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Old 08-03-2011, 05:54 AM
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Default Vermiculite+portland cement to make fire bricks? What is fire clay?

Vermiculite+portland cement to make fire bricks?

If you mix vermiculite and cement at say 5:1 can it be cast and set into bricks? Can those bricks then be used right in the fire front? I think I read that the cement stuff breaks down and then the whole lot will fall apart?

What is fire clay exactly? Could I line the inside with fire clay then backfill with the vermiculite and cemet mix?

Is that vermicultie and cement mix prone to cracking due the the heating and cooling?

P.s. this is for a rocket stove, with maybe an oven later on.

Peter
Australia
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Old 08-04-2011, 02:51 AM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

For an oven you don't want an insulating hot-face, but you do for a rocket stove.

Vermiculite and perlite are good for 1100C
.
Portland cement is no good above 300C, but lime is, although the resulting mix may not be strong enough.

You won't get fire clay to a hot enough temp to make it permanent. Your best bet would be to use some calcium aluminate cement.
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Old 08-04-2011, 03:46 AM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

I picked up some hydrated lime from bunnings today, I thought I read about that somewhere.

You say lime is good for 1100, so I can just mix up my vermiculite and hydrated lime then in to a cement mix?

You won't get fire clay to a hot enough temp to make it permanent
Permanent as in it might fall apart and crumble etc if it is not fired?

calcium aluminate cement.
So I should look for this stuff and not use the lime?

Where about's can I get the calcium aluminate cement?

Calcium is like chalk right? I watched a video where old mate mixed chalk powder with metho and then painted the inside of his furnace. I guess to protect it, reflect heat and make it pretty?

Peter
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Old 08-04-2011, 01:44 PM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

Go to a refractory supplier and tell them what you are trying to do. There are lots of products available. Try asking for a hot face insulating castable. The lime and perlite mix will probably result in a material that is too soft and crumbly, but might be worth experimenting with.The addition of sand will make it stronger, but less insulating.

Last edited by david s; 08-04-2011 at 01:46 PM.
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Old 08-04-2011, 03:17 PM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

Well I'm making a rocket stove. I was thinking of using some steel pipe or rhs for the internal passage. Then I would back fill with plain old vermiculite to insulate. The idea being that the steel will give a little thermal mass.

I did make one using 3" rhs and then put that in an old paint bucket and filled with concrete. It did work but not properly. I really need that insulation to keep the heat in. And I will use a bigger internal diameter next time.

The downside to using steel for the hot face is the expansion and contraction and the fact it will corrode/rust out eventually. The good thing though is that I can weld up a nice strong structure.

It would be nice to have a clay mix say 1/2" thick or maybe thicker that the actual fire and hot face would burn on. Then back fill with insulation mix, then a stronger clay/cement mix on the outside. I guess normal portland cement would work as by then the temperature should not be that hot on the outer layer???
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Old 08-04-2011, 08:15 PM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

I have intended to do exactly as you describe, to make a rocket stove, but as yet the plans are only on paper. I intend to use a dense castable refractory reinforced with stainless steel needles, which I use on a regular basis for other castable items, for the inner face approx. 12mm thick for strength and refractory properties. The outside shell should be fine in normal concrete as it will not get too hot.
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Old 08-05-2011, 01:35 AM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

When you say stainless needles, do you mean like knitting needles?

I sell welding supplies and I can get you stainless TIG filler rod in sizes 0.9mm 1.2mm 1.6mm or 2.4mm 316L grade for a good price on a 5kg pack.

There is a bit of a pic on this page in the green container, they are about 1 meter long. http://www.learn-how-to-weld.com/tig-welding/

Yeah I had though of stainless as well as it does not rust and should handle the heat better.

Peter
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Old 08-05-2011, 05:22 AM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

No they are much thinner. The correct name is melt extract fibres and they are 0.5 x 25 mm. Mine are quite expensive and cost me $20 /Kg after freight. Maybe you can get creative and find a cheaper substitute, but get 316 not 304, as 304 will still rust.
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Old 08-05-2011, 05:35 AM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

Hmm, I'm gunna google "melt extract fibres".

SO do you just mix it in with the mud?

I was thinking more like welding it all together like reo mesh in concrete.
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Old 08-05-2011, 05:38 AM
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Default Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

no they're mixed in to the wet mixture to give you a random distribution like mixing fibres in a concrete mix. I think that's why they are short.One school of thought is that they don't make that much difference and over time the heat will probably corrode even stainless steel.I use them because they are meant to make the castable stronger and are recommended by the castable suppliers to reduce cracks and increase strength.

Last edited by david s; 08-05-2011 at 05:43 AM.
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