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Dan Fronefield

Making insulating castable refractory from common materials

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While I trying to develop a cheap, easy and lightweight castable insulation for forges or casting furnaces, I came across the answer !!! Someone ... probably lots of someones beat me to it.


Although I have not tried this formulation, it should work fine as a castable high temp insulation (good to 3000 degF). I'd coat the inside of any forge/furnace with Satanite, ITC-100 or similar product as a refractory coating.


See Website for full instructions: HTTP://WWW.JOHN-WASSER.COM/NEMES/MAKEICR.HTML


Material you will need:

1) High Temperature Furnace Cement (hardware store) - Suggested: Worcester Brush HIGH TEMP Furnace Cement (Black) - $5 per quart

2) Perlite (garden store) - $5 per 2 gallon container

3) A little water

4) A rubber spatula



1 part by volume Furnace Cement

4 parts by volume Perlite

2 cups water per gallon of cement

Mix to thin plaster consistency



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I came across variants of this recipe about a year ago when I first started playing around with making a casting furnace. The guys at Backyardmetalcasting.com have played with a number of similar recipes as well. They work pretty well at aluminum melting temperatures, but the mica (Perlite) will melt at about 2000 F. That's most of the substance of your lining (using the ratios you've given), so it'll tend to break down fairly quickly after that. I wouldn't recommend using a high-Perlite mix in a forge that I planned to do a lot of welding in. Even in a forge that's not intended for welding, don't expect it to be as durable as straight commercial castable.


I just used commercial castable (Mizzou from Darren Ellis) for the first time in the forge I'm working on right now. Personally, I'm sold. It's so much easier to work with than the homemade stuff, and you know what you're getting. I doubt I'll ever go back to the homemade stuff.

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