I am new to this stuff, but am wanting to make a rs with a steel drum on top like a mass heater. This will be in my garden to radiate heat.
I have decided I want to cast the burn chamber and chimney out of vermiculite, but am not sure what to mix it with to stay together. It will be out of direct rainfall, but the bottom will get damp. What adhesive is recommended? Would plaster of Paris work? Thanks
Plaster would quickly disintegrate in the heat produced in the combustion core. I think refractory cement will be the only thing that will endure in your conditions. You would want to build in moisture breaks to keep the core separate from the ground... something like bricks or cement board spaced up so air can flow beneath the core, then insulated all around on top of that, above and below the core.
A great place to start is the book by Evans, "Rocket Mass Heaters." And read everything Ernie and Erica Wisner have posted here (they are soon to release a book too, and I expect that will be well worth reading too).
Your question suggests you have a great deal of reading ahead of you this summer. You have a couple good months in the summer to read everything you can find.
And I highly recommend beginning with an outdoor build, just like you are planning. We never want the rocket stove to burn itself down, but if that's what we're going to do, far better for that to be outside in the garden!
What you describe will not work. I suspect the fire riser would burn itself out, and then the heat circulation would fail. Then the fire would either become smothered, or just burn like a small fire built in the feed tube. Not terrible if outside. At best super nasty/smokey if inside, and potentially far more dangerous. Always test outside first, and be prepared to put out the fire if it gets out of control.
This is probably one of the better examples of insulated refractory casting on Youtube https://youtu.be/7ANMXGrxgnE - he describes the mix at 3.17. I've used this to build three cores (using either perlite or vermiculite) to date and they are working very well. I have molded fire bricks around the feed tube as that's where all the wear and tear happens.
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