Stir the dry contents of the container thoroughly. Using a plastic bucket or container, add one quart cool, clean water per 12.5 lbs. dry mix. Only mix an amount that can be used within 20-30 minutes after adding water as cement sets up fast. Mix thoroughly, taking care not to lose any water. While wearing gloves, take a handful of the material and form it into a ball. Toss the ball an inch into the air a dozen times. If it breaks apart, it is too dry. If it slumps or sags down through the fingers, it is too wet. Excess water lowers the strength of the bond and increases time needed to set.
Firebox: Dampen work area lightly with water. Put into place and pat it to remove air pockets. Do not smooth to a slick finish as this prevents water from escaping.
Casting: The form or mold must be waterproof to prevent absorption of water from the mixture, as water is needed for the hardening process. Apply release agent, such as cooking spray, to the form or mold. Pour mixture into the mold and smooth by patting thoroughly to remove air pockets, but do not smooth to a slick finish as this prevents water from escaping.
Setting and Firing: Let set at 60°F or above for 24 hours. Do not permit surface to dry out during this period. Dried castable cement still contains chemically combined water that is given off as steam at higher temperatures. Therefore, heat slowly when first starting fire.