South African Wood Preservers Association (SAWPA)
SAWPA is an industry association which promotes the use of treated timber and treated timber products.
Understanding Timber Preservation.
A general introduction to the subject of wood technology and wood preservation. Knowledge of these fundamental factors can be of considerable assistance in gaining an appreciation of the value and importance of timber preservation and the selection of the most appropriate method of treatment. The growth of the Wood Preservation Industry has been one of the most important technical developments within the forest industry. The wide acceptance of preservation as an integral part of wood processing and utilisation has been a significant contribution to the use of what is the only structural raw material having a renewable and sustainable source of supply. There are timber structures still in existence after hundreds of years of service but there are fence posts which have rotted after only 18 months service.
This is due not only to a great variability in wood properties and our environment but also to the way in which the products are used. Wood suffers minor and gradual physical and chemical changes as a result of age. It is an organic material which can support the life of other organisms if the environment is suited to their growth and this, under certain conditions, leads to rapid breakdown of the wood. What are the circumstances in which wood is likely to be attacked by destructive agents and what measures should be taken to defeat them?
Most people can identify wood when they see it and can give names to the more familiar timbers in general use. However, much is taken for granted and relatively few may know timber in terms of a growing form of plant life or understand what structural variations produce the features characterising species which enable us to name them. The differences which exist between species are sufficient for us to realise that timber is a substance of greater diversity and character than materials such as steel and concrete. To enable the best use to be made of wood and to ensure the correct selection of the type best suited to any application, it is necessary to understand something of its structural form and characteristics and how these vary from species to species.
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South African Standards SANS 1288, SANS 457-2/3 and SANS 753/4 specify the marking requirements for any preservative treated product that claims to comply with the respective Standards. The following information must be contained in the marking: a unique plant identifier or trademark, product certification mark, SANS standard designation, a hazard class, date or year of manufacture of poles...
A tree trunk has three main zones; the bark, the sapwood and the heartwood. Trees are basically triangular in shape and they gain height by growing outwards and upwards. At the start of each growing season, a new layer is added to the outside of the wood so that every part of the tree gets bigger - roots, trunk, branches and twigs.
An important consideration when building with timber is predicting how long the structure will last. Whilst insects, decay or rotting organisms and marine borers can all attack wood, some timber species have the ability to resist attack better than others. The natural durability of a species to resist attack by wood destroying organisms is an indication of how long that timber will last when it is exposed to a defined set of exposure conditions without any additional preservative protection. The natural durability of timber species varies, even so within the wood from the same species of tree, depending on whether its sapwood or heartwood.