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-   -   Vermiculite cement ratio question (http://www.fornobravo.com/forum/f8/vermiculite-cement-ratio-question-12911.html)

WoodchuckDad 05-12-2010 01:24 PM

Vermiculite cement ratio question
 
I have seen 5/1 and 6/1 suggested on this site. is that by volume? should I take a small pail and do 5 pails vermiculite to 1 pail portland cement?

Tscarborough 05-12-2010 01:42 PM

Re: Vermiculite cement ratio question
 
8/1 can also be used. I had the chart showing the properties of the various mixtures linked on a thread here a while ago. Here is another one:

http://brokebrick.com/perlite.jpg

lwood 05-12-2010 03:09 PM

Re: Vermiculite cement ratio question
 
Great info, thanks TS.

dmun 05-12-2010 03:33 PM

Re: Vermiculite cement ratio question
 
The higher proportion mixes, (I've heard as much as 10:1) require power mixing of the slurry, and adding it to the lightweight aggregate.

Thanks, Tscarborough, for that chart, which gives exact water amounts. It also confirms the 1:1 ratio between aggregate and finished volume.

kebwi 05-12-2010 04:21 PM

Re: Vermiculite cement ratio question
 
I used 5:1, 8:1, and 10:1 and didn't power mix any of it. Of course, I might have done it wrong. I put the dry materials in a garbage bag and "shake-n-baked" it lightly with a lot of rolling and tumbling. Then I poured the water in and mixed it up in a wheel barrow with a trowel and my bare gloved hands (working up to the elbows), gently mixing it all up, scraping the sludge off the bottom of the wheel barrow, and slowly infusing the mixture.

Despite a lack of power mixing, it seemed to work fine for me.

Tscarborough 05-12-2010 06:22 PM

Re: Vermiculite cement ratio question
 
Note also that unless your oven is 20 feet tall and built from solid gold bricks, your slab loading will probably not exceed 20 PSI.

WoodchuckDad 05-12-2010 06:31 PM

Re: Vermiculite cement ratio question
 
That chart threw me for a bit. I had to go back and reread a lot of things. So to clarify, I don't see sand as part of the hearth insluation layer recipe, just portland cement and vermiculite. am I on the right track?

Tscarborough 05-12-2010 06:38 PM

Re: Vermiculite cement ratio question
 
Yes, no sand needed. Perlite is an aggregate.

WoodchuckDad 05-12-2010 07:08 PM

Re: Vermiculite cement ratio question
 
how long do you wait afterpouring for it to cure before moving to the oven dome?

dmun 05-12-2010 07:25 PM

Re: Vermiculite cement ratio question
 
One week, more or less. If you pack in vermiculite on Sunday, you're probably fine to level and lay your floor the next Saturday. As Tscarborough says, even the weakest mix has lots of compressive strength for your application, so even if it isn't at absolutely full hardness it shouldn't be a problem.


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