Timber is one of the oldest building materials. It is available in most parts of the world and it is easy to handle and use. One disadvantage, however, is that most timber species react to environmental influences: they swell when they get damp and they can be attacked by insects. Over the last years tropical timbers have been very popular, especially in high end developments, as they react far less to dampness and in comparison to European timbers, hardly swell. New ways of treating local European timbers will allow us to drastically reduce the use of tropical timbers and to protect the rainforests.
The simplest technological way to minimize the shrinkage and swelling of timbers is the thermal treatment with hot plant oil (170 – 250⁰C). For two to three days the timber is treated in a heat process and as a result the cellular structure of the timber changes, such that the impact of water and damp can be reduced. After treatment the tendency to swell and shrink is reduced by half. The colour of the wood turns a deep and dark tone and bacteria and fungi can no longer feed on it.
Steaming of timber at 100⁰C can also lead to a deep and dark colour of the timber. This process however hardly changes the quality of the timber. A well known example is steamed copper beach.
If the top layer of the timber is charred, it can be protected against attacks from insects as well as rot. Charring is a traditional treatment for timbers and over the last years has been re-discovered in architectural applications.
Another way of treating soft woods for external us is acetylation. In this process the timbers react with acetic acid anhydride under heat and pressure. The capability to absorb water is reduced considerably which allows the timber to be used on the outside of buildings or for structures such as bridges.
Text supplied by Dr. Sascha Peter, Berlin, all rights reserved.