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Old 10-27-2010, 02:51 PM
GFW GFW is offline
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Join Date: Oct 2010
Location: Eastern North Carolina
Posts: 6
Default Hearth insulation layer

Hello all, working on foundation for an earth oven, up to the insulation layer for the hearth and had some questions,

Just wanted be sure I understood the mix. Portland cement and vermiculite mixed ratio of 5 or six to one, (I assume the measure is by volume in dry state for both) nothing else added like sand or rock. Also, I read one of the threads where someone had better success by mixing the Portland cement separately into kind of slurry and adding it to the vermiculite in a separate container than mixing into kind of an oatmeal state. Oh, how about the reinforcing rods, I am pouring a 6.5 diameter circular base, seems some say rods on 12 inch centers and others on 8 inch centers. Or can the wire screen be substituted.

Thanks for the advice!!
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Old 10-28-2010, 05:12 PM
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Il Pizzaiolo
 
Join Date: Oct 2006
Location: Vancouver Island
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Default Re: Hearth insulation layer

six to one is fine. No sand or gravel. Mixing a slurry first is simpler. When mixing the vermiculite and cement - mix gently (by hand not machine) so as not do break down the vermiculite particles and reduce insulation value.

For rebar in the suspended slab, I suggest either 8 inch spacing for 1/5 inch diameter rebar or 6 inches for 3/8 inch rebar (the 3/8 is much easier to work with). Both ways, in a grid. Re-bar is cheap. Wire mesh (WWF) should not be substituted for rebar.
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