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130mountainside 09-20-2009 05:29 PM

Vermiculite/ cement- set?
I poured the 4" layer of 5:1 vermiculite/ Cement mixture. I mixed it to the consistency of oatmeal- dryer than cement. After 24 hrs. it is still not set....any suggestions?



Les 09-20-2009 05:53 PM

Re: Vermiculite/ cement- set?
What do you mean by not "set"? Is it dry? I didn't go that route but to my understanding - it will not be a solid, it will have some compression.


Neil2 09-20-2009 07:26 PM

Re: Vermiculite/ cement- set?
Keep it damp. It will take up to 6 days to set enough to load.

130mountainside 09-21-2009 06:02 AM

Re: Vermiculite/ cement- set?
By "set" I mean hard- like cement. will it always be 'spoungy'

egalecki 09-21-2009 09:32 AM

Re: Vermiculite/ cement- set?
It will never be like plain cement. It will be sort of spongy- sort of like cork. It will also crumble around the edges if you mess with it- I know it seems as though it will never be suitable, but it does work. I have several inches of it under my dome, and it's never compressed at all- but it was a major leap of faith to go ahead and trust it!

130mountainside 09-21-2009 11:22 AM

Re: Vermiculite/ cement- set?
I decided to minimize the amoutn of space covered to 2" beyond the hearth foot print and am using a round form to create the round shape---I am thinking that I never want to remove it for fear over time this 5:1 mix may dust. PS my vermiculite is not the 3/8in size but the 1/4 to 1/8 size.....see any problem permanently leaving the frame or the 1/4 size verm.?


dmun 09-21-2009 12:04 PM

Re: Vermiculite/ cement- set?
Is your form wood? I'd stay away from combustibles here - not every oven avoids cracks. Your vermiculite concrete may be a bit crumbly around the edge, but it isn't going to collapse.

Your vermiculite size is fine.

kebwi 09-21-2009 12:20 PM

Re: Vermiculite/ cement- set?
What about the really fine perlite, about the consistency of laundry detergent? I posted a question about it this morning but haven't received any responses (my post's verbosity may have scared off potential readers/repliers). Is that too fine to make good insulation? I already wrote this in the other thread but my concern is that it will pack too tightly and won't leave any voids for air...which is the critical function of any insulation of course. Would the answer differ depending on loose-fill vs. permcrete or do you want the same grain size (whatever "right grain size" means, large or small) regardless of whether you are loose-filling or making 'crete?


Neil2 09-21-2009 12:48 PM

Re: Vermiculite/ cement- set?
Go for a courser perlite. Better insulation value.

kebwi 09-21-2009 01:03 PM

Re: Vermiculite/ cement- set?
Thanks Neil2.

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