Fire performance of multi-layer fire-retardant systems for exterior wood products

Intumescent paints could be used in exterior applications and provide beneficial fire protection for structures located in wildfire-prone areas if the paints were more durable to weathering. A limited number of studies have evaluated the effectiveness of intumescent paints on wood post-weathering, and they have shown that the service life is relatively short, on the order of about one year. None of the previous studies assessed the effects of applying multiple coatings, including an acrylic latex color, bonding primer, and acrylic topcoat, over an intumescent paint. The effects of proper versus improper coating application have also not been evaluated. Here we used a cone calorimeter at three heat fluxes to investigate the fire performance of multiple combinations of coatings applied to cedar shingles. Depending on coating combination, specimens were subjected to either natural or accelerated weathering. The results showed after one year of natural weathering that no char expansion of the intumescent paint occurred, indicating all coating systems failed with UV and moisture degrading the topcoat(s). With similar thickness, application method had little effect on overall fire performance of the coating systems both before and after accelerated weathering.