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Balty Knowles 06-28-2007 05:23 PM

No space for Insulation
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When I designed my base I was thinking 39" floor. After the base was finished I figured bigger is better & built a 42". Now it's time to face the consequences. The dome missed the center of the stand by an inch & at the narrowest point I only have 3" left for insulation, I've already reduced the thickness of the outside wall to a brick & a half & cant go any more.

Couple of questions

If I stuff more thermal blanket into the available space it will be compressed does anyone know if this will seriously reduce the insulative properties.

i.e. Am I better off with 2" of Insulfrax & 1" of vermiculite or with 4" of insulfrax stuffed into a 3" gap?

dmun 06-28-2007 07:11 PM

Re: No space for Insulation
The refractory blanket is about twice as good an insulator than the vermiculite/perlite concrete. If space is an issue, use the blanket.

Also, heat rises. A little extra insulation on top is more effective than on the side. Think about your house with the three-and-a-half insulation in the walls and the six inches in the attic. Same principle.

About compression: I found it's pretty dense stuff. It's not easy to squish like the pink fiberglass.

maver 06-29-2007 06:05 AM

Re: No space for Insulation
James also pointed out here recently that insulation at the top of the dome (greater thermal differential) is more important than at the base. Three inches of thermal blanket should be adequate at the base. You might add a little more on top (or loose fill over the blanket) for the more is better approach.

CanuckJim 06-29-2007 06:50 AM

Re: No space for Insulation
Dmun, Maver,

Agreed, he should go with the blanket; the R value will be much higher than cement/vermiculite. My oven has about four inches of insulation on the sides, but about six to seven on top.


Balty Knowles 06-29-2007 07:49 AM

Re: No space for Insulation
Thanks agian, much relief. I have plenty of space once I get higher than the soldier course at the base.:)



telehort 06-29-2007 09:24 AM

Re: No space for Insulation
Not to hijack your thread Balty, but I am running up on the same issue and looking for some advice. I have a 42" oven and only have a few inches of space as well. I have purchased 2 boxes of ceramic insulation and am wondering if I can get 3-4 inches around the oven if there is any need for any vermiculite/cement mixture over it or if 4 inches of ceramic is enough and I can just stucco on top of that.
Any thoughts are appreciated.

nissanneill 06-30-2007 04:00 AM

Re: No space for Insulation
Balty and Telehort,
I skimped a little and only used a 1" thermal blanket instead of 2" and then put 3 x 1" layers of vermiculite cement over that and topped it off with a 3/4" waterproofing render on top,
After drying out the dome and then 3 cook-ups with very hot fires, NO HEAT was felt what so ever at all on the top of the dome. That ha sproved to be ample insulation.
Check out the pics at:


Balty Knowles 06-30-2007 06:34 PM

Re: No space for Insulation
Thanks Neill,

Makes me feel more comfortable. I just order a bunch of Insulfrax should have enough for at least 3 layers with plenty spare to put extra on top.



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