Castable Refractory—A refractory mixture with heat resistant hydraulic cement and binders that can be cast in place. Castable refractory has many applications in industry as well as in ceramics studio. It is often used in kiln construction because it is easy to use and mix, and reasonably priced.
Advantages
Castable refractory has many benefits over traditional bricks because it can be mixed on site and poured into molds of almost any shape. The forms are also relatively easy to construct. This leaves fewer joints that can leak heat or air. And, unlike hard-brick construction, you don’t need a chisel and hammer or a wet saw to make hundreds of cuts.
This material is often used by potters in kiln building to cast the kiln floor (both car and standard kilns). This is easy because you just make a square or rectangular form, seal it with something like Vaseline, and pour in the castable, giving you a level and smooth floor for your kiln. It is also commonly used to form the key block in standard sprung arch and anagama kilns. This eliminates the need to make complicated and precise cuts, which saves time and reduces mistakes. The key block is cast in place by sealing the top of the arch form and pouring in the castable. The walls and gravity hold everything in place while it cures. Some people cast the entire kiln, including the door (made of cast brick shapes). Others only cast portions of the kiln—for example, building a kiln body with standard bricks and then casting just the sprung arch to save the expense of buying specialized arch bricks.
Castable refractory is also simply mixed in a wheel barrow with a mason’s hoe. It can be bought commercially or homemade. All you have to do is add water. Getting the water ratio right is the most difficult part; too much water may cause it to shrink and crack. The manufacturer’s instructions are precise and easy to follow and have specific directions for curing and firing. The castable must be fired very slowly so that it doesn’t blow up.
High-alumina castable can be used to make the trough in the bottom of a salt kiln fire box. This helps contain the salt that is poured into the kiln and preserves the floor from its destructive effects. This trough can then be periodically removed and replaced to extend the kiln’s life.
Knowing the properties of the materials allows us to exploit their positive characteristics. For example, hard-dense castable is strong and durable but uses a lot of BTU’s to heat up, while ceramic fiber is very fragile but is inexpensive and is a great insulator.
Firing the Castable
The first firing is a very important aspect of castable refractory construction. All potters are aware of the hazards of greenware blowing up in a kiln if it is fired too fast or too wet in the early stages. Now imagine that the pot is five inches thick and weighs 2 tons. If that blows up, it could easily destroy your studio and cause great injury.
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Article Source : https://ceramicartsnetwork.org/ceramic-recipes/recipe