Performance of borate-treated lumber in a protected, above-ground field test in Japan
K Tsunoda, A Byrne, P I Morris, J K Grace
This document is supplemental to the previous IRG document (Tsunoda et al. 2004).
An experiment to simulate the sill plate (dodai) of the Japanese houses was conducted at the termite field test site of the Research Institute for Sustainable Humanosphere of Kyoto University in Kagoshima Pref., Japan where two economically important subterranean termite species [Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe)] are established. DOT(disodium octaborate tetrahydrate)-treated hem-fir samples [Tsuga heterophylla (Raf.) Sarg. and Abies amabilis (Dougl.) Forbes]- 105 x 105 x 500 mm in size were placed on concrete blocks 19 cm above the ground surface. The test samples were prepared from sound wood samples pressure treated to supply 10 replicates of shell-treated materials at target levels of 2% BAE and 3% BAE. The subsequent diffusion storage produced another set of through-treated samples at the same target levels. Feeder stakes within the block hollows extended into the soil to facilitate the access of the termites to the wood samples. The assembled sets were covered with plastic boxes to protect the samples from the weather. Samples were annually inspected for termite attack and decay and visually rated according to AWPA standard since installation on December 21, 1995.
All treated samples still remained free from decay after 10 years’ exposure. In contrast, slight progress in termite attack was observed on a few treated samples within the last two years. Four samples with target retention of CCA 4 kg/m3 were slightly attacked with mean rating of 9.6 against termite attack after 10 years. This meant that the extent of termite attack did not develop after the first attack. Through treatment at 3% BAE performed as well as CCA 4 kg/m3 after 10 years with mean rating of 9.5. Although mean ratings of termite attack on the treated samples ranged from 8.8 to 9.6, statistical analysis showed no significant differences among all treatments.
Untreated hem-fir and hinoki (Chamaecyparis obtusa Endl.) controls showed progressive termite attack starting in the first year and were heavily attacked after 10 years’ exposure. Decay was found on 9 and 6 untreated hem-fir and hinoki, respectively.
Keywords: borate-treatment, disodium octaborate tetrahydrate (DOT), subterranean termites, sill plate (dodai), above-ground use, field test