How-To: Homemade Castable Refractories

How-To: Homemade Castable Refractories
DIY refractory mixture made from Perlite and furnace cement, courtesy of Dan's Workshop. The cast lid is reinforced with a grid of steel wires to increase tensile strength.

Wikipedia quotes ASTM C71 on the definition of refractory: “non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F.” They are commonly used, for instance, to line kilns and other high-temperature furnaces.

Castable refractories can be mixed with water, formed, and solidified like cement, but the process of drying the solid before full-temperature use is critical. When working with castable refractory, be mindful of the hazard of heating trapped water too rapidly and causing a steam explosion. If using a commercial mixture, follow the manufacturer’s directions closely. If using a DIY formula, use a gradual “bake out” process in which the cast material is brought up to final operating temperature very gradually, in a series of slow, prolonged stages, with full cooling phases in between.

There are several recipes for “homemade” refractories floating around the web, but Lionel Oliver’s tutorial over on is one of my favorite resources on the subject.  Lionel has been experimenting with and writing about home foundry work online for more than a decade, now, and his recipe uses no hard-to-find materials. By volume, it is 3:3:4 Portland cement:perlite:silica sand, mixed together thoroughly, then combined with 4 parts fireclay. The dry ingredients are then moistened to the texture of “stiff cookie dough,” packed into a form, and allowed to dry thoroughly before bake-out.

If you can get your hands on ready-made furnace cement, preferably of the “black” 3000 °F variety used to make repairs on wood-burning stoves, a simpler recipe is provided by John A. Wasser:

You will need about 1 part (by volume) of Furnace Cement for each 4 parts (by volume) of Perlite so for a two gallon bag of Perlite you will need a half gallon of Furnace Cement. If you use much less than four volumes of Perlite for each volume of Furnace Cement all of the passages between Perlite beads will be sealed and it will take a long time for the cement to set (it needs contact with air). If you use much more than five volumes of Perlite for each volume of Furnace Cement the resulting material will be quite weak. You will also want to have some Furnace Cement to use as a sealing coat on your lining. The Furnace Cement has about the consistency of roofing tar and is very sticky. It is MUCH easier to work with if you add about 2 cups of water per gallon of cement. This makes it more like a thin plaster.

Here’s a page from Dan’s Workshop showing John’s refractory mixture in use in the construction of a small electric furnace.

5 thoughts on “How-To: Homemade Castable Refractories

  1. TJ says:

    I was unable to find fireclay in my own town. Instead I used Aluminum Oxide aka alumina. It’s working really well for me. You can find alumina from sand blasting companies. They tend to throw it away.

  2. Dynamo Dan says:

    Thank you makezine! – Dan

  3. John Wasser says:

    OMG! I’ve been mentioned in Make! :)

  4. sunergeo says:

    John’s site appears to be offline :(

  5. Shelly Gorden says:

    Nice tips about Homemade Castable Refractories. I got some important information about refractory castable from your informative blog. I also want to share some information about this topic.

    High alumina refractory cement is a hydraulic cementing material with mixing the power of calcium aluminates and clinker with Al2o3 50% up and down. It has other names of ‘high alumina cement’ and ‘aluminous cement’, the main composition of high alumina cement clinker are CA and CA2 with a little C12A7,C2AS and micro MA and CaO,TiO2, Fe2O3. There are different methods making high alumina cement from bauxite and limestone, such as by rotary kiln, electric arc furnace melting , reverberatory melting . The one by rotary kiln is more popular inChina as its lower energy consumption. Everyone can get more information from regarding North refractory castable.

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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