Kast~O~LITE© is a castable refractory cement manufactured by A.P. Green / Harbison-Walker. It is used as the insulation material in foundry furnaces and forges. Its maximum temperature is 2600 Degree Fahrenheit . You'll need 86 lbs of material per cubic foot, not counting mixing losses.
Refractory cement is unlike regular cement in that regular cement has water bound up in the compound. Heating regular cement will cause the water to flash to steam and destroy the structure. Refractory cement allows the water to be driven off during curing and in the initial heating. Refractory cement has elements that trap many microscopic air pockets in the mix that provide a high degree of insulation.
Castable refractory cement can be cast in sheet metal forms to create a furnace body. It is worked just like a light weight concrete or masonry mortar. The manufactures literature specifies that 86 pounds of cement will fill a cubic foot of space. Thus a 55 pound bag will cast approximately 1,105 cubic inches. Be sure to get extra cement to allow for losses in mixing and pouring. It's a problem to get into a job and find that you don't have enough. Make up brick shaped forms to use any extra. These bricks make great surfaces for welding or brazing.
Refractory material has various materials in it to create tiny air pockets after curing. These air pockets are what actually insulates the furnace. Typically the manufacturer creates these pockets by adding vermiculite to the mix. This is can cause the curing to be deceptive, because the vermiculite can trap and hold water, even though the cement has kicked off and cured.
The refractory should be allowed to cure for approximately 24 hours before firing. This is an important time, and the longer you can wait, the better. As with concrete, keep the surface from drying out by covering with wetted cloth or burlap if the weather is hot or dry. Also keep in mind that this material does not set as hard and strong as concrete, due to all the trapped air pockets, different cement, and lack of aggregate.
The initial firing, known as calcining, is critical. During this time the refractory is slowly heated from room temperature to the full operating temperature. This should be done over a long time as well, to allow the steam to escape the refractory. Here's a copy of the Manufacturer's Mixing and Curing Instructions.
After the initial firing the unit is ready for use, or ready to have a secondary coating such as ITC-100 or ceramic fiber blankets applied.
WARNING: Do NOT apply any surface coatings, such as ITC-100 or ceramic fiber blankets until the refractory is fully cured and fired. Sealing the surface has caused steam explosions as the refractory heats!!
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Revised: 2-21-08