Non-water soluable. Used for joining or repairing masonry flue tile or as a parge coating for building fireboxes. Hydraulic set mortar that does not require heat to cure. Resists washing out when exposed to rain or water. Develops a compressive strength a bove 2500 psi and withstands 2550-degrees fahrenheit without softening. Meets or exceeds all the requirements of the National Fire Protection Association standard NFPA211, 1988 edition. Covers 1268 sq. in. 1/8" thick, enough for approximately 50 clay flue tiles, 8" x 8", or 30 firebrick, 4-1/2" x 9".