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Old 07-22-2009, 07:24 AM
Nabber86's Avatar
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Default Hearth Insulation FB Board / Vermicrete

I poured my hearth structural layer last weekend and it turned out perfect. 4” of heavily reinforced (1/2” rebar on 6-inch centers plus wire mesh) 5500 psi concrete. Now I am getting ready for the insulating layer. I have already purchased 5 cubic feet of vermiculite and was planning on mixing up some vermicrete next weekend. However when browsing the Forno Bravo store for supplies, I ordered three sheets of 24”x36”x2” FB Board ($ouch$). So the question is…..

Should I go with just the FB Board or do I need to put a thin vermicrete layer (1” to 2”) on top of the FB Board? Not necessarily for extra insulation, but to fill the gap between the edge of the FB Board and the edge of the hearth. As shown in attachment:
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Hearth Insulation FB Board / Vermicrete-hearth1.jpg  
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  #2  
Old 07-22-2009, 03:49 PM
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Default Re: Hearth Insulation FB Board / Vermicrete

Unless you don't have enough board to go under your oven, there's no need to fill around the insulating board with vermiculite concrete. The goal is to completely surround your oven with insulation: additional outboard from the oven/insulation profile won't do any good.
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Old 07-23-2009, 08:59 AM
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Default Re: Hearth Insulation FB Board / Vermicrete

I guess the question that I am asking is does it have to be one (FB Board) or the other (vermicrete)? Does anyone use vermicrete over FB board?
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Old 07-23-2009, 09:19 AM
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Default Re: Hearth Insulation FB Board / Vermicrete

Hey Nabber,

A few builders have done that, though it might be overkill -- plus you have to work with two materials. If you are really serious about floor insulation and plan on having really, really long parties, you should put the FB Board on top of the vermiculite, as it is the more efficient material between the two.

Still, for most cases, the standard 2" FB Board is more than enough insulation, and is roughly equal to 4" of vermiculite concrete.

James
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Old 07-23-2009, 09:40 AM
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Default Re: Hearth Insulation FB Board / Vermicrete

I used the 2" FB board on my oven build - it works great! Easy to cut and I was able to start placing my oven floor bricks immeadiately after installaion. No need to wait for Vermicrete to cure.

I covered the oven with the FB ceramic insulation (had enough for 2 layers). Then poured loose Vermiculite in after I finished the enclosure so the entire oven is wrapped in an insulation cocoon.

Christo
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Old 07-23-2009, 10:28 AM
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Default Re: Hearth Insulation FB Board / Vermicrete

OK thanks.

I guess that I have been stuck on the vermicrete idea for such a long time (poured my foundation last September) that when I switched gears to thinking about FB Board, I was temporarily confused. THe FB Board should be here this Saturday. I cant' wait.
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Old 07-27-2009, 09:01 PM
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Default Re: Hearth Insulation FB Board / Vermicrete

If I were to build my hearth again, I would use 3-4 inches of vermiculite, covered with a 2 inch FB board.

Stephen
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