4.2b Timber
Nature and Aims of Design
Nature of Design
Timber is a major building material that is renewable and uses the Sun’s energy to renew itself in a continuous cycle. While timber manufacture uses less energy and results in less air and water pollution than steel or concrete, consideration needs to be given to deforestation and the potential negative environmental impact the use of timber can have on communities and wildlife. (3.6)
Aims
Aim 9: Designers have great influence over the materials that they specify for products. The move towards using timber from sustainably managed forestry gives consumers confidence that rare species found in rainforests have an opportunity to recover.
Guidance
As DP Design Technology student you should:
Characteristics of natural timber: hardwood and softwood
Characteristics of man-made timbers
Treating and finishing timbers
Recovery and disposal of timbers
Guidance:
Characteristics include tensile strength, resistance to damp environments, longevity, aesthetic properties
Design contexts in which different timbers would be used
Concepts and Principles
There are two types of timber: Softwood and Hardwood.
Each of type of wood has different structures, which influences their respective physical and mechanical properties.
The grain of the timber influences the aesthetic and mechanical characteristics of the cut timber.
All naturally grown timber has a grain, which in addition to providing an aesthetic feature, also influences the mechanical properties of the wood.
Certain cuts of wood may be used in particular ways to take advantage of their mechanical properties.
In the examples at the right, notice how the different types of cuts influence the surface qualities of the wood.
Engineered Timber
Engineered timbers are made by glueing waste materials together to create a new material.
The process of producing engineered timber ensures that particular performance characteristics can be designed into the final product.
Treating and finishing timbers
Seasoning, treatments, and finishes can improve the aesthetic and performance characteristics of timber.
Seasoning
Timber, when harvested, has a high moisture content which makes it unsuitable for most applications. As such, it needs to be seasoned (dried out) in order for it to be in a form that has useful mechanical and physical properties.
The time it takes to season timber will depend on the type, age, local growing conditions, and the intended application. Seasoning can be as little as 1 year to 5 or more years, depending on the factors.
Treatment of timber
Various treatments can be applied to timber to improve its performance, particularly its degradation due to moisture or attack by fungus and insects. The most common are:
Protection from insects and fungus (dry rot). The main strategy is to apply chemicals that make the wood "poisonous" to these insects and fungi.
Protection from the weather. The wood is treated with a waterproofing chemical or other chemical that resists the absorption of water and prevents rotting.
Improving chemical resistance: Protect woods from corrosive chemicals such as acids
Finishing of timber
Various finishes can be applied to timber to alter its aesthetic qualities and provide protection from environmental factors
Stains color the wood to a desired tone. Many stains also provide some degree of UV protection.
Oils and waxes can alter the surface, from smooth to shiny, while also providing some protection from abrasion.
Recovery and Disposal of Timber
Wood is one of the most widely used materials in construction, furniture, housing, and manufacturing.
As sustainability has become increasingly important factor in design and manufacture, sustainable sources of raw timber and recycled wood waste are now more important to consumers.
Not all wood products are easily recyclable. Engineered timber, in particular, is challenging to recycle or reuse because of its high toxicity from binders (glue) used in its production, and the use of plastics in the case of particle board.
Waste timber is often chipped to make new products. These can include engineered timber, as well as wood chips used for landscape, animal bedding, and play areas.
Recycled timber, sometimes called reclaimed, is often prized for its aesthetic qualities. The aged wood, with its unique color and markings from use, can find numerous applications.
Sustainable Forest Management
Sustainable forests are carefully managed forests that ensure that trees that are cut are replaced by younger trees, while also preserving animal habitats and ecosystems, and allowing for leisure activities. The overall goal of a sustainable managed forest is to reduce the environmental impact of extracting the timber and to preserve as much as possible the natural environment and ecosystem.
The Food and Agriculture Organization (FAO) of the United Nations has adopted the following definition of Sustainably Managed Forests;
The stewardship and use of forests and forest lands in a way, and at a rate, that maintains their biodiversity, productivity, regeneration capacity, vitality and their potential to fulfill, now and in the future, relevant ecological, economic and social functions, at local, national, and global levels, and that does not cause damage to other ecosystems.
The Forest Stewardship Council (FSC) is one of several international bodies that certify the sustainability of timber resources.
Notice how the pattern of the grain is different depending on where it is cut from the tree.