A pre-mixed, fiber-reinforced, high-temperature silicate mortar for setting, coating or repairing firebrick. Used extensively as the mortar between firebricks when building fireplace fireboxes. The ideal high-heat sealant for masonry-to-masonry joints is less than 1/4 Inch thick. Effective in resetting and cementing furnaces, stoves, chimney collars, boilers and duct work. Not intended for exterior use.