Abstract
Wood decks are used in outdoor condition and their durability, such as decay resistance, is most important property for safety use. To prevent biodegradation, wood should be maintained at low moisture condition, but surface checks occurring in long time use may make inside moisture content high. In this study, surface check observation and visual decay grading of sugi（Cryptomeria japonica ）, hinoki（Chamaecyparis obtusa ）and redwood （Sequia sempervirens ）decks exposed outdoor for 10 years. Water absorption and drying test of redwood with sawn slit（0.5, 1, 2cm depth）were also carried out. Number of checks were large in hinoki decks and checks depth of 2cm were observed in sugi and hinoki decks, in contrast with 1 cm depth in redwood decks. Sugi and hinoki decks were also marked higher rot level. As a result of water absorption test, deeper slit on flat grain caused higher inside moisture content. Only in the case of 2cm depth slitted specimens, moisture content at slit bottom was kept enough high for wood decay after 48 hours drying. Results of observation and water absorption and drying test indicate that over 2cm depth check on wood surface may increase risk of decay significantly.
