MOKUZAI HOZON (Wood Protection)

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Over the past few decades, the methods used in the construction of foundations in Japan’s wooden houses have developed. Recently, even conventional foundations have been constructed using concrete to cover the soil, thereby making it moisture-proof. In addition, the use of another type of insulated and airtight foundation has increased, particularly in cold regions. However, insulated, airtight foundations have none of the openings for ventilation that are generally observed in conventional foundations. For this research, we conducted two surveys to examine the effects of humidity on wood in the crawl space of wooden houses under real living conditions. In one survey, the humidity levels in four houses with different foundations were monitored for one year. In the other survey, the humidity and moisture content in a house with insulated, airtight foundations were monitored for 17 years. Our findings showed that the crawl space environment in houses with insulated, airtight foundations had a low humidity of 40%-80% throughout the year. This finding suggests that insulated, airtight foundations posed no risk of causing high moisture content in the wood. In contrast, houses with conventional foundations with ventilation openings exhibited over 80% humidity in the summer. This finding suggests that conventional foundations may lead to the high moisture content in the wood. Furthermore, the humidity risk was higher in the house with moisture-proof-covered soil foundations than that in the house with uncovered soil foundations. This difference in humidity levels was due to the low temperature prevalent in the crawl space.

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When working with wood, coatings suited to the intended end-use application are employed. In wood with a porous structure, the paints penetrate the wood, influencing the weatherability and colourability of the wood. Roughly sawn texturing and laser micro incising were studied as methods to increase paints penetration into wood. This study investigated linseed oil penetration when applied to sugi wood subjected to plasma treatment, which is a widely used technique in microfabrication and surface modification. The results showed that the weight percentage of linseed oil that penetrated wood specimens was comparatively higher for samples that had been plasma treated for 30 minutes or 120 minutes compared to the untreated wood samples. For all of the treatment conditions, linseed oil penetration depth was deeper for latewood than earlywood, and linseed oil penetrated deeper into plasma-treated wood than into untreated samples.

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