Loose Vermiculite or Vericulite Concrete for insulation??

[BradNSW]

Tomorrow I'll finish the dome on a 40" oven and build the enclosure (54" x 54"). It is big!! Should I fill the void with:
1. Loose Vermiculite to provide insulation (without any moisture to worry about curing out)
2. Vermiculite concrete (which will have a huge amount of water, that may make curing difficult)

Additional Info:
-I'm in Loveland CO and have been using a space heater, under a tarp, for the last week to keep the mortar from freezing (lows in the high 20's) at night. The heater actually pulls out a lot of the moisture in the mortar...all is looking great. I've been misting the entire dome during the day, while I work on the next brick courses.
-I've got 5 huge bags of Vermiculite and portland cement/mortar so I can do either loose vermiculite or vermiculite concrete.

Any feedback is appreciated!!!

Photos for reference only.

[RandyJ]

You will want to put at least 2" of ceramic blanket on then if you want add loose fill over the top of that. The only reason to do vermiculite concrete is if you will have a exposed dome.

Randy

[BradNSW]

RandyJ,

Thanks. Your feedback gave me the solution I think will work best!

A combination: First a 2" coating of vermiculite concrete. Totally cure that massive dome...then fill the rest of the 54"x54" square enclosure with the loose vermiculite.

Finally, stucco over the enclosure.

Thanks again!

[rsandler]

Confirming, for your context, loose fill is going to be better than vermi-crete. Adding cement drastically reduces the insulation provided by vermiculite. As Randy says, when you're going for an igloo shape, or under the floor, there's no (vermiculite-based) option besides making concrete, but if you have an enclosure, you're better off putting it in loose.

Some on the forum have noted that loose vermiculite has comparable insulating properties to ceramic fiber blanket, so in theory you might be okay just with loose fill. The challenge is going to be getting enough insulation on top of the dome, allowing for the loose vermiculite settling over time.

Also note that those 5 huge bags may not go as far as you think. I assume these are 4 cubic foot bags. I needed about 10 of those (perlite in my case) to fill my enclosure for my 36" oven, and that was after wrapping the dome in several inches of CF blanket (perhaps going just loose fill would have done the trick, but I didn't do that). Plus I built my enclosure roughly octagonal, cutting off the corners to avoid having quite so much internal volume. Though you also seem to have very little space on your stand outside the oven, so maybe you're close (though then I'm also a little concerned whether you have room for enough insulation). Basically you need to find (interior height*width*length of enclosure) - (4/3*3.14159 * external radius of dome^3) all in inches, divide by 1728 (to get cubic feed), and see how that compares to the 20cuft of material you have.

Unclear from the picture, but I really hope you've got some insulation under the oven floor there...I guess too late now if not!

[RandyJ]

I believe i had added 10 or 12 bags on my first oven. It doesn't go nearly as far as you would think.

Randy

[UtahBeehiver]

Dry perlite or vermiculite have very good insulating K values and similar to ceramic fiber (0.0179, 0.0376 and 0.055 respectively). If you go the p or v route here are a couple hint, first, take some scrap dry wall or something similar and block off the corners of you enclosure (this will reduce filling in these area that are unneeded, second, make sure you leave an access point near the top to add additional material if it settles. Use what you have. V or P crete do not offer as much insulation as dry V or P.

[BradNSW]

Awesome feedback from everyone!! My plan on coating the dome with vermiculite concrete was more work than needed.

Thanks rsandler for explaining the loose stuff in the void will actually have a better insulation value than v-crete.

For UtahBeehiver - I will definitely use scrap that I have handy to create corner air voids and save on the vermiculite. That will help what I have go farther. I just ordered 20sqft of 1" CF blanket. From what Randy said, I may be short but maybe the blankets will help fill the void and add a higher insulation value.

For rsandler - I did put 4" of vermiculite concrete under the firebrick base...which sits on top of 3.5" of reinforced concrete.

[BradNSW]

Dome was completed on Monday. Temps in the evening have been in the high teens/low 20s. When the sun sets, I cover it with a blanket/quilt followed by two plastic tarps. I've had a small space heater inside. In the mornings, the interior is 80-90 degrees, the blanket is soaking wet from condensation and exterior of the bricks is in the 50's (IR heat gun). No sign of cracks. I keep the tarp off all day (wx in the 50s and sunny) so water can escape. Next Monday will be a week and I'll start a slow curing for a week. The exterior box is now in place (without the roof). Following the last day of curing, I'll add the insulation (a 20sqft CF blanket and lots of loose vermiculite) and add the roof. Pizza on the 30th!!