Homebrew mix 3:1:1:1

[johnv]

Is the Homebrew mix 3:1:1:1 a good choice to use in a self sustainable structure?

I was thinking of an half barrel 16"x16" Pizza oven, and use only the Homebrew mix 3:1:1:1

Thanks

John

[Freelance]

I'm considering the same, 3:1:1:1 as inner core 2" and vermiculite/portland 5:1 as an outer layer 4". Cast on a pilates ball, what will you use as support?
From my research so far the recommendation is to go with vermiculite/portland 5:1 directly and plaster on top.
I'm still researching so I hope its OK to follow this thread for replies I hope someone with more experience provides better answers.

[UtahBeehiver]

I suggest you look up DavidS threads, he is our casting expert. He prefers the use of a sand mould over excercise ball for various reasons. 5 to 1 over is too rich for insulation on the dome more like 8 to 10 to 1 but okay for a base support.

[david s]

There are two big problems with an exercise ball. Firstly, some time consuming formwork is required because you are only casting the top half. Secondly, because of this set up the casting will have to be lifted and placed either on the insulation or brick floor. The casting will be heavy and subject to damage as well as not being a perfect fit. The sand castle method allows casting in situ without moving, seating or sealing problems and requires no formwork.
A 5:1 vermicrete or perlcrete is recommended for insulation under the floor as anything weaker is not considered strong enough to support the weight of a heavy oven. Over the top however you want to maximise the insulation value, but still maintain enough workability and strength to work as a substrate to take the render layer over it. (see Utah's table of strength/K values) I find around 10:1 produces adequate strength and just enough cement to make it workable. If you throw in a handful of powdered clay for every litre of cement it improves the mix markedly.

[Freelance]

Thanks David and UtahBeehiver for your clear and specific answers, all remaining for me is to learn how to make the sandcastle form, I'll continue my research on that topic.
What a great forum this is!