How many bags of vermiculite

[Art nj]

Hello,
I'm in the gathering stage of my barrel vault oven, and have a question on the amount of 4cu ft bags of vermiculite everyone used on their ovens. I plan on a 4" slab of vermacrete under the 32"x36" oven, plus insulating with loose vermiculite on top an the sides.
I was planning on getting 2 bags of medium #2 and 2 bags of course # 4. I'm just not sure if this is gonna be to much or not even close to enough.

Thanks
Art

[Les]

Re: How many bags of vermiculite

You will never have to much (within reason) Are you building an enclosure around it and loose fill?

[jeeppiper]

Re: How many bags of vermiculite

I ddin't use any vermiculite. I opted to use extra silicon fiber blanket instead. My fear was that small gust of wind while I was buttoning up my oven, and I would have vermiculte pellets floating around the yard forever.

[Art nj]

Re: How many bags of vermiculite

Thanks jeeppiper, that's what I may actually do.. Just buy ceramic fiber board for under the floor, and blanket on top ,back and sides of the oven.

[jeeppiper]

Re: How many bags of vermiculite

My thought was that if I ever had to go in and repair the dome, I didn't want to have to deal with pulling out all of the loose vermiculite. Why are you doing the barrel vault instead of the Pompeii dome? most folks on this forum prefer the dome over the barrel.

[Art nj]

Re: How many bags of vermiculite

I plan on baking bread and other foods more than pizza, and i like the idea of more retained heat.The build is similar enough between the both types, but I'm not doing it exactly like the Alan Scott design. I have the book bread builders and have been studying it, just gonna "modify" mine a bit. Probably just changing the insulation from under the concrete base to on top of it. My dimentions are pretty close : 32" wide on the inside- 36" deep and a dome height of 18". My original form that I shitcanned was 30"w ,36"L, and a dome height of 32". I thought that it was a little to high of a dome so I "sqooshed" it down and made it a bit wider and a little lower. Do these numbers sound right you think?

Art

[Art nj]

Re: How many bags of vermiculite

I also had an idea I like to see what others thought... I work with a lot of sheet metal in my business (signs), and was thinking of putting a sheet of bare aluminum between the insulating layer below the firebrick floor and the concrete as a break. I may actually be able to bend a pan to make an air gap between the layers. The more I think about it the more I think I'm gonna try it, maybe put holes in it in case of water intrusion, if I do bend a pan, it'll obviously need bracing inside. I'll see if I could come up with something and I'll post a picture.

Art

[boerwarrior]

Re: How many bags of vermiculite

Art,

you are going to need better insulation than a sheet of aluminum under the firebrick... In an earlier post you said you were going to use CF. Did you change your mind?

[Art nj]

Re: How many bags of vermiculite

I said between the insulation layer and the concrete base... I'm probably going with ceramic fiber board under the firebrick floor.

[boerwarrior]

Re: How many bags of vermiculite

My apologies! I read too fast!

Just remember that there will be a lot of weight on the floor so if you have an air gap with bracing makes sure it can take the weight without flexing the ceramic fiber board

[Art nj]

Re: How many bags of vermiculite

No problem, I know, I'll see what I could come up, we have a lot of u channel laying around that I could use, I think that would work best for support.. If I have the flat part of the channel facing up, and just lay them next to each other and weld them together,
It should definetly work. These are all just thoughts at this point, but it seems as though it would isolate the insulation from the concrete slab.
Art

[boerwarrior]

Re: How many bags of vermiculite

very, very little heat makes it through the 3 inches of Ceramic fiber Board under the firebrick in my oven (I was able to get my finger under the board when my oven was fired up, before I enclosed the dome) - so if the goal is to gain more heat insulation you probably don't need it.

But sounds like it will work!

[jeeppiper]

Re: How many bags of vermiculite

I don't understand the aluminum idea...I think if you have 2" thick of ceramic fiber insulation underneath the firebrick, it will take a lot for the heat travel through the CF to the concrete. Putting aluminum between the concrete and the ceramic fiberboard wont really do much in terms of heat transfer....it wont hurt, but it wont really help either. Just my opinion...

[Art nj]

Re: How many bags of vermiculite

I guess I'm just thinking too much... I'll put my thoughts into something more important like holding the heat in the dome.. Ummmm vault.
Art

[GianniFocaccia]

Re: How many bags of vermiculite

I have 2" of CF board under my floor and 3.5" of vermicrete under the board.

I like the idea of propping up the insulation and floor above an air gap using U-channel especially with a heavy Alan Scott design. Wish I'd thought of it.