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I Forge Iron

Trying an insulating refractory material


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I've decided to give a go with some EP kaolin, aluminum oxide, zirconium silicate, sawdust, and millet seed. The blend was about this by calculations:

32 lbs EPK
13 lbs aluminum oxide
5 pounds zirconium silicate
~ 1 pound saw dust
~ 10 pounds millet

I ran short of Aluminum Oxide so I substituted zirconium silicate for the balance.

The sawdust & millet was intended to be about 20% by volume. This along with whatever air gets trapped in the mix will provide gaps that should create the insulation properties once the compound is dried & fired. Frankly I am now feeling like I should have gone to 50% on the sawdust & millet. I want to let these panels dry and fire them to see how they look compared the the walls of my kiln.

The dry mix before dry blending


The mix after water & some machine mixing with a 1/2 inch eletric drill and a mud mixing attachment

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Here's what it looked like after being pressed in the mold


It's drying now. The shrinkage has been about 3/16 in. in 24 hours. That was enough to get it out of the forms. Total shrinkage after firing is supposed to be 11% - 12%.

Oh, dry any flat clay item on something like Hardie board or drywall. These materials tend to pull water out of the bottom of the piece and continue to dissipate the water. If you don't use something like that, the top dries way faster than the bottom and it starts to cup.

Hopefully the sawdust will keep it from cracking. Once it's dry it goes in the kiln to be fired as close to cone 10 as I can get it. That will burn out the sawdust and the millet. If all works according to what I've been able to research, this will yield an insulating ceramic panel.

Actually, it will probably have to go into the kiln for a day or so at 180 - 200 degrees until the water stops coming off it. The last thing you want in clay as it approached 1000 degrees is water. I've had this happen before and lost the piece with the water in it and several pieces next to it.

I have no idea if this is going to work for me as it has for others before me. We shall see. Keep you posted.
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  • 2 weeks later...

Failure is mine! Arrrgh!

I did a test firing today on a small piece. It was hand built so it wasn't as dense as the panels that are still drying. As is past 500 degrees it was a cracked pile of black stuff. The clay had shrunk in past the seeds. Black, charred seeds were on the surface. The whole thing was black. I looked like a pile of ash.

At about 900 it turned white and I had some hope it might vitrify into something eventually. I increased the target to cone 7.

At about 1250 it caved in on it self. It looks like a gross flaky gray pastery. You could see flames from the organics continuing flame off. I shut it down at this point. Why waste the power?

Oh, and man it reeked. Fennel does not burn nicely. Maybe THAT's why sawdust is the normal solution.

It's cooling. There is a red hot core still. I'm holding out hope that has consolidated into something.

Well, this should be interesting ... I'm not even going to begin to speculate until I can see it up close.

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