ABSTRACT This study compares the charring behaviour of mass timber under varied heating conditions when protected by either different thin intumescent coating types or fire‐rated plasterboard layers. Bench‐scale fire experiments were conducted using the Heat‐Transfer Rate Inducing System (H‐TRIS). Testing included cross‐laminated timber (CLT) samples with two opaque coatings (A, B), one transparent coating (C), and one‐ or two‐layer plasterboard assemblies, with bare timber as a benchmark. The dry film thickness (DFT) of the opaque coatings was 2.35 ± 0.25 mm, while the transparent coating had a DFT of 0.37 ± 0.03 mm, and each plasterboard layer was 13 mm thick. During testing, samples were exposed to three constant radiant heat flux levels of 25, 50 or 75 kW/m 2 for 60 min. Bare timber and samples with transparent coating experienced the most severe charring, while opaque coatings and plasterboard layers provided better insulation. All protected timber samples, even those with the transparent coating, showed a delay in the onset of charring and a level of reduction in the effective charring rate compared to bare timber. This study demonstrated that both thin intumescent coatings and fire‐rated plasterboard layers can delay the onset of charring and induce a reduction in the charring rate of mass timber, although increased heating intensities caused deviations in performance. Overall, the coatings were found to be more susceptible to elevated heating conditions than plasterboard, whose insulation capacity was dependent on its moisture content. The opaque coatings provided an equivalent level of fire protection performance to one layer of plasterboard, but the highest level of protection was achieved by the two layers of plasterboard.
Spyridakis et al. (2026) studied this question.