This is our original fireplace mortar formulated especially to patch fireplace fireboxes and to bond firebrick to firebrick. Fireplace mortar is a silicate product that when fire cured, sets rock hard - as strong as firebrick itself and withstands 2000° Fahrenheit. Comes in a convenient cartridge for easy repointing of fireplace brick within the firebox. Colors match most mortars. Passes ASTM E136 and E72. 10.3 oz. cartridges.