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 2 000° fahrenheit, Comes in a convenient cartridge for easy repointing of fireplace brick within the firebox, Size: 10, 3 oz, cartridge, Joins and repairs masonry, firebrick, Tuckpoints fireplace, fireboxes and firebrick, It is not for metal applications, Water soluble until firecured, Silicate mortar, Meets ASTM E136, Requires heat to cure, Internal only, Buff color, SKU: RTLD121