Timber specimens were impregnated with the organo-silicate tetraethyl orthosilicate (TEOS) in an effort to deposit hard silica granules and improve resistance to wood-borers. Trials were conducted against marine borers (teredinids and Limnoria), the termite Coptotermes acinaciformis, and the wood-boring beetle Lyctus brunneus. A 14-week laboratory bioassay against C. acinaciformis showed that treated Pinus radiata containing 16.7 wt.% silica was as readily attacked as untreated timber. However, a 3-year laboratory trial of treated Castanospermum australe showed that attack by L. brunneus was prevented by 10.3 wt.% silica, and reduced by 0.7 and 3.4 wt.% silica. A trial of wood treated with copper-chromium-arsenic followed by silicon was conducted in the sea at Townsville, Australia for 7 years. Double treatment with 6.7 or 19.2 wt.% silica prevented attack in P. radiata by teredinids, while for CCA alone some replicates failed. In the same trial, double-treated Corymbia maculata with lower silica retention failed. Silica granules may overwhelm the food and waste-sorting mechanisms in teredinids and lyctine larvae, whereas borers, requiring less intimate contact with granules (Limnoria and termites), or those that do not ingest wood for food (Sphaeroma and Martesia), are little affected.

Alkaline copper quat (ACQ) is an established wood preservative that is formulated with solubilized copper in amine solvent. This article describes three separate trials in Australia that investigated whether substituting soluble copper with micronized copper affects performance. ACQ and micronized copper quat (MCQ) performed similarly in Pinus radiata against four brown-rot fungi in a soil-block bioassay, while MCQ performed slightly better against two white-rot fungi in Eucalyptus delegatensis. A 2.3-year in-ground stake trial in the wet tropics at Innisfail also found that ACQ and MCQ performed comparably in P. radiata and Corymbia maculata. This was a severe test site with attack caused by soft-rot fungi, white-rot fungi, and termites. An H3 (outside, aboveground) field test against termites in Darwin showed that ACQ- or MCQ-treated P. radiata and C. maculata performed similarly against Coptotermes acinaciformis and Mastotermes darwiniensis. These trials demonstrated that MCQ performs comparably to ACQ under the test conditions used.

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The latest revision of Australian Standard 5604 on natural durability includes marine borer resistance ratings for many of its listed timbers. This paper describes the trials and reasoning behind the development of the marine borer resistance classes. Fundamental to this work was a small specimen test of 25 untreated hardwood timbers exposed at three marine sites: Port Stephens in NSW The Victorian sites of Williamstown and Geelong Williamstown had greater marine borer hazard than Geelong, perhaps due to its calmer waters. The most durable species in the trial were turpentine (Syncarpia glomulifera), iroko (Chlorophora excelsa), grey gum (Eucalyptus propinqua), brush box (Lophostemon confertus), red ironbark (E. sideroxylon), New England blackbutt (E. andrewsii), white mahogany (E. acmenoides) and river red gum (E. camaldulensis). Pinus radiata treated to 2.4% m/m CCA was the best performing timber. Information for additional timbers was obtained from an earlier aquaria trial, and trials conducted in Sydney Harbour some 40 years to 70 years ago. Comparison with known service lives for untreated marine piles in Victoria allowed the natural durability classes also to predict possible service lives for timbers previously not used as marine piles in the southern waters of Australia.