Hearth Slab, no lime... Newbie Forum Discuss Hearth Slab, no lime... in the Good Background Information forums; If cost is a big factor, just pour 4 inches of the vermiculite cement mixture, that is the same as ...

[DrakeRemoray]

If cost is a big factor, just pour 4 inches of the vermiculite cement mixture, that is the same as 2" of insulating board. That is what I have for mine...

Drake

[KINGRIUS]

Thats a great idea, in fact I still have some perlite left I could use. The problem is HEIGHT. I have poured a front slab that I plan on covering w/roof structure after oven is done. I purposely elevated the oven foundation slab 6" above the front slab to make the oven taller. I am 6' 3.5" (w/shoes) and wanted a taller than average oven to accommodate my height. By the time I add another 4" I'll be on me tippy toes to cook. I think I'll get the 2" insulated board as it is shorter.
However now I am seriously considering taking wise advice from this forum and switching to a Forno Bravo oven, as opposed to a barrel vault oven. My new question is: Will the hearth slab I have poured (58.75" deepX 47" wide) be big enough for a pompeii oven? Looking through the forno bravo manual for stand dimensions for a 36" oven tells me NO, my hearth slab would not be big enough.

[DrakeRemoray]

Well, let's see...36" interior + firebrick (2 x 4") + insulating blanket (2 x 2") gets you to 48 inches wide without any finish...so that would be a problem...

Drake

[KINGRIUS]

Crap. Do you think my barrel vault oven heat up time will be reduced by putting the 2" insulating board on top my hearth slab? And can I just build a smaller barrel vault oven perhaps?

[DrakeRemoray]

Yes, I think you can stick with the barrel vault design sitting directly on insulation and you will be fine! I don't know the Rado book particularly, but a lot of barrel vault ovens have extra mass in the top as well, and really that is not needed for home use either.

But acutally, taking a second look at your picture, you may have room for a 36". Is the slab dimension 47" wide? It looks like you have another 4" or so on either side of your slab, between the slab and the brick wall. Is that true? If that is the case, I think the brick part of your oven could go to the edge of the slab and then the insulation could go in the 4" between the slab and the brick wall. That would allow for a 39" Oven (47" - two oven walls 2 x 4").

Also, a higher oven is not a bad thing. Obviously you don't want to stand on tiptoe, but most professional pizza ovens are way up high, bending over is a pain!

Hope that helps,
Drake

[KINGRIUS]

It's about 2" space on each side between the inside of the brick and the edge of the slab. So that would leave my insulation area to 2". Is 2" enough for the insulation?
Rado's design calls for lots of high-refrac mortar over top of the brick dome, along with steel reinforcing and alumunum foil. All topped off with more high-refrac motar:

[bernerdog]

Try hard to see if you can do the Pompei--it is a treat to build, does not require the mass that the barrel does and ( I hope!!)will fire with a lot more flexibility. I say this with some experience as I built an Alan Scott oven about 14 years ago. Credit is due Alan who was a very early creator and instructor on ovens when no one was writing about them and very few attempted builds. I admit that my Pompei is just underway (I will be insulating in the next two days) and untested but everything about these plans and forum inputs leads me to feel strongly that this little puppy will be great fun and serve me well. I offer no opinion about the sizing problem but several others have expanded their stands or bases to take a wider footprint. Rado`s plans are probably excellent but it is a bread oven much like the Scott ovens and the dome is a much nicer thing to see and build.

[KINGRIUS]

I have decided to build a 32" pompeii oven. This will for 3.5" excess space outside the dome to the edge of my slab and I'll use 3" of the insulating blanket. From what I've read in the forno bravo manual, this should be sufficient enough insulation for my home oven cooking needs. Thanks so much for all your advice. I will need to gather some nickels together for a week or two to buy the 2" insulating board. Then I will start cutting fire bricks and starting the dome! I am sure I will need plenty of your help along the way...

[Neil2]

"The problem is HEIGHT."

Try it. If it feels too high you can always raise your patio.

[KINGRIUS]

Actually the height will end up being right where I had originally planned it to be, around 50" above the front slab. The barrel vault oven design I was going to use had me standing the 4.5" firebricks on their sides as opposed to laying them flat using forno bravo design. I would have lost 2" elevation for that, but since I'm putting down the 2" insulating board I'm within a 1/2" my original height for the cooking surface. But you're right about the front patio, I thought I was going to have to raise it before changing to the pompeii design. But it was a simple matter of laying down some 4" cinderblocks on my front patio slab. But this new plan is easier!