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Old 05-26-2013, 02:06 PM
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Default fibre blanket under vermiculite heart?

I'm looking at a kit oven with a 50mm hearth fabricated from fire clay. The supplier told me to put down a 100mm vermicrete slab underneath the base. Is this the best type of construction? They supply fibre blanket for insulating the dome. I'm wondering should I put a layer of his underneath the vermcrete slab or would this be pointless?
Thanks

Richard
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Old 05-26-2013, 03:05 PM
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Default Re: fibre blanket under vermiculite heart?

The blanket is for insulating the dome - it will not support the weight, they make an insulating board for that. 100mm of vermiculite would work, personally I would kick it up to 127
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Old 05-26-2013, 03:16 PM
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Default Re: fibre blanket under vermiculite heart?

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Originally Posted by Les View Post
The blanket is for insulating the dome - it will not support the weight, they make an insulating board for that. 100mm of vermiculite would work, personally I would kick it up to 127
Thanks Les, ill just increase the vermiculite layer then. Is it simply a case of 'the more the merrier'? Should I put in a 150mm vermicrete slab?
Also, does this stuff strengthen as quickly as concrete? Can I start building on it the day after I pour?
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Old 05-26-2013, 04:25 PM
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Default Re: fibre blanket under vermiculite heart?

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Originally Posted by RichC View Post
Thanks Les, ill just increase the vermiculite layer then. Is it simply a case of 'the more the merrier'? Should I put in a 150mm vermicrete slab?
Also, does this stuff strengthen as quickly as concrete? Can I start building on it the day after I pour?
Insulation never hurts - there will be a point of no return but I have no clue where that is. I did not use it for my base so I need to defer the answer for someone who knows for sure. I would guess that you would want to wait about a week before you start building on it - it's pretty weird stuff to work with.
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Old 07-30-2013, 06:27 PM
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Default Re: fibre blanket under vermiculite heart?

Hey Rich you asked if the vermicrete would strengthen like concrete which leads me to belive you may just freak out when you start mixing and placeing it.This will not at all be like concrete.Think off it like a million little styrafoam beads held together with mud.When you mix it for the first time you'll think "This cant be right"but it works.It will fell spongy and strange.Win it dries its still actually soft or atleast soft compared to concrete.By the way its mixed by volume so get you a one gallon bucket to load your wheel barrow.8 buckets vermiculite to 1 bucket of mixed portland or whatever ratio your directions call for.Mix gently with a spade shovel and your gold..


Bill
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Old 07-30-2013, 06:40 PM
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Default Re: fibre blanket under vermiculite heart?

More is better, I have 2.5 inches of 7-1 vermicrete under 2 inches of ceramic board and my wood bin ceiling still gets to 25-50 degrees over ambient air temp. I wish I had gone with another 2 inches of insulation, either ceramic or vermicrete. In the winter it can be 100F over ambient.... -20F outside and +80 under the oven.
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Old 07-30-2013, 09:54 PM
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Default Re: fibre blanket under vermiculite heart?

Thx guys. Tx, ill try not to freak out. Might try an get some vermiculite mixed today. I intend using 6:1 by volume in the base, mixing dry vermiculite and dry cement and then wetting. My hearth insulation will be 135mm thick. Thanks for heads up. It's quite windy here and the vermiculite seems quite light. My biggest worry will be tring to stop it blowing away I think.

R
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Old 07-31-2013, 02:03 AM
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Default Re: fibre blanket under vermiculite heart?

[ATTACH][/ATTACH]The thickness of vermicrete and efficiency conforms to the law of diminishing returns. 100 mm is normal, a little more is slightly better, but a lot more of little extra value. Most builders have found a 5:1 ratio about best. More cement will make it stronger but less insulating. Less cement will make it more insulating but weaker.
Vermicrete takes up lots of water, way more than is required for the hydration process, so keeping it wet is not generally necessary, depending on the weather. Removing the water is however another problem. I did some tests about this that show the water removal is pretty slow. Once you've covered it over the weather won't dry it much and it will take lots of fires to eventually dry it.
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File Type: zip Vermicrete insulating slab copy.doc 2.zip (73.2 KB, 32 views)

Last edited by david s; 08-08-2013 at 12:20 PM. Reason: Typo
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Old 08-08-2013, 10:49 AM
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Default Re: fibre blanket under vermiculite heart?

Hi David, your zipfile appears to be corrupted. Could you re-upload please?

Thanks

Richard
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Old 08-08-2013, 12:24 PM
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Default Re: fibre blanket under vermiculite heart?

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Originally Posted by RichC View Post
Hi David, your zipfile appears to be corrupted. Could you re-upload please?

Thanks

Richard
works ok for me. Try this one.
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File Type: zip Vermicrete insulating slab copy.doc.zip (73.2 KB, 35 views)
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