Insulation question walled oven

[mitrakaas]

Hello - First time post. Some great information on the forum. Trying to get confirmation from the experts. Currently finishing a build of our outdoor brick oven. Decided to box in the system, insulated the igloo with 2"-3" of CFB and wondering if filling the remaining cavity with dry vermiculite is still the optimum way or are there better solutions. I have also read others using sand as a filler but from what i've researched, sand is an insulator. Thank you for your time.

[dakzaag]

Sand is not an insulator, just to be clear. Since you have 2-3 inches of Ceramic Fiber Blanket on top of the oven, you are asking what else to finish the insulation process. Because you have an enclosure, relatively cheap vermiculite would be easy to pour into the enclosure and be effective at increasing the insulation value. Perilite is another simple and cheap option that is available at about the same price point.

I personally like to render the outside of the dome with an insulation mix of 1 Portland or Hydrated Lime to 5 insulation mix (1/2 vermiculite:1/2 Perilite.) Even though you have an enclosure, this helps keep rodents from nesting in the insulation and gives the insulation some protection from other issues such as birds or bugs. Add water to make the blend moist and spread on the dome with trowel like frosting a cake. The mix needs to be wet enough to be sticky and putting a stucco wire mesh on first helps the stucco to grab. The wire can be a pain, but it really helps give the stucco a place to bite. Other wise you are trying to stucco onto the CFB and it rolls right off.

If you already have the dome enclosed, then the stucco is a big challenge to squeeze in there and probably not worth it. Just get a few bags of insulation and pour it in. Make sure the oven is completely dry and the enclosure is water tight before adding the insulation, so waiting a few months is not a bad idea.

[RandyJ]

I filled the whole inside of my oven enclosure with vermiculite. If I ever build another oven I will do the same thing again. I have some pretty impressive heat retention and with the door on it will take over 10 days to cool below 100F.

Randy

[mitrakaas]

Thank you both for the responses and dakzaag for clarifying the sand concern. I have not enclosed the dome yet, so I certainly will take your advice on adding the insulation mix; never crossed my mind regarding rodents, etc.. Thank you for pointing that out. I will fill the remaining cavity with vermiculite, roof it and let the games begin!!

[Danieltp]

Had the same question in my mind. Any specific brand of vermiculite? I googled them up, and see that they're normally used for gardening. Is this the same thing?

[mitrakaas]

DanielTP - I purchased insulation grade vermiculite, not the horticultural grade. Link below to where I purchased.

http://www.associatedbag.com/ShowPro...tegoryID=2547#

[Neil.B]

Some vermiculite is used for chimney insulation/fire prevention when using a chimney liner.
I bought 600lt (same price as 100ltr) of Micafil for filling the void around the oven.