Section 7-2.10.2 of NFPA 211 states that clay flue liners must be imbedded in a "non-water soluble calcium aluminate refractory cement mixture..." Flue Goo II is such a mixture. It is specially designed, gray-colored refractory cement that is non-water soluble after drying. Use Flue Goo II for flue tile installations, as well as for setting firebrick and parging the walls of smoke chambers. Sold in powder form in resealable, 1 gallon plastic tubs. Each gallon will set about 10 - 20 flue tiles, 30 firebrick, or will cover 4 - 6 sq. ft. when parged to a thickness of 1/8" - 1/4". Not for exterior use.