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smuth10 11-09-2008 10:32 AM

To vault or not to vault
I know this issue has come up a thousand or more times on this forum, but I got ahead of myself a little bit and now I am in a bit of a bind. Prior to reading all of the posts here (until my eyes bleed), I had poured my slab and set my concrete block to a hearth size of 52" x 64". I will get back to this.

I know the dome circulates heat better and seems to have more usable space. I also understand it takes longer to heat up the vault because of the necessary cladding. I knew most of this from reading the forums before I started with the intention of the barrel vault style, but honestly, the extra time to heat up the vault would be worth it to us as we want to cook a lot of bread and other food in the oven. That, and the easy install of the vault is appealing as I am sure it is to a lot of people. Building that dome correctly looks to be much more difficult than the vault.

However, the more I read here the more I realize in the long run I would probably be happier with the Pompeii oven. The positives outweigh the negatives of the harder build. If all the other people can do it here, it can't be that hard. Right?

Problem is, I already have the hearth slab setup to be 52x64. I am building a house around mine with a roof. With a 36" inside diameter I figure I will need a minimum of 54" wide. 36" + 9" of FB(4.5 each side) + 2" for a 1" thick blanket on each side + 3.5" each side for the metal studs, gives me the 54". I would then just fill in the entire chamber, including the inside of the metal studs, with Perlite. I would have a minimum of 4.5" of insulation all the way around with the combo of blanket and Perlite.

The way I see it, I have a few options. (1) Build the hearth slab out an inch past the cement block on either side and deal with that problem when I go to finish it...(2) Build a smaller dome..or (3) build the barrel vault anyway and put the FB on their flat(2.5") for the bottom and only do 1-1.5" of cladding on the top and sides as a compromise for heat-up time.

Your opinions on this would be greatly appreciated.


dmun 11-09-2008 10:58 AM

Re: To vault or not to vault
A domed oven will bake a couple of loads of bread, or a turkey, or pretty much anything else you want to make in a home setting. It has the additional advantage that you can keep it up to heat all evening long with a few sticks of wood and keep making pizza for the duration of a party. A commercial bakery operation for bread really benefits from the high mass barrel vault oven, where you can turn out load after load of bread. It all depends on what you want to do with your oven. I vote for the dome for home use.

I had a similar problem to you in that I had to keep to a fairly small footprint for my oven. Think about trimming the bricks thin on the side edges, and slipping some refractory board insulation between the edges and side wall. I did this trim trick to make room for a fireplace flue that ended up too close to the dome. No problems so far: it's only the first few courses, as the dome slants inward pretty quickly.

By the way, you can cheat your metal studs for the enclosure, so they skirt the edge of the oven. You don't need the full thickness of the wall at the two points where the oven approaches the edge.

RTflorida 11-09-2008 11:47 AM

Re: To vault or not to vault
I have 3 thoughts
1) Instead of brick halves, use 1/3 bricks - which saves a total of 3 inches. It has been done by others and will definitely work (I don't recall any complaints about heat retention). Also remember, the vast majority of modular ovens are only 2 1/2 inches thick, so I would have no problem going with 3 inches (just means double the cuts)

2) definitely go with dmuns idea of cheating with the metal studs along the sides.

3) double the blanket to 2", you then will not need to worry about having 4+ inches of perlite all the way around, thus allowing you to cheat on the sides with the metal studs.

You can come in under 50" without a problem, and have a solid, well insulated oven.


nissanneill 11-09-2008 01:04 PM

Re: To vault or not to vault
a Pompeii oven need not be 'perfectly circular' nor 'hemispherical' in the dome shape.
You could also stretch out the length of your oven by a few bricks to make it slightly eliptical. It would be no more difficult to build and wold fit your rectangular base. It would also have a slightly greater thermal mass but with all the other advantages of a dome oven.


smuth10 11-09-2008 01:13 PM

Re: To vault or not to vault
Thank you for all the great ideas. I like the idea of trimming the bricks a little where the studs would touch the metal studs. That should get me the extra 1" on each side. I think this would eliminate the need to go to 1\3 bricks. I would like to keep the 4.5" of TM. I found a local place that had Perlite for $9.50 a 4cf bag. I bought 7 bags for under $70 so pretty inexpensive to add the 4+ inches of insulation. A couple more ?'s

How many inches of Perlite\Vermiculite would you say = 1" of the ceramic blanket?

Do you think a thin(1\2") layer of refractory mortar on the outside of the dome would help. Did you guys do this?

Thanks for all of your help. This makes my decision easy. You guys are great!

dmun 11-09-2008 04:29 PM

Re: To vault or not to vault

Do you think a thin(1\2") layer of refractory mortar on the outside of the dome would help. Did you guys do this?
I didn't, mostly because the mortar I used, heatstop50 was silly expensive. If you don't mind the expense, there's no reason not to do it.

70chevelle 11-09-2008 05:11 PM

Re: To vault or not to vault
You could also do as I did and build a "thin" vault. I laid the bricks on the thin end (2.5") and added 3" ceramic insulation. It heats up in about an hour but doesn't retain as long as a conventional vault. I bake bread and pizza's with good results.

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