Comparative study on the fire behaviour of fire-rated gypsum plasterboards vs. thin intumescent coatings used in mass timber structures

The experimental study presented herein describes a comparative investigation on the fire performance of fire-rated gypsum plasterboards and thin intumescent coatings used in mass timber structures. Timber samples, (1) unprotected, (2) encapsulated with fire-rated gypsum plasterboard(s), or (3) coated with a thin intumescent coating, were fire tested using the H-TRIS (Heat-Transfer Rate Inducing System) test method. Samples were tested until the heated surface of protected timber had reach a 300°C threshold (or for at least 1 hour of heating) under a constant incident radiant heat flux of 50 or 100 kW/m2 . As expected, unprotected samples quickly ignited, while samples with plasterboards or thin intumescent coating showed a delay on the onset of timber charring and a reduction of the average charring rate after initiation of charring. The intumescent coating demonstrated a high dependency on the heating conditions. This experimental study offers an interesting comparison between the fire behaviour of timber protected with plasterboard vs. protected with intumescent coating. At the start of the heating exposure, the coating rapidly swelled up to a quasi-steady thickness. The number of plasterboards and Dry Film Thicknesses (DFT) of the intumescent coating was varied for enabling a comparative analysis between the fire behaviour of the two protective methods.