Preservation

As they became familiar with local timbers, the early settlers were able to select suitable species for use as posts and poles from the abundance of mature trees then available. Where non-durable species had to be used they were often charred or given a superficial treatment of creosote or tar or even finely ground charcoal in linseed oil. Preservation on a commercial scale first began in the sleeper industry in Western Australia in the early 1900s, with the treatment of karri by the UK-developed Powellizing process, which involved boiling the sleepers in a solution of molasses containing some arsenic trioxide. Many were exported to the UK along with jarrah sleepers which, being more durable, were not required to have similar treatment. In the late 1920s the process was replaced by fluarizing, developed in the WA Forests Department[55] and which involved boiling with a mixture of sodium fluoride and either arsenic trioxide or sodium dinitrophenate, said to increase sleeper life two to three times. To protect poles and posts against ground decay open tank heating in creosote was also introduced to some extent early in this century but it was not until the 1930s that serious efforts were made to optimize it because of the growing scarcity of the more durable species and the waste involved in the then common practice of stripping the non-durable sapwood from poles intended for use in decay-prone situations.

When CSIR established a Division of Forest Products in 1928 preservation became one of its major activities. Some of the State forest services also became involved in preservation, as did a few public authorities concerned with the life of poles, sleepers and structural timbers. Overall there were two main thrusts in the research and development that started, one towards better protection against decay, termites and marine organisms, the other against Lyctus borer attack in sawn timber and plywood, a major problem for starch-containing sapwood, especially in New South Wales and Queensland.

In the 1930s CSIR started extensive field testing of the durability of Australian timbers treated in accordance with standard practices used in Europe and North America. The results served as the basis for further commercial development, as well as establishing the natural durabilities of the more common species. To achieve more effective and faster treatment of poles and posts it set up a pilot scale facility for pressure impregnation, a technique that had long been used in Europe, and co-operated with other interested groups to establish suitable conditions. The NSW Forests Commission built a small plant to apply this to local woods in 1944, but it was not until 1957 that a plant of any size was operating. This was built at Grafton, NSW by Hicksons (Aust.) Pty. Ltd., an offshoot of a UK company. Poles were vacuum-pressure impregnated with creosote at pressures up to 1400 kPa.

Australian Academy of Technological Sciences and Engineering