is a natural fibre-reinforced polymer that has been used as a construction
material for many centuries.
All timbers are composed of a large number of close-packed tubular filaments of cellulose bonded together with an organic resin. In this sense they are composite materials with two different elements (with quite different properties) forming the material.
Trees grow by adding an annual ring below the protective outer layer (bark).
This "ring" is in fact a layer of cells which are large and plentiful during good growth conditions (spring, summer), but smaller and fewer in number during less favourable times (autumn and winter). As the tree grows, the inner cells age and die becoming harder and more compact. It then becomes heartwood which gives the tree its strength and support. This is the part of the tree that we use as a construction material.
Timber, once sawn into lengths, needs to be seasoned to lower the moisture content to around 10-20% prior to use. This can be performed in specially constructed huts, air seasoning, and takes a number of years. Kiln drying has now reduced the time taken for this process to about 10 weeks.
its natural state, timber falls into two categories: Softwood and Hardwood.
Softwood comes from coniferous trees which are distinguished by being
evergreen with needles and/or cones. These trees are relatively fast growing
and tend to be produced in countries which have a temperate climate ~
Northern Europe, Canada, USA. Their heartwood is porous and therefore
less dense with the result that softwoods tend to be easier to cut.
come from deciduous trees which shed their leaves annually. They tend
to grow more slowly than softwood and can be found in both temperate and
tropical climates ~ Europe, USA, Japan, Africa, Central and South America.
As a general rule, hardwoods are denser than softwoods and so tend to
be more difficult to shape and cut although there are some notable exceptions
such as balsa which is produced from a deciduous tree.
Additional information on timbers can be found on this link: http://www.rutlandwoodcraft.co.uk/timbers/
is available in a variety of market forms:
It is the grain in timber that gives it its strength but is also the cause of its greatest weakness. Wood has greater strength along the grain than across it ~ an important consideration during construction. Wood is also hydroscopic, absorbing and releasing moisture. When it gets damp it swells across the fibres of the grain increasing in size and causing the distortion known as warping. As a natural material it is also susceptible to natural defects such as knots. It is also prone to fungal attacks; dry and wet rot, as well as insect attacks; woodworm, termites etc.
problems can be overcome, to a certain extent, by manufactured boards.
Chipboard is made by compressing wood chips with resin such as urea formaldehyde. It is regularly veneered to increase its strength and to greatly improve its appearance. This enables it to be used for tables, shelving, work tops etc.
is available in a number of different forms:
are made by taking thin sheets or veneers and gluing them together under
high pressure and temperature. The most common example is plywood in which
each layer, or ply, has its grain at right angles to the next to make
the board stronger and more resistant to warp. Plywood is available in
a variety of thicknesses with a variety of plys (layers) and can have
special properties such as weatherproofing, waterproofing and marine-ply
which is suitable for marine use. Skin-ply makes the best use of the strength
to thickness ratio of plywood and allows curved surfaces to be formed.
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