Refractory cement is a mixture of materials designed to withstand temperatures in ovens, fireplaces, kilns and furnaces. The castable variety can be molded by hand or poured into forms to create whatever shape is desired. You can use castable refractory cement to make replacement firebricks for a custom fireplace or a pizza oven. Because the material uses water as part of the curing process, any molds you use, such as sheet metal or tightly constructed wood forms, must hold in moisture.
Spray the form liberally with cooking oil.
Stir the entire container of dry refractory cement first, to ensure complete distribution of ingredients.
Measure out the proper amount of dry mix and dump it into a plastic bucket. Consult the package directions to determine the required amount of water. Add the water to the bucket and stir well with a stick.
Form a handful of the material into a ball. Hold the ball in the palm of your hand. If it flattens out, the mix is too wet and more dry mix must be added. Throw the ball from one hand to the other four or five times. If it falls apart, the mix is too dry and more water must be added.
Pour the properly prepared mix into the mold. Use your hands to pat it into the mold and smooth the surface. Don't use a trowel to smooth the cement. A slick finish interferes with the curing process. Leave the mold to dry thoroughly for at least 24 hours, preferably more. Consult the package directions for recommended cure time.
Remove the item from the mold carefully once properly cured. It will be delicate until it is fired.