Developments in Borate Treatment of Canadian Species for Decay and Termite Resistance

IRG/WP 07-30443

Jieying Wang, P Morris, S McFarling, T Byrne

The increased interest in boron treatment of wood over the past 20 years is mainly due to its environmental acceptability, potentially deep penetration in wood, and its efficacy against decay and termites. Based on Forintek’s research in the past two decades, the boron penetration and retention requirements for decay and termite protection in various national and international standards for Canadian wood species can be achieved using a combination of pressure treatment schedules and a short diffusion period. These standards may also be met by a new non-pressure process, demonstrated by Forintek with mountain pine beetle-affected lodgepole pine. If only decay protection is required, adequate penetration with lower loadings of borate may be achieved using conventional dip-diffusion treatment. In collaborative research between Forintek, the University of Hawaii and the University of Kyoto, the ten years’ results have confirmed that borate treatment provides long-term protection against decay and subterranean termites, including Coptotermes formosanus Shiraki in protected above-ground field tests simulating sill plate use. Since the biggest disadvantage of boron-treated wood is the chemical loss when in contact with liquid water, research has been carried out on boron fixation, but the most practical and successful method could be application of specific coatings on borate-treated wood. This has been in practice for exterior uses in New Zealand and the UK for decades. Results from a 10-year painted L-joint test by Forintek demonstrated the long-term decay resistance of borate-diffusion-treated hem-fir with a low retention of 0.2 % boric acid equivalent under exterior above-ground applications with surface protection provided by a three-coat paint. Forintek’s recent accelerated testing has also shown that retardation of boron leaching can be achieved using certain water-based transparent coatings. The colourless nature of borates plus the transparent coatings allows improved durability while maintaining the natural appearance of wood. Long-term field tests for engineered wood products treated with borates and surface protected with a water-based transparent coating are now underway.

Keywords: boron, borate, disodium octaborate tetrahydrate (DOT), diffusion, pressure treatment, termite resistance, decay resistance.

Conference: 07-10-29/11-02 Taipei, Taiwan

Download document (153 kb)
free for the members of IRG.

Order document from secretariat