Timber

The structure of natural timberNatural timber is a natural composite material compromising cellulose fibres in a lignin matrix. The tensile strength of timber is greater along the grain (fibre) than across the grain (matrix).

“Cellulose Fibres in a Lignin Matrix”

Classifications of timber

Basically, trees break down into either Hardwoods or Softwoods.

All softwoods grow in temperate forests.

Hardwoods can be either temperate or tropical.

Where do woods come from?

Temperate regions (softwoods)

Where do woods come from?

Tropical regions (soft & hardwoods)

Softwoods originate from coniferous trees (also known as evergreens, or gymnosperms). Rather than losing their leaves all at one time, they tend to shed their leaves (which resemble and are called "needles") throughout the year and bear cones.

Hardwoods, on the other hand, come from deciduous trees which lose their leaves throughout the year and produce seeds covered with some kind of covering (sometimes a fruit or nut).

The classification of timber is based on the species it comes from, rather than its relative hardness or density.

Hardwoods include exotic deciduous species (such as ash, mahogany, oak, walnut and balsa) and Australian native evergreen species (such as jarrah, silky oak, brushbox, iron bark and spotted gum).

Softwoods come from coniferous species, such as true cedar, fir, pine and spruce.

Conifer treesConifer trees are referred to as softwoods. These grow only in temperate regions. They are often referred to as evergreens.

Characteristics of softwood treesCellulose content - 42% +/- 2%Lignin content - 28% +/- 3%Extractives content - 3% +/- 2%Fibre length - 2-6 mmCoarseness - 15-35 mg/100 mm

Deciduous treesDeciduous trees are referred to as hardwoods and that these grow in both temperate and tropical regions Characteristics of hardwood treesCellulose content - 45% +/- 2%Lignin content - 20% +/- 4%Extractives content - 5% +/- 3%Fibre length - 0.6-1.5 mmCoarseness - 5-10 mg/100m

Cellulose - consists of long, straight chains of glucose molecules. It forms the skeleton of the plant wall. These fibres are long, strong and translucent. Lignin - is a three dimensional phenolic polymer network. This "glue from hell" holds the cellulose fibres together and makes them rigid. Chemical pulping and bleaching processes selectively remove the lignin without significantly degrading the cellulose fibres. Extractives - account for 3(+/-2)% of softwoods. These materials include plant hormones, resin and fatty acids along with other substances that help the tree grow and resist disease and pests. These substances are highly toxic to aquatic life and account for much of the acute toxicity of pulp mill effluent.

Characteristics of softwood treesCellulose content - 42% +/- 2%Lignin content - 28% +/- 3%Extractives content - 3% +/- 2%Fibre length - 2-6 mmCoarseness - 15-35 mg/100 mm

Characteristics of hardwood treesCellulose content - 45% +/- 2%Lignin content - 20% +/- 4%Extractives content - 5% +/- 3%Fibre length - 0.6-1.5 mmCoarseness - 5-10 mg/100m

Density: higher density thereby harderLower density thereby most

varieties are softer than hardwood.

Found in regions:

Trees supplying hardwood are found throughout the world from the Boreal and Taiga forests of the North to the tropics and down into the far South, excluding Antarctica.

Found in the northern hemisphere.

Definition: Comes from deciduous trees that drop their leaves every year.

Trees that are conifer and have needles, and normally do not lose needles.

Properties: Broad leaves; enclosed nuts; higher density. Less dense; less durable; high calorific values.

Type: Mostly deciduous. Evergreen

Cost Expensive. Less expensive.

Examples of trees: Aspen, Poplar, Birch, Elm, Maple, etc. Pine, spruce, cedar, fir, larch,

Douglas-fir, etc.

Applications: Used for furniture but less frequently than softwood. Widely used as wood ware for building and furniture.

Hardwood Softwood

Renewable resources

Watch the following videos and discuss the issues relating to the consideration of timber as a renewable source.

Consider: time to reach maturity, soil erosion, greenhouse effect and extinction of species

• http://ibdtmlc2010.wikidot.com/4-3-timber

Composite timbers

Particle board, also known as chipboard, is an engineered wood product made from wood particles, such as wood chips, sawmill shavings, or even saw dust. This type of composite timber is generally cheaper, denser and more uniform than conventional wood and plywood. It is usually used as a substitution for them when appearance and strength are less important than cost.

Composite timbers

Plywood is an engineered board made from thin sheets of wood, called plies or wood veneers. Softwood plywood is usually made either of Douglas fir or spruce, pine, and fir (collectively known as Spruce-pine-fir), and is typically used for construction and industrial purposes. Hardwood plywood is used for some demanding end use.

Watch the video on how plywood is made

Comparing the two

Particle Board

Compare the two materials in the following table

Particle board Plywood

Composition

Hardness

Tensile strength

Resistance to damp environments

Aesthetic properties

Draw a cross-sectional view for each composite

Particle board Plywood

Selecting timberWhich timber you select will depend on the different structural and aesthetic design contexts.For example, timber for a building would require different characteristics than timber for furniture, or timber for a children’s toy.Softwood Plywood Hardwood Chipboard

Treating and Finishing wood

There are a number of reasons we treat of finish wood.

• To reduce attack by organisms• To reduce attack by chemicals• To enhance aesthetic properties• To modify other properties

Wood finishing refers to the process of embellishing and/or protecting the surface of a wooden material. The process starts with surface preparation, either by sanding by hand (typically using a sanding block or power sander), scraping, or planing. Imperfections or nail holes on the surface may be filled using wood putty or pores may be filled using wood filler. Often, the wood's colour is changed by staining, bleaching, ammonia fuming and a number of other techniques. Some woods such as pine or cherry do not take stain evenly, resulting in “blotching". To avoid blotching, a barrier coat such as shellac or “wood conditioner" is applied before the stain. Gel stains are also used to avoid blotching.

Wikipedia

Once the wood surface is prepared and stained, a number of coats of finish may be applied, often sanding between coats. Commonly used wood finishes include wax, shellac, drying oils (such as linseed oil or tung oil), lacquer, varnish, or paint. Other finishes called "oil finish" or "Danish Oil" are actually thin varnishes with a relatively large amount of oil and solvent. Water-based finishes can cause what is called "raising the grain" where surface fuzz emerges and requires sanding down.

Wikipedia

All measures that are taken to ensure a long life of wood fall under the definition wood preservation (timber treatment). Apart from structural wood preservation measures, there are a number of different (chemical) preservatives and processes (also known as timber treatment or lumber treatment) that can extend the life of wood, timber, wood structures or engineered wood. These generally increase the durability and resistance from being destroyed by insects or fungus.

Wikipedia

Visit this site to see detailed information on different timber treatments http://en.wikipedia.org/wiki/Wood_preservation

Timber for flooring

Hardwood floors come in many types, finishes and price ranges. The longevity of any type of flooring depends on how it's used and cared for. Hardwood and laminate floors are an attractive alternative to enhance the look of a home. They are the preferred alternative to carpet for anyone who suffers from allergies. Anyone who wishes to keep a check on microbes in the floor for the health of their children should consider either of these types of flooring as opposed to carpet.

Hardwood flooring comes in solid or engineered varieties. Both solid and engineered hardwood flooring is available finished or unfinished. Pre-finished hardwood floors are also known as factory finished. Unfinished hardwood floors may be referred to as job-site finished. Laminate flooring is an alternative to hardwood flooring but can have some drawbacks, including the fact that walking on it makes noise. Padding can be placed underneath to address this issue, however. Laminate flooring comes in three types: factory-glued, glueless and pre-glued. The glueless type is easily installed by snapping pieces together in grooves.

DurabilityOn scratch, stain, fade, moisture and impact resistance, laminate flooring rates better than hardwood flooring. However, some factory finishes of hardwood flooring are able to resist stains very well. Both types have comparable manufacturer's warranties. When hardwood flooring is properly cared for and maintained, it can last a lifetime. Laminate flooring can be expected to last less than 20 years. It is more scratch resistant than hardwood but it can be scratched by a heavy or jagged object that is dragged over it.

Laminate flooring can be used in an area of a house where the floors get wet from time to time, but it can be damaged if it gets very wet. Check the manufacturer's warranty for specific information about how laminate flooring will stand up to water and humidity.

AestheticsHardwood flooring looks much better than laminate flooring with a richer, warmer appearance. Laminate floor has a good look. Hardwood floors can be custom finished to an exact colour. Hardwood expands or contracts according to the amount of humidity. If hardwood flooring is exposed to too much direct sunlight, the colour can change. Laminate floors resist colour change from direct sunlight very well.

Maintenance and careLaminate flooring is easier to maintain but harder to repair than hardwood. All hardwood flooring, with the exception of acrylic impregnated hardwood, can be refinished. Laminate flooring cannot be. Hardwood floors should not be mopped or cleaned with water as this can cause permanent damage. Water also causes the hardwood flooring's finish to become dull. While hardwood flooring can be scratched, it can be easily repaired if it's only as deep as the finish. Laminate floors are easier to maintain because they don't need wax.