The effects of sanding process prior to re-finishing on the performance of wood preservative semitransparent coatings were examined. Sugi heartwood specimens that had been once finished with several coatings (6 water-borne and 2 solvent-borne) and weathered for 24 months at 45 degrees facing south in Tsukuba were subjected to sanding to remove old finish. They were then re-finished with the same coatings as before, and weathered again for an additional 24 months. For all the coatings, the mean coating weight (wet, g/m²) of re-finishing was larger than that of initial finishing, regardless of whether the specimen was sanded or not prior to re-fishing. The color of the re-finished surfaces was characterized by decreases in both lightness (L ^*) and chromatic values (a ^*, b ^*) compared with those of initial finishing. This tendency, however, became weak for the specimens re-finished after sanding. The weatherability of the specimens after re-finishing was better compared with initial finishing, in terms of color stability and water repellency. This may be due to the increased coating weight of re-finishing. In particular, the specimens re-finished after sanding showed much higher water repellency and the fewest surface defects. This indicates that removing old finish by sanding may provide a better surface preparation for re-finishing.

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Laboratory evaluation of wood preservatives was performed to determine their resistance to the drywood termite, Incisitermes minor (Hagen). Wood preservatives listed in JIS K 1570 (2004) were impregnated to sugi sapwood samples (20mm(T) × 20mm(R) × 10mm(L)) to K3 and K4 levels in Japanese Agricultural Standard (JAS). The treated samples were subjected to the weathering procedure described in JIS K 1571 for impregnation treatment. Non-fixative waterborne disodium octaborate tetrahydrate (DOT) was impregnated to the same size of sugi sapwood to two levels of the retention at 3kg/m³ boric acid equivalent (BAE) and 6kg/m³ BAE, followed by drying procedure described in JIS K 1571 for impregnation treatment with non-fixative wood preservatives (JIS K 1571 Appendix Normative). Each treated sample was forced to feed on twenty psudergates of I. minor under 26°C, 75% R. H. for 6 weeks.
The average mass loss of untreated sugi sapwood reached over 15%, and those of treated specimens with wood preservatives listed in JIS K 1570 were under 3% even after weathering, satisfying the threshold of JIS K 1571. The average mass loss of treated specimens with DOT at 6kg/m³ BAE was 2%, satisfying the threshold of JIS K 1571.
Timbers used in interior and dry conditions are recommended to be treated at K1 level in JAS with boron compound at over 1.2kg/m³ BAE for protecting from biodeterioration by wood-boring beetles and dyrwood termites. Our results suggest that higher retention level of wood preservatives in timbers is necessary for resistance to the drywood termite, I. minor.

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