Performance of borate-treated lumber in a protected, above-ground field test in Japan

IRG/WP 04-30344

K Tsunoda, A Byrne, P I Morris, J K Grace

This document is supplemental to the previous IRG document (Tsunoda et al., 2002). An experiment to simulate the sill plate (dodai) of the Japanese houses was conducted at the termite field test site of the Wood Research Institute in Kagoshima, 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 400 mm in size were placed on concrete blocks 19 cm the above 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 standards since installation on December 21, 1995. All treated samples still remained free from decay after 8 years’ exposure, although slight progress in termite attack was observed on a few samples of 5 treatments within the last two years. Three samples with a target retention of CCA 4 kg/m3 were slightly attacked. On the other hand, 3% BAE through treatment performed best with mean rating of 9.8 against termite attack. After 8 years’ exposure, 2-4 samples from each group of borate treatments (2% BAE shell, 3% BAE shell, 2% BAE through and 3 % BAE through treatments) were slightly attacked by termites. Untreated hem-fir and hinoki (Chamaecyparis obtusa Endl.) controls showed progressive termite attack starting in the first year and were heavily attacked after 8 years’ exposure. Incipient decay was first found on 7 untreated hem-fir and sapwood portion of two untreated hinoki during the 5th year of exposure, whereas 9 and 4 sustained slight to heavy decay after 8 years’ exposure, respectively.

Keywords: Borate-treatment, disodium octaborate tetrahydrate, subterranean termites, sill plate (dodai), above-ground use, field test

Conference: 04-06-06/10 Ljubljana, Slovenia

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