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Re: Vermiculite+portland cement to make fire bricks? What is fire clay?
"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."
Bob,
Clay which is unfired can turn back into mud if it gets wet. it needs to be fired to 573 C before it becomes permanent and you'll never get it that hot in the chimney alone. You can try doing it yourself in a campfire or sawdust kiln, but it is tricky and prone to blowing and cracks as well as being not fired particularly high enough (typically a sawdust firing will be in the region of 600C) to make it sufficiently hard and durable. Should be taken to over 1000C IMO This would require a kiln. Using a castable means you don't have to fire it, although ideally even a castable is better if it is fired first.
Dave
"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."
Bob,
Clay which is unfired can turn back into mud if it gets wet. it needs to be fired to 573 C before it becomes permanent and you'll never get it that hot in the chimney alone. You can try doing it yourself in a campfire or sawdust kiln, but it is tricky and prone to blowing and cracks as well as being not fired particularly high enough (typically a sawdust firing will be in the region of 600C) to make it sufficiently hard and durable. Should be taken to over 1000C IMO This would require a kiln. Using a castable means you don't have to fire it, although ideally even a castable is better if it is fired first.
Dave
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