MOKUZAI HOZON (Wood Protection)

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Performance of smoke-dried wood on fungal and termite resistance was studied. The smoke seasoning was carried out for 15 days, and the maximum temperature at 80-90°C was continued for 6 days. Small blocks of Japanese cedar (Cryptomeria japonica) wood were treated with a smoke-drying facility. Treated blocks of 20×20×10mm (longitudinal direction) were directly subjected to decay test. Those of 26×26×16mm were cut into 20×20×10mm after treatment, and then tested. The surface removal of 3mm in thickness in the later specimens was aimed to know the depth of smoke penetration into wood blocks. Half of the samples were leached in the cycle of water soaking for 8h and drying at 60°C for 16h for 10 days. Decay resistance according to JIS A 9201 was evaluated using a brown rot fungus, Fomitopsis palustris. Mass losses of untreated wood, smoke-dried wood, and smoke-dried wood followed by surface removal of 3mm in thickness were 53%, 16%, and 21 % respectively. After leaching for 10 days, their mass losses were 38%, 51%, and 46% respectively. Smoke-dried wood had a little decay resistance against the brown rot fungus, however its effectiveness disappeared completely during the leaching. Mass losses of untreated wood and smoke-dried wood by Coptotermes formosanus for 3 weeks were 24% and 5%, and their mortality were 6% and 53% respectively. Smoke-drying did not have any clear effect on preventing the growth of Aspergillus niger, Penicillium citrinum, Penicillum funiculosum, Aureobasidium pullulans or Chetomium globosum. Smokcdrying increased water repellency on the wood surface.

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