I'm getting ready to build a
rmh to use in a
greenhouse, ideally as the platform for an aquaponics set up. The
cob platform would be roughly 4' wide by 8' long by 18" tall. What I'd like to do is put a liner we use in aquaponics directly onto the cob platform with a bit of
wood framing to hold it up. The liner would be 4' x 8' x 1' tall and would be filled with
water (roughly 32cf of water, right around 2000lbs spread over the 4' x 8' platform.
Could a cob platform support that weight? And, can I count on even
enough heat distribution so I won't melt the liner or light the wood support framing on fire?
My basic plan for the platform would be to build it on the ground, a 3" layer of sand for insulation, then 3" of cob, 6" ducting (4 runs through the platform) with cob all around it and 6" of cob on top. I'd like it to be warm on top (70-90 degrees) but never so hot it would melt/damage the liner. I'd use a wood frame to hold it all in during the forming, but I'd think to take off the wood frame after (there will probably only be 4" of cob between the side of the platform and the edge of the outside duct on both sides).
No matter how confident I am, before I put the liner on, I'll run a bunch of tests to make sure it's all working according to plan. Worst case scenario I could add a layer of bricks on top of the platform or put a layer or two of some cementaceous board to spread out the heat a bit better, but I'd like to make the cob portion as well designed as possible to get the final height to a desired level. If I need less cob, I can fill the bottom, if I need more on top to ensure no burning and even heat, I can dig down or raise the height of my bed.
Last question, in building a platform like this, I'm estimating needing around 40 cf of cob. 4' x 8' x 2' is 64 cf, - 25 cf for the duct leaves 40 cf. I could easily use some hunks of urbanite, old bricks, old cement pavers, anything to help take up space. But I'm a bit nervous about having to come up with a
yard or so of cob. Is that an awful task or not that bad?
Thanks for any input - Rick