Thermal Aging Effect on Various Characteristics of Alder and Spruce Coated with Fire-Retardant Paints

Aim of study: This study aimed to determine the effect of thermal aging at 70 and 150 °C for 624 h on the color, surface roughness, fire performance, and weight loss of alder and spruce wood coated with commercial fire-retardant paint containing antimony trioxide (Sb2O3) or titanium dioxide (TiO2).Material and method: Alder (Alnus glutinosa subsp. barbata) and spruce (Picea orientalis) specimens were coated with fire-retardant paint containing 1% and 2% Sb2O3 or TiO2 and thermally aged at 70 and 150 °C for 624 h. The color change, surface roughness (Rz), limiting oxygen index (LOI), and weight loss of the specimens were determined using the CIE Lab* system, ISO 4287, and ASTM D2863, respectively.Main results: Aging at 150 °C caused greater total color change than at 70 °C, while painted samples showed less noticeable color change than uncoated controls. Spruce showed greater fire-performance stability than alder. The highest LOI retention was obtained with 2% TiO2 at 70 °C and 2% Sb2O3 at 150 °C. The weight loss of samples at 150 °C ranged from 7% to 11%.Research highlights: Thermal aging temperature strongly affected color stability and fire performance. Sb2O3 and TiO2 improved fire-performance retention, with the effect varying according to wood species and additive type.