Comparative Surface Roughness Evolution of 33 Japanese Hardwoods after Water and Fire-Retardant Treatments Using 3D Optical Profilometry

In this study, we assessed the surface roughness of 33 Japanese hardwood species by 3D optical profilometry (ISO 25178) and examined the influence of water and fire-retardant treatments. The surface roughness on cross, radial, and tangential sections was evaluated using the arithmetic mean height (Sa) parameter. Measurements were performed on untreated samples and repeated on the same spots after water treatment and NF300 fire-retardant treatment. Surface roughness varied widely across species and anatomical sections and tended to decrease with increasing wood density. The surface roughness increased with both treatments compared to the untreated wood. The maximum increase was on tangential surfaces after NF300 treatment, where the mean Sa value increased from 30.14 ± 17.05 μm to 42.05 ± 19.60 μm (39.5%). The statistical analysis showed a significant difference between the untreated and NF300-treated tangential surfaces (p = 0.011).