This work was designed as a preliminary investigation into borate loss during the drying, and planing of wood. The objectives were to investigate borate losses from wood dried under different regimes and to investigate the effect of planing dried borate-treated wood on the retention or distribution of the preservative.
Green nominal 1 x 2 inch amabilis fir was cut into 1015 mm long samples. The samples were pressure treated with disodium octaborate tetrahydrate and allowed to diffuse for two weeks. The samples were then cut into four end-matched sub-samples with three of the sub-samples being subjected to either dehumidification-, kiln-, or air-drying. The dehumidification and kiln-drying were done in a sealed chamber with a condenser attached. Condensed water was collected to check for loss of air-borne boron during the drying. The fourth sample was used for analytical and penetration data.
Boron in borate-treated lumber was found to be air-borne at temperatures as low as 30°C with higher temperatures increasing the amount of borate found. However, the residual borate content after drying was not significantly reduced at 30°C or 50°C.
The relatively rapid oven-drying of small borate-treated samples at 50°C prior to analysis resulted in no significant loss of borate. However drying samples at 105°C reduced the borate retentions significantly. This indicates that it would be preferable to dry at 50°C to reduce losses of boron prior to analysis, thus giving more accurate results. In practice kiln-drying often occurs at temperatures between 50°C and 105°C. Further information is needed on borate losses between these temperatures.
Because surface layers after drying, contain higher levels of borate, planing borate-treated lumber will remove a disproportionate amount of boron from the treated lumber. This suggests that higher initial retention levels will be required to meet standards if the wood is to be processed after treating.
Borate-treated lumber stored under the temperature and relative humidity conditions that can prevail in, for example, the crawl space of a Japanese house, did not lose significant amounts of boron.