Insulating the dome

[antwlo]

I'm at a a point in my build to start thinking of how to insulate my dome. My plan is to cover it with 2" of ceramic fiber blanket. However, reading the many threads on this forum, I noticed that some builders put a layer of vermiculate/cement before the blanket.


So I'm thinking of the following... layer of Vermiculate and cement--> 2" of CFB --> Another layer of Vermiculate/cement?


Is this recommended or is it an overkill?

[UtahBeehiver]

Are you building a igloo or an enclosed oven. P ro V crete are used for two reasons, insulation and shape or both. If you are doing a igloo then P or Vcrete AFTER the blanket to shape the oven into the final shape (as lean as 8:1) and for stucco or the final outside covering base structure, If you are doing an enclosure, you can pour dry vermiculite in the enclousre "AFTER" the blanket. 2" of CF blanket is the bare minimum insulation. The FB kits have 3". If you do a search on v or pcrete you will see it holds a lot of water and care must be taken to get it all out before curing.

[antwlo]

Thank you for the response.
I'm going to build an igloo style oven, not enclosed.

Sorry for what might seem a sill question...but... is Pcrete the same as Perlite, and Vcrete the same as Vermiculite?

Based on what you suggested...I should put P or Vcrete after the CFB, right? how many inches thick on top of the blanket should I do?

As for 2" or 3" CFB, I can easily get another 1" and add it since I'm not at that stage of build yet.

[JRPizza]

The "crete" in Pcrete and Vcrete is portland cement mixed in with the insulating perlite or vermiculite to hold it together and give it some strength. Do a forum search and you will find ratios to do your mix and some hints. I think david s is sort of an expert on the stuff.

[UtahBeehiver]

Here is a link to one of the across the pond builds who just put vcrete over CF blanket. He did a very good job. You do not need to go to this extent of a template for the vcrete but it is helpful if you can do it. A 8:1 v or p crete ratio gives you almost thermal characteristics as CF blanket. So if you go this route you can get buy with 2" of CF and 2" or so of V or Pcrete.
https://community.fornobravo.com/for...an-build/page9

[antwlo]

Thank you for the advice. Based on what you said, would it be better to add another 1-2" of CFB and finish with a stucco layer, or stay with 2" of CFB and 2" or more of vcrete?

[UtahBeehiver]

up to you.