Vermiculite+portland cement to make fire bricks? What is fire clay?

[apples]

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

[david s]

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.

[apples]

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

[david s]

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.

[apples]

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???

[david s]

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.

[apples]

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

[david s]

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.

[apples]

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.

[david s]

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.

[apples]

Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

Yeah that is pretty much what I found in the net. YOu can use 0.8mm but it is not as effective as the 0.5mm. They call 0.5mm premium and 0.8mm economy. More fibres wiht the smaller diameter.

Anyway I will definantly now be using some of my 0.9mm stainless wire. Hey, it's gotta do something, better than not having it.

Have you ever used from claypave Rylbond mortar (1450). Would be nice to use this for say 20mm wall thickness. It says it air drys but is only a cement for small thin applications.

Surely there is a product that I can just use to make a 20mm thick or what ever thick wall with out it cracking, or needing to be fired properly in an oven?

And if I used fire bricks are they easy to cut?
Can you tie them together?
I have a price list from claypave but I don't know if they are for insulation type fire bricks or for themal heat holding type bricks.

[azpizzanut]

Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

Hi All,

I have one of the Aprovechio rocket stoves that I bought at a store that sells preparedness supplies. They have canned, dehydrated foods and solar ovens too.

You Tube has lots of information on rocket stoves and you can Google for information too. Mine is made of refractory clay but you can make a rocket stove of nothing more than stacked fire bricks or red bricks. Sometimes a temporary stove made of stacked bricks is efficient and economical depending on the needs of the moment.

If you plan on using a small rocket stove then maybe making the hot face from Raku clay would work ok. It is strong and easily available from a ceramics shop. Also consider "paper clay" it has cellulose fibers in it and it also can be fired at low temperatures compared to other types of clay. You can insulate around the "chimney" with a variety of things including wood ash, ceramic blanket, vermiculite and perlite. Mix up some vermicrete or perlcrete for a top layer, install bolts or pieces of rebar for the pot to stand on and you're in business.

Cheers,

[david s]

Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

"Surely there is a product that I can just use to make a 20mm thick or what ever thick wall with out it cracking, or needing to be fired properly in an oven?"

I was planning on using a dense castable (Caldreys Castflo 1450) and mixing about 25% perlite into it, then outside that using 2" perlcrete 10:1 then outside that a 10mm ferrocement outer shell.
But there are many ways it could be done, just depends what you have access to.If you know anyone with a kiln you could design it in pieces and have them fired.

[azpizzanut]

Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

Hi David s,

Calderys website lists no less than sixteen "dense" castables and five insulating castables. Is there a reason you would mix insulating perlite with a dense castable? It seems the castable would be much more resilient and long lasting without an admix of insulation.

Apples,

Cracking is not an issue with the rocket stove. If it can be made with stacked bricks with their inherent spaces between then a crack in the chamber is nothing to worry about. Also, I am not sure that a clay chimney needs to be fired "properly" in a kiln since the example I saw was simply dried completely then heated using a wood fire. In this example the level of firing from the wood was adequate to harden the clay for its intended use as a fire chamber for a stove. Ideally though, if you have access to a kiln then you can be assured it was done professionally. However, for the cost of raw materials involved I'd go with doing it yourself. You can even fire clay the old fashioned way by putting the piece in a fire pit. Look here:

Pit fired pottery - Wikipedia, the free encyclopedia

Claystation Technical

Cheers,

[david s]

Re: Vermiculite+portland cement to make fire bricks? What is fire clay?

[QUOTE=azpizzanut;118550]Hi David s,

"Calderys website lists no less than sixteen "dense" castables and five insulating castables. Is there a reason you would mix insulating perlite with a dense castable? It seems the castable would be much more resilient and long lasting without an admix for a stove."

I agree, but you don't really need that thermal mass for a rocket stove, that's why I was intending only adding a relatively small proportion of perlite so the mass is reduced while the strength not too compromised. Another reason I was planning on using the dense castable and "adjusting" it is because I have it on hand and use it all the time.