#11  
Old 07-14-2010, 02:12 PM
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Default Re: Medium vs Fine grade Vermiculite?

Im not one of the experts, but as far as i was aware you lay a 4 inch structural hearth (pure concrete) and then lay a 4 inch insulating hearth by mixing the vermiculite with the concrete on top of that.

Cheers Ross
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  #12  
Old 07-14-2010, 03:30 PM
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Default Re: Medium vs Fine grade Vermiculite?

Quote:
I have heard two stories. First you put Vermiculite and then on top the cement.
This approach has been entirely discredited: This leaves entirely too much thermal mass inside the insulation envelope. Support slab first, then insulation, then brick hearth.

Four inches of vermiculite concrete, top and bottom, is the minimum. The stucco coat is for waterproofing/finish. You don't want to seal the dome right away, do your curing fires first to drive most of the water out of the insulation. Vermiculite concrete absorbs a LOT of water.
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  #13  
Old 07-14-2010, 07:19 PM
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Default Re: Medium vs Fine grade Vermiculite?

So one has to wait until the 4" cement slab cures before pouring in the 4" vermiculite?

So the 2x6s used to form the cement slab are removed and then placed on top of the cured slab and vermiculite poured into it.

I am just trying to document the steps.
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Old 07-22-2010, 04:23 PM
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Default Re: Medium vs Fine grade Vermiculite?

with regards to a hearth slab which is say 4" or 100mm,half can be concrete and the top half can be a mix of vermiculite with portland cement,this is amble.then toped with fire bricks it will be 8" inches of thermal mass,cant get any better than that.
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Old 07-23-2010, 10:19 AM
Peasant
 
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Default Re: Medium vs Fine grade Vermiculite?

Thanks.

How about the cladding on the dome. Same thing. 2" vermiculite/portland cement and 2" concrete on top?
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Old 07-23-2010, 10:30 AM
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Default Re: Medium vs Fine grade Vermiculite?

"Same thing. 2" vermiculite/portland cement and 2" concrete on top?"

No.

The suspended structural slab should be 4 inches of reinforced concrete. Then 4 inches of vermicrete (5:1 mix) on top of that, then the hearth bricks. The insulation layer over the dome should be 4 inches of vermacrete (12:1 mix).

You can start with the vermacrete over the structural slab after one day. Keep the structural slab (and subsequent vermacrete layers) continuously wet for at least seven days - preferably longer.

Last edited by Neil2; 07-23-2010 at 10:34 AM.
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Old 07-23-2010, 11:07 AM
Peasant
 
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Default Re: Medium vs Fine grade Vermiculite?

Thanks Neil;

Do you put the 4" Vermiculite on the base slab in one application? Or several applications?

The vermiculite on the dome, can you put stucco on top of it? I never dealt with Vermiculite before. Does it harden?
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Old 07-23-2010, 01:58 PM
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Default Re: Medium vs Fine grade Vermiculite?

Quote:
Do you put the 4" Vermiculite on the base slab in one application? Or several applications?
You can do both layers at once, No need to let the support slab set, even. It's the same stuff as the structural concrete, just a different aggregate. Most people do it in two batches, because it's a lot of work for one day.
Quote:
The vermiculite on the dome, can you put stucco on top of it? I never dealt with Vermiculite before. Does it harden?
In the course of a week the vermiculite concrete sets to a cork like consistency. It will be crumbly at the edges, and for this reason you may not want to have it exposed on the exterior of your structure. You can put stucco directly on the cured and dried vermiculite concrete. It's suggested you wait a month or so for this step to assure your dome and insulation is dried through.

Please ignore the poster above who suggests two inches of concrete and two of vermiculite concrete under your oven floor. This is half what you need of both.
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Old 07-23-2010, 05:41 PM
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Default Re: Medium vs Fine grade Vermiculite?

yea mate,make sure the dome is well mortared,as in the gaps around the bricks are all filled,next thing is mix the vermiculite with portland cement i use a mix of 5 to 1, 5 vermiculite to 1 cement,mix till it is a oatmeal consistency,just so it holds together,or you can put the vermiculite only in mums old pantyhose legs and wrap around the dome like a sausage,you will need about 10 legs to do this,then pat it down so it is about 40-50mm thick,then appy chicken netting and then mortar and then render with a final coat,
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  #20  
Old 07-25-2010, 09:26 AM
Peasant
 
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Default Re: Medium vs Fine grade Vermiculite?

Thank you so much. I live in Michigan and looks like you are in Jersey where the climate is similar. I started the excavation this week. The city inspector told me to dig 42" deep footers for the oven support. It is a lot of work but work is underway. Not sure if you had to do the same for your oven. Maybe it is overkill, but sounds like I need to go below the frost line to ensure the slab is not lifted in the future.
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