In the mid 1990s, FPInnovations - Forintek Division (then known as Forintek Canada Corp.) initiated a study of borate-treated lumber above ground, protected from rain but exposed to termites in Kincardine, Ontario and, in collaboration with other researchers, in Japan and Hawaii. The material included hemlock and amabilis fir lumber treated with borate and chromated copper arsenate (CCA). Reference materials included Hinoki in Japan, ACZA treated Douglas-fir in Hawaii and western red cedar in Canada. The samples were evaluated annually for termite attack. Generally in Canada all of the treated material was found to be performing equally well, with some pieces showing residual signs of earlier superficial feeding or cosmetic damage. Attack was moderate on untreated controls. This was also the case in Japan with the exception of 2% borate shell treatments with DDAC in which two samples were rated as moderately or severely attacked. In Hawaii, where termite attack was more severe, CCA and 3% borate through treatments performed better than the others.
After ten years of exposure, the tests in Japan and Hawaii were terminated and the test samples were returned to Forintek. The Hawaii samples, which had suffered more termite damage than those from Japan, were examined by Forintek’s CT scanner to determine the extent of internal damage not detectable by a visual rating of the pieces. This revealed that the 3% through borate treatments contained the least termite damage though 2% through borate treatments had negligible attack. The borate treated pieces returned from Hawaii were also subjected to measurements of compression stiffness at seven points along their length. Results showed that the stiffness of any specimen was similar along its length. Only the 2% shell treated samples showed statistically significantly lower stiffness than the 3% through treated samples which had no internal damage.
Five borate-treated dodai from each group returned from Hawaii and Japan were destructively sectioned for analysis of residual borate. Patterns of borate distribution were plotted. Generally, the amount of borate retained was less on the outer surfaces (top, sides, and bottom). There did not appear to be a correlation between the treatment type (i.e. shell or through, 2% or 3%) and the percentage of borate retained, nor between the rating given the piece for decay and the percent of borate retained.
In summary, ten-year results of field exposure in Hawaii and Japan, in relatively aggressive termite feeding situations, support the conclusion that borate treatments, as well as CCA and ACZA treatments, can provide long-term protection from destructive termite attack to structural lumber. A 3% BAE through-treatment performed comparably to CCA treated hem-fir in Japan and Hawaii. Plantation-grown Hinoki showed termite attack at the same rate as untreated hemlock.