Re: Good day from South Oz
I advised a guy to try using the home brew mortar recipe as a castable about a year ago and he's quite pleased with the result, but who knows how it will survive the test of time. My guess is that it will not perform as well as a calcium aluminate based castable. One problem is the high proportion of unfired clay in the mix, which will give you some shrinkage problems against the mould. You should remove the sand as soon as the mix is hard enough to be self supporting. This is even more important withba clay/cob oven where the shrinkage is much greater. Another problem is that the mix will take way longer to harden. Cement and lime mixed together create some chemistry that results in very slow hardening. A third problem is the unfired clay content makes slow curing to drive off water even more important to take it slow to avoid cracks and blowing. Good luck.
Dave
Ps I think Shiracete is a calcium aluminate based castable with perlite added to it to make it an insulator. This would not be suitable for an oven because you want a dense material. It is also a waste of money to use it as an insulator for an oven because it is way more refractory than you need on the outside and it's expensive. Unless some of it fell off a truck.
I advised a guy to try using the home brew mortar recipe as a castable about a year ago and he's quite pleased with the result, but who knows how it will survive the test of time. My guess is that it will not perform as well as a calcium aluminate based castable. One problem is the high proportion of unfired clay in the mix, which will give you some shrinkage problems against the mould. You should remove the sand as soon as the mix is hard enough to be self supporting. This is even more important withba clay/cob oven where the shrinkage is much greater. Another problem is that the mix will take way longer to harden. Cement and lime mixed together create some chemistry that results in very slow hardening. A third problem is the unfired clay content makes slow curing to drive off water even more important to take it slow to avoid cracks and blowing. Good luck.
Dave
Ps I think Shiracete is a calcium aluminate based castable with perlite added to it to make it an insulator. This would not be suitable for an oven because you want a dense material. It is also a waste of money to use it as an insulator for an oven because it is way more refractory than you need on the outside and it's expensive. Unless some of it fell off a truck.
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