In general, New Zealand timbers have poor durability; most people have had experience of borer in their houses. It is strange, therefore, that impregnation with chemical preservatives was not introduced earlier, but once commenced, this practice has led to a very spectacular development as the following figures for treated timber indicate: 1945, less than 10 million feet; 1955, seventy million feet; 1960, one hundred and sixty million feet.
Much of this increase has been in building timber; the main difference between the timber preservation industry here and elsewhere is the preponderance of building timber treated in New Zealand. Another important difference is the high standard in this country of preservative treatment. The success of the industry has been due to three things: the quality of basic research in New Zealand; the attitude of purveyors of preservative treatment; and, most important, the Timber Preservation Authority established in 1958. In fact, it is largely due to the work of the Authority that New Zealand is the only country in the world where the standard of preservation is so carefully controlled for the benefit of the industry and the public in general.
As a result of the successful treatment of the bulk of sapwood building timbers, greater attention is now being given to the protection of poles, posts, and heavy engineering timbers.
Preservatives used for building timbers are boron compounds and copper and zinc chrome arsenates, and for timber exposed to the elements, higher concentrations of metal chrome arsenates, creosote, and pentachlorophenol. Pressure impregnation (66 plants) is largely used except in the case of the bulk of boron impregnation, which is by the relatively simple diffusion process (82 plants). With regard to some creosote and pentachlorophenol treatments, the hot and cold bath method is adopted (five plants).
by Kennedy Mayo Harrow, M.AGR.SC., Plant Diseases Division, Department of Scientific and Industrial Research, Auckland.