MOKUZAI HOZON (Wood Protection)

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In Japanese traditional wood constructions, such as temple, timber bridge, castle and old folk house, several types of copper based metal fittings which called e.g. Giboshi, Hanakakushi, Nemaki, Kugikakushi, were used as a cover to protect wood members from rain waters. In some cases, bio-deterioration of wood members with metal fittings seems to be suppressed at not only directly protected area but wide area beneath the fitting. It is suggested that copper was released from metal fitting to wood members and acted as a wood protective agent. To confirm the release of copper, the surface of wood members of Kyoto Sanjo-ohashi bridge, which have copper Giboshi or Kugikakushi, was analyzed with handheld fluorescent X-rays analyzer. Surface analysis was carried out at 14 points on the two Giboshi posts, 4 points on the handrail bar and one point on the copper preservative treated Sugi post which mounted near the Sanjo-ohashi. The element contents were calculated from the intensity of fluorescent X-rays obtained at each measuring point based on Fundamental Parameter method. As a result, copper was detected at all 14 measuring points of Giboshi posts, and calculated copper contents were exceeded 0.4％, which detected from the preserved post surface, at 12 measuring points. In this study, it is confirmed that copper is distributed widely in the wood members near the copper metal fittings and copper content is likely enough to affect the bio-deterioration of wood.

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