Newbie Mistake, Will I be Ok?

[Pizza-n-Jazz]

I have been working like crazy for 3 weeks and have come to the dome. After reading some stories about losing heat and other problems I am a little confused and worried.
I poured a 3 1/2 inch slab on the blocks and then 3 1/2 inch slab of the portland/vermiculite mix and added 18 fire brick splits under the dome floor area. Do I still need ceramic board at this point?

[phippsj]

Re: Newbie Mistake, Will I be Ok?

From everything I have read you can use the FB board to replace the vermiculite, but you don't have to. I have seen in other builds where they used 4.5" or even more on the vermiculite slab. I did a 4" vermiculite with no FB board.

[Tscarborough]

Re: Newbie Mistake, Will I be Ok?

Normally the floor is made with full fire bricks, but the splits will work, they just won't hold as much heat. You would not put insulation on top of them, then more firebrick on top of that, though.

[Pizza-n-Jazz]

Re: Newbie Mistake, Will I be Ok?

Thanks for the reply, I came up short on the vermiculite by 10% and so I added the split bricks at the last second to take up some space. I think on page 29 of the FB oven plans it said this would help hold some heat. It was 10:30PM when this happen so going back to the store was not possible.
The portland/vermiculite mix is pushing 1 1/2 to 5 ratio (to make the pour)so I was a little worried when I read some posts about heat loss or not heating at all. I guess I should start working in the AM but being a musician I get my energy high at night time.
The one good thing is that I live around 400 pecan trees and wood is not a problem. Thanks again for the help.

[DrakeRemoray]

Re: Newbie Mistake, Will I be Ok?

So you will have an extra thick floor on top of slightly thin (by 1/2 inch) insulation? It is going to have to be your call, but you really don't need extra mass in the floor. It will just make heat up take longer and really there is plenty of stored heat in the regular design without adding additional mass to the floor. This is somthing you can only fix now, so I would consider pulling up the floor and adding some additional insulating board (and this really mostly to get the floor up to the height you want). 3.5 inches would probably be OK on the insulation, but the extra mass could be a killer IMO.

[Neil2]

Re: Newbie Mistake, Will I be Ok?

Or put on another 2 inches of vermicrete.

[Pizza-n-Jazz]

Re: Newbie Mistake, Will I be Ok?

Sounds like I need to cut out the brick and insert a ceramic board. Glad the dome was not started. A million thanks and if I ever win the lotto you guys are set!!

[DrakeRemoray]

Re: Newbie Mistake, Will I be Ok?

Did you set the splits down in the vermiculite? You may be able to just dig them out and pour another layer...
Also, I cannot view that picture...

[Pizza-n-Jazz]

Re: Newbie Mistake, Will I be Ok?

DrakeRemoray, I put the picture in Photo Gallery under Hearth and Stand "David's Mistake". I think that taking out the brick and going with port/verm or ceramic will give me the 3 1/2 that I need. I have some 1200F pipe insulation but its fiberglass type, is this some that might work? Thanks

[azpizzanut]

Re: Newbie Mistake, Will I be Ok?

Hello P n J,

I looked at your photo. Here's what I would do. Dig out the firebrick splits and pour the void level with 1:5 insulation. If you decide to put down insulation board, then place it so it will fit the oven footprint. Lay the full hearth bricks on top of the board.

Cheers,

[DrakeRemoray]

Re: Newbie Mistake, Will I be Ok?

I found the picture:


I think that I would dig it out. I would not use that fiberglass insulation, it will probably compress and lose it's value. You will be happy in the end for fixing this up front....

[lwalper]

Re: Newbie Mistake, Will I be Ok?

Wow! What a great start!! So, you've got 3?" of vermicrete?—and you're going to add more of "something" to bring your hearth height up to the desired level? I may not be understanding exactly what you're trying to accomplish.

I wouldn't tear out anything. Sure, you could rip out and add more insulation, but in the overall scheme of things I don't think you'll see much difference in the actual performance of the oven. OK, your thermal loss through the bottom may be a little higher than "Joe's next door," but if your primary use for the oven will be to cook pizza that should not really be an issue.

From the surface of my hearth to the bottom I've got 15 inches of brick, concrete, vermicrete, and more concrete—and after a few hours of firing I still have 130? temps through all that—but the hearth remains 425? for 48 hours after the fire is removed.

I'd just continue to build on top of what you've got. If you need to add more "something" to get additional height for the finished hearth, since you've already got your insulation layer add more concrete, or turn the hearth bricks on their side instead of laying them flat. You can always just continue with more vermicrete on top of what you already have. You'll be adding a little more mass to the hearth than you had intended, but hey, put a fire in there and it will get hot just like the guy next door. I just hate ripping stuff out - especially concrete. Go with it - it'll work just fine. It may take the hearth 30 minutes longer to come up to baking temps, but with the additional mass you can bake more pizza - mmmmm good.

If you decide to add more vermicrete you might go with a lower density mix - say 10:1. I used 9:1 and wish I had gone to the 10:1 (or even a bit higher). It will be softer, but after curing for a couple of days still stiff enough to support the hearth bricks and provide better insulation.

[Pizza-n-Jazz]

Re: Newbie Mistake, Will I be Ok?

lwalper, man, 15 inches and still gets 130F to the other side. Well I did take out the brick today and (get this) the place I went give me the ceramic board! 12 sqare feet 2 1/2 inches thick so the problem is taken care of.
I did buy my ceramic blanket (50 sq.ft.) as well and he even gave me 25 pounds of ceramic fire clay.
I don't know if I should post this in another section but this supply house also had high duty fire bricks that were 9 pounds each. I told him that the brick would take to long to heat. Is this right? If they would work he only wanted 2 dollars each. He also had some white honey comb brick that were light weight and tappered that had a 2300F duty temp. I think they hold heat in and not take in heat but they to were only 2 dollars each as well. Should I stick with light fire bricks or try out the high duty bricks? Thanks for all of the help so far.

[fxpose]

Re: Newbie Mistake, Will I be Ok?

Read this before you buy bricks: Brick Oven Design | Choose the Right Brick Oven Brick

[DrakeRemoray]

Re: Newbie Mistake, Will I be Ok?

I agree that it is a pain to pull out and more of a pain to mix perlcrete again. But the hearth of the pompeii is already twice as thick as some of the ovens they sell at Fornobravo, and this would add 50% more thickness. It would also be difficult to remedy the problem after the dome was built (if it turned out to be a problem at all)...

If you want extra mass in the oven, I think it is better to add it to the dome. I added an inch of mass to my dome, and I have killed myself trying to use it all the heat in the oven after a long pizza burn...

http://www.fornobravo.com/forum/f11/32-lbs-bread-5456.html