Distribution of Boron Through Glue Lines in Laminated Wood

In this study, the distribution of borates and boron content in disodium octaborate tetrahydrate–treated Radiata pine specimens was investigated. Specimens conditioned to either 12% or 40% moisture content were treated with 15% either glycol- or water-based disodium octaborate tetrahydrate (Na₂B₈O₁₃·4H₂O) and then conditioned at high relative humidity (>90%) for varying durations for 1, 2, 3, and 4 weeks. The study also examined the impact of glue lines on borate distribution and content. Borate coverage (%) was measured in the radial direction in wood block specimens, while borate concentrations were determined across the entire radial plane of another set of specimens, which were sliced every 10 mm starting after the glue lines. The results showed that while boron concentrations in the first analysis zone (5–15 mm) were generally higher in non-laminated specimens than in laminated ones, boron still diffused through the glue lines into this zone. The propylene glycol–disodium octaborate tetrahydrate treatment proved more effective in specimens conditioned to 40% moisture content. However, in air-dried specimens, boron levels in propylene glycol–disodium octaborate tetrahydrate–treated specimens were significantly lower than in those treated with water-based disodium octaborate tetrahydrate in the first analysis zone. This study concludes that glue lines do not serve as an effective barrier to boron diffusion in glue-laminated timber.

Cite this article as: Nami Kartal, S., Yi, T., & Singh, T. (2026). Distribution of boron through glue lines in laminated wood. Forestist, 76, 2912, doi:10.5152/forestist.2026.252912.