Rutland\'s original fireplace mortar formulated especially to patch fireplace fireboxes. For bonding firebrick to firebrick. Fireplace mortar is a silicate product that when fire cured, sets rock hard, as strong as firebrick itself. Comes in a convenient cartridge for easy repointing of fireplace brick. Apply with standard caulking gun. Colors match more mortars. Withstand 2000<deg> F. Not for exterior use. Passes ASTM E136 and E72. 10.3 oz. cartridge.