Timber

Wood is a material category that concerns the fibrous tissue found in the stems and roots of tress. Materials within this category are organic and are therefore grown naturally over time as trees or shrubs. As it grows primary growth can be seen through the tips of the branches and roots, whilst secondary occurs internally as the cells within the tree divide

Each year/season a tree gains a new layer of wood, thickening the stem, producing a new growth ring which is visible as a cross-section. As the tree grows, lower branches break off as they die and form imperfections in the wood, creating knots. These impact the technical properties of the material when processed as they produce a weakness at this point which makes it prone to splitting. These can equally be used to enhance the aesthetic of a product with exposed wood grain. Knots are classified according to their form, size, soundness, and the firmness with which they are held in place.

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When a tree reaches the desired size, typically when the growth is less vigorous, it is felled and rough sawn for processing. Once felled, wood is known as timber, and is stored to allow some of the moisture content to evaporate reducing the weight for transport. The direction the wood is sawn in has an impact on the aesthetics & strength of the timber.

Plain/Slab Sawn is when the trunk is sawn across the diameter in parallel lines resulting in large elongated rings across the surface
Quarter Sawn is when the trunk is cut into 4 pieces around the centre axis and sawn into slabs given a straighter grain pattern
Rift Sawn is the most wasteful and expensive of the three but achieves a high material strength and unique linear grain

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Once sawn the timber is seasoned through drying either by heated kiln or naturally by air when stacked under shelter. This process makes the timber far stronger and less likely to rot over time. If it is dried too quickly through a heated process the timber can be weakened by case hardening, which results in the outside 'case' drying quicker than the centre creating shrinkage and causing the wood to warp (twist)

Once seasoned, timber can be treated with preservatives to extend its durability when used in outdoor applications to prevent decay and infestation. Tanalising is when timber is placed in a treatment tank and pressurised by vacuum pumping out the air. A preservative is poured into the tank and drawn into the fibres of the wood by the force of the pressure. Excess preservative is removed and the timber is then left to dry. Tanlised wood has a higher cost but is commonly used for outdoor applications such as fences & telegraph poles. The use of chemicals within this process has led to environmental concerns with recycled plastic commonly replacing its use in many areas

TYPES OF WOOD

Material Properties - Timber

Mr BILLINGTON