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, Not for exterior use, Colors match most mortars, 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, 2000 deg F max, Internal only, Color: Gray, SKU: RTLD122