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Old 05-04-2012, 11:42 AM
Xene's Avatar
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Default Hearth floor and vermiculite question.

We got the concrete floor poured this morning so now we are on to the vermiculite layer but I'm having trouble pin pointing exactly what I need. What we have available in this area is used for attic insulation, labeled as micaflake in a 3-cubic feet bags. How much do we need for 5' x 5' x 4' (7.5 cubic feet) area - at what ratio? I am finding the Pompeii instructions a bit vague in the mixing ratio suggestions. I think we need 3-4 bags of vermiculite to compensate for the compaction mixed at a 1 bag vermiculite to one 94 lb bag of Portland. Am I aiming straight on this?

The other question I've got then is that the instructions state 'oatmeal' consistency - is that thick oatmeal or with cream?

Thanks for the help!
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Old 05-04-2012, 11:47 AM
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Default Re: Hearth floor and vermiculite question.

Oh, and knowing how everyone likes lots a pictures, here is what we started with this morning. The concrete pour went well except that my little mixer died half way through and we had to take it apart to fix it. Will be returning the little red version for a more heavy duty version at the end of this day. (Who knew I'd be so hard on a concrete mixer?!)

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Old 05-04-2012, 02:49 PM
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Default Re: Hearth floor and vermiculite question.

I'd figure 5-6 bags to account for the shrinkage you will see once you wet the vermiculite. I've built a few ovens and have found the required volume x 2 will get the job done with a little extra. As for consistancy, you want it to hold its shape when you form a ball in your hand.
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Old 05-04-2012, 04:00 PM
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Default Re: Hearth floor and vermiculite question.

Quote:
Originally Posted by Xene View Post
We got the concrete floor poured this morning so now we are on to the vermiculite layer but I'm having trouble pin pointing exactly what I need. What we have available in this area is used for attic insulation, labeled as micaflake in a 3-cubic feet bags. How much do we need for 5' x 5' x 4' (7.5 cubic feet) area - at what ratio? I am finding the Pompeii instructions a bit vague in the mixing ratio suggestions. I think we need 3-4 bags of vermiculite to compensate for the compaction mixed at a 1 bag vermiculite to one 94 lb bag of Portland. Am I aiming straight on this?

The other question I've got then is that the instructions state 'oatmeal' consistency - is that thick oatmeal or with cream?

Thanks for the help!
I used a 7 to 1 ratio under the oven and then aaed a 2 inch FB board.

Do not worry about buying to much vermiculite as you can use the extra later as poured in insulation around your oven after the dome is completed.

I went back to the landscaping store 2 more times to get more after completing the dome

For a 7 to 1 mix it is by volume, I used a plastic tea pitcher to get the volumes, I wet the vermiculite and then added the Portland as a wet slurry mixing with a small shovel.

Chip

Last edited by mrchipster; 05-04-2012 at 04:08 PM.
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Old 05-04-2012, 05:53 PM
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Default Re: Hearth floor and vermiculite question.

We ended up using 3.5 bags each of vermiculite and Portland. That job was the worst of them thus far. Mixing these two together was not the least bit enjoyable - ha - in comparison to regular concrete that is, but it looks nice and level and I'm really anxious now to get going in my fire brick!

Thanks for you replies, greatly appreciated.
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Old 05-04-2012, 06:08 PM
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Default Re: Hearth floor and vermiculite question.

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That job was the worst of them thus far.
Wait till you get to the last 4 chains of the dome... That is where the fun realy starts.

Chip
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  #7  
Old 05-05-2012, 07:42 AM
Journeyman
 
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Default Re: Hearth floor and vermiculite question.

Something seems off. A bag of Portland is about 1 cubic foot. If your vermiculite is 3 like you said that means you used a ratio of 3:1.
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Old 05-05-2012, 08:06 AM
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Default Re: Hearth floor and vermiculite question.

Augh! Numbers are not my strong suit- in fact I'm a bit math dyslexic (artist) so I let the husband take charge of my ratios. I asked here to double check his figures, and now in asking him again, he thinks we did do 3:1.

Okay, now what can I do? Will the base be okay with that ratio? Do I need to buy FB board to compensate for our mistake? [Shaking head] I knew something was amiss.
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Old 05-05-2012, 09:33 AM
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Default Re: Hearth floor and vermiculite question.

Before you get too worried, what size bags of Portland did you buy? 98 pounds are pretty standard, but if you used the smaller half sized bags you would be at 6:1.

If you are at 3:1 I would personally find a local refractory dealer and Put a couple inches of board on top of it.
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Old 05-05-2012, 11:06 AM
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Default Re: Hearth floor and vermiculite question.

Yes, I too had hoped that we didn't make that mistake...but I believe it was the size of the pre-mix cement bag that threw off our calculations. In the excitement of getting it done we didn't factor in the bigger size of the bag (and to add to it, we had my brother-in-law pick them up for us and didn't figure in the size difference!)

There is a product a brick yard in town carries called Insul Cast Delta Crete. Could we pour a layer of this under the oven floor - hopefully about 2-inches thick - that would work?

The FB board adds another $200 to my oven cost. Sick about it.
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