Abstract: In order to study the fire resistance effect of thin rendering layer on insulation material, cone calorimeter tests were conducted with a 50 kW/m2 radiant heat flux to simulate the thermal exposure of a large-scale window fire. The fire resistance effects of rendering layers were studied by comparing the combustion properties of polyurethane foam (PU), extruded polystyrene foam (XPS) and graphite extruded polystyrene foam (GXPS) and the fire resistance properties after applying the thin rendering layers with thicknesses of 3, 5 mm and 7 mm respectively. The results show that there are obvious differences in the combustion properties of the three insulation materials without rendering layer. The ignition and peak heat release rate (PHRR) times for PU are the shortest, and its PHRR is the lowest. With a rendering layer, though it does not prevent ignition, the fire resistance properties of each insulation material are significantly improved: the ignition time is prolonged, the PHRR, the peak smoke release rate (PSPR) and the total smoke production (TSP) are reduced, the fire performance index (FPI) is increased, and the fire growth index (FGI) is decreased, and the fire resistance effect is further enhanced with the increase of rendering layer thickness. The fire resistance mechanism is mainly due to the rendering layer reducing the temperature rise rate of the insulation layer, slowing the escape rate of the pyrolysis gas, and blocking the contact between materials and oxygen, thus reducing the fire risk.

Key words: polyurethane foam, extruded polystyrene foam, graphite extruded polystyrene foam, thin rendering layer, combustion performance, fire resistance effect