Influence of moisture absorption on the degradation of fire-retardant-treated and surface-coated wood: Effect of water spray duration under accelerated weathering

To explore the influence of moisture absorption on the degradation of fire retardant (FR) treated wood, two accelerated weathering conditions that differ in water-spray durations up to 500hrs were tested. Sugi (Cryptomeria japonica) sapwood specimens were impregnated with the guanidine phosphate-based chemicals as a fire retardant, then coated with or without one of the four types of coating materials (penetrating, semi-film-forming, and two kinds of film-forming). The specimens were exposed to artificial accelerated weathering to be compared with outdoor weathering previously reported. In addition, moisture content during water spraying was monitored for 168hrs using another group of specimens without any FR treatment. Results showed that the rates of leached chemicals are proportional to moisture content absorbed during water spray. Thus, adjusting the water spraying duration possibly optimizes accelerated weathering to equally accelerate the leaching of FR chemicals, regardless of the types of coating materials. Comparison with outdoor weathering implied that 18min of water spraying in accelerated weathering is too short and 72hrs of water spraying is a little long for specimens 18mm thick.