Heartwood specimens ofsugi (Japanese cedar, Cryptomeria japonica D.Don) were coated with solvent-born penetrating or water-born film-forming wood preservative semitransparent coatings, then examined in comparison to untreated specimens under the followingconditions: Standardcondition (S) based on JIS K 5600-7-7：2008 (filtered xenon-arc radiation, method 1, cycle A, 38°C, and irradiance 60 W/m²), conditions in which the water spray time was doubled or tripled compared to the standardcondition (W2, W3), conditions in which the temperature was increased by 10°C or 20°C (T48, T58), conditions in which the irradiance was multiplied by 1.75 or 2.5 (I1.75, I2.5), the condition with three times longer water spraytime；48°C；and 1.75 times igherirradiance (C1), thecondition with three times longer water spray time；48°C；and 2.5 times higher irradiance (C2), and the condition with the same set temperature and irradiance as the standard condition without water spraytime (W0). Infrared spectroscopy was used to evaluate the chemical changes on the surface of the specimens during the testing. The results indicated that the chemical changes on the surface of the specimens did not depart significantly from the changes observed in the outdoor weathering test under any of the conditions. Additionally, the pattern of change in color difference, water repellency, and gloss in each condition was confirmed to be similar to that observed during the outdoor weathering test.

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Two types of fireretardants (Ammonium phosphate-Boric acid and Guanidine phosphate types) and their treated wood were tested to clarify the conditions for the occurrence of deliquescence of fire retardant wood based on the relationship between the water vapor pressure (WVP) of the fire retardant in wood and WVP in the air. As a result, it was found that in WVP test of the fire retardants using the saturated salt solution method, the Ammonium phosphate-Boric acid type chemical had a high possibility of causing deliquescence at a relative humidity (RH) of more than 70 %, while the Guanidine phosphate type had a high possibility of causing deliquescence at a RH of more than 90 %. In addition, when the fire retardant woods were kept at a constant temperature and the RH was gradually increased from 60 % to 95 %, it was confirmed that the Ammonium phosphate-Boric acid type chemical deliquesced at 70% RH and the Guanidine phosphate type chemical deliquesced at 95 % RH. Furthermore, considering the effect of absolutehumidity (AH), which indicates the amount of water vapor in the air, each fire retardant woods was exposed to gradually increasing temperatures from 28℃ to 44℃ at a constant RH (60 %), but no increase in the weight of the fire retardant wood due to moisture absorption, and no occurrence of deliquescence. These results indicated that RH and WVP, but not AH and WVC, have a significant effect on the occurrence of deliquescence of these two types of fire retardant woods.

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