Timber Preservation. “Economic Necessity”

Press, Volume CII, Issue 30192, 25 July 1963, Page 16

Timber Preservation. “Economic Necessity”

The preservation of New Zealand's best non-durable timbers had become an economic necessity, said Mr R. D. Evison. a structural engineer, of Wellington, in an address on timber preservation to members of the Canterbury branch of the New Zealand Institution of Engineers last night.

Mr Evison said that a large part of New Zealand’s native timbers were naturally durable species which could stand a great deal of abuse during milling, transport, and use. Until recent years, supplies had been adequate, but changing circumstances had necessitated the up-grading in durability of strong timbers which had previously been of little use, except as fuel. “Suitably treated, these timbers have equal or better durability than those they replace. Now. after a few years. preservative-treated timber is overtaking untreated timber, particularly for building use," Mr Evison said. The preservation of timber which is naturally subject to biological attack, by impregnation with toxic chemicals had only recently become important in New Zealand, although it had been practised overseas for many years, he said. “In many respects our supplies and uses of timber differ considerably from those of other countries and this has resulted in a timberpreservation industry which is peculiar to New Zealand.

He said the task of preparing dependable timber treatment specifications for New Zealand was complicated by a number of factors. Timber had large diversities between species, even between trees of the same species, but with different histories.

The penetration of timber by preservatives was also variable, whether identical or different methods or materials were used. Some non-durable timbers were in-

capable of impregnation by common methods Preservative treatment had to protect against attack by widelydiffering organisms, some of which were resistant to some preservatives in common and successful use. Mr Evison said New Zealand conditions differed in many respects from those in other timber-treating countries. involving the timbers themselves, common habits of use. and conditions of attack "Over the last 25 years New Zealand's scientific work on the subject has been extensive. and in some respects present local practice leads the world."

He said that about 32 per cent, of all sawn timber in New Zealand was now treated, in addition to a vast amount of round timber. Of the building timber treated, about three-quarters was exotic.

He said that all treated timber now sold in New Zealand was controlled by the Timber Preservation Authority, which had issued and administrated specifications which were mandatory and enforced by regulation.