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Abstract
The extent of boron penetration in framing lumber treated by spray applications during construction is not well quantified. This study evaluated the effect of formulation and concentration on diffusion of boron in lumber specimens that were equilibrated in conditions that produced wood moisture contents of 18 to 21 percent. One set of specimens was pressure treated with water before equilibration. Borate solutions were prepared from powdered disodium octaborate tetrahydrate (DOT) or from two commercial glycol-borate formulations and applied with a garden-type sprayer. The DOT solution was applied at a 15 percent concentration, while the glycol-borate formulations were applied at 15 and 23 percent concentrations. Boron penetration was evaluated after 6, 13, and 26 weeks and boron retention after 26 weeks of diffusion. Boron penetration was observed for all treatments and progressed for the duration of the study. There was no significant penetration difference between the powdered DOT and glycol-borate solutions when they were applied at the same (15%) DOT concentration. However, after 6 weeks, the glycol-borate solutions applied at the 23 percent DOT concentration produced significantly greater depth of penetration than the solutions applied at the 15 percent concentration. The exception was the 15 percent DOT solution applied to the specimens that had been wetted and then dried down to equilibrium conditions. These specimens had the greatest penetration, possibly as a result of their higher equilibrium moisture content. Retention analysis revealed that the glycol-borate solutions applied at the 23 percent DOT concentration yielded significantly greater boron retentions in the outer assay zone. This effect was less apparent for the inner assay zones. Although boron retentions in the outer assay zone were below those standardized for pressure-treated wood, in some cases they exceeded reported concentrations needed for protection against termites and decay fungi.
^Borate preservatives are used in a wide range of applications to provide protection against fungal and insect attack. One such application is the treatment of framing lumber used in interior construction. Pressure treatment of framing lumber with borates has become accepted practice, and research has demonstrated that these treatments result in deep penetration of boron into the wood (Morrell and Lebow 1991; Morris et al. 1996, 1997; Baker et al. 2001; Lebow et al. 2005). Borate formulations may also be spray...