Fire performance of thin intumescent coatings: Material characterisation and application to mass timber structures

This study investigates the thermal behaviour of two opaque and one transparent thin intumescent coating at material level (coating only) and system level (coating applied at real scale on timber), and their effects on timber in fire. Micro-scale tests were conducted to examine the underlying mechanisms of intumescence and degradation for each coating individually, while bench-scale tests demonstrated how these behaviours translate to larger scales. Critical temperature and heat flux thresholds were identified at which the coatings begin to insulate the timber through the formation of the intumescent char layer, as well as those marking degradation of the layer and the reduction of its insulating efficacy. The findings highlight that coating type and thickness, heating conditions and exposure duration influence mass retention, swelling pattern, and the integrity of the intumescent char layer. Overall, the transparent coating exhibited lower durability than the opaque ones. It was also shown that, due to the similar temperature ranges of timber pyrolysis and coating swelling, timber degradation occurs close to the coated surface during the transient swelling process, resulting in a heated region of 15-20 mm with negligible mechanical properties by the end of swelling. Therefore, intumescent coatings provide insulation progressively rather than immediately. • Integrity of swelled coating is influenced by type, thickness, and heat exposure • Transparent coating swelled layer exhibited lower durability than opaque coatings • Coatings on timber substrate swell faster and at lower heat fluxes than on steel • Timber 15-20 mm from the coated surface has minimal strength by the end of swelling