Cement Furnace 8Oz Black Non-asbestos. Spreads easily, bonds and seals metal-to-metal and metal to masonry joints under 1/8?. Durable as firebrick when heat cured. Resists temperatures up to 1093 Deg. C (2000 Deg. F). Use when installing or resetting furnaces or oil burners. Prev ents air and gas leaks in flue and chimney joints. Can be used on cast iron, steel or firebrick.