple

  Example of Softwood:

  1. Pines
  2. Cedars
  3. Spruces
• Timber is a type of wood which has been processes into beams and planks.
• Timber is also known as "lumber".
• Timber is any wood capable of yielding a minimum dimensional size.
• Characteristics of Good Timber:

  1. Narrow annual rings, closer the rings greater is the strength.
  2. Compact medullary rays.
  3. Dark color.
  4. Uniform texture.
  5. Sweet smell and a shining fresh cut surface.
  6. When struck, a sonorous sound is produced.
  7. Free from the defects in timber.
  8. Heavy weight.
  9. No woolliness at fresh cut surface.
• Seasoning is the process of reducing the moisture content (drying) of timber to prevent the timber from possible fermentation and making it suitable for use.
• Objects of Seasoning Wood:

  1. Reduce shrinkage and warping after placement in structure.
  2. Increase strength, durability and workability.
  3. Reduce its tendency to split and decay.
  4. Make it suitable for painting.
  5. Reduce its weight
• Methods of Seasoning:

  1. Natural or Air Seasoning
  2. Artificial Seasoning
• Methods under Artificial Seasoning:

  1. WATER SEASONING
  2. BOILING
  3. KILN SEASONING
  4. CHEMICAL OR SALT SEASONING
  5. ELECTRIC SEASONING
  6. MC. NEILL’S PROCESS
• Natural or Air Seasoning reduces the moisture content of the wood to 12-15 percent. The rate of drying is very slow and it is used very extensively in drying ties and the large size structural timbers.
• Artificial Seasoning: Timber logs are seasoned in a quick span of time.
• Water Seasoning is a quick process but elastic properties and strength of the wood are reduced. The logs of wood are kept completely immersed in running stream of water, with their larger ends pointing upstream.
• Boiling in water or exposing the wood to the action of steam spray is a very quick but expensive process of seasoning.
• Kiln Seasoning is adopted for rapid seasoning of timber on large scale to any moisture content. There is a little loss in strength of timber, usually lease than 10 percent. Wood is more thoroughly and evenly dried, thus reducing the hygroscopicity of the wood.
• Chemical or Salt Seasoning: The outer layers of timber are treated with a certain chemicals in aqueous solution with lower vapour pressures than that of water. The vapour pressure will reduce and a vapour pressure gradient is setup. Timber will exhibit fewer defects. Common salt or urea are generally used.
• Electric Seasoning: The logs are placed in such a way that their two ends touch the electrodes. Current is passed through the setup, being a bad conductor, wood resists the flow of current, generating heat in the process, which results in its drying.
• Mc. Neill's Process has no adverse effects. Best method although most expensive. The timber is stacked in a chamber with free air space (⅓ of its capacity) and containing products of combustion fuels in the fire place. Complete seasoning requires 15 to 60 days.
• Defects in Lumber:

  1. Knots
  2. Shakes
  3. Wane
  4. Sap Strake
  5. Bowing
  6. Checks and Splits
  7. Crooking
  8. Cupping
  9. Twisting
• Reaction Wood is abnormally woody tissue that forms in crooked stems or limbs. It creates internal stresses which can cause warping and longitudinal cracking.
• Pitch Pockets are well-defined openings between annual rings that contain free resin.
• Bark Pockets are small patches of bark embedded in the wood. These pockets form as a result of an injury to the tree, causing death to a small area of the cambium.
• Splits are lengthwise separations of the wood caused by either mishandling or seasoning.
• Raised, Loosened, or Fuzzy Grain may occur during cutting and dressing of lumber.
• Warp is a distortion of wood from the desired true plane.