Forno Bravo Forum: The Wood-Fired Oven Community

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-   -   Getting started questions (http://www.fornobravo.com/forum/f6/getting-started-questions-414.html)

mnreeder 02-17-2006 06:22 AM

Getting started questions
 
Okay, I am starting to get spring fever and now have congressional approval for my pompei oven (my wife).
I found some really nice blocks with a rough finish face on them already. I think that will give me an easy and nice base look. I tracked down my fire-bricks for about $1 each.
Now just a few questions and opinions if you please.
I believe that I will go with just concrete, rebar, and then vermiculete for my hearth (bricks right on insulating layer).
My main question is about dome thickness/insulation. I read all the threads, but I didn't know if there was a consensus. If you builders were doing another oven, mainly looking for quick-fire times and not so worried about long retention times. What would you do for thickness and insulation order? I will not enclose the oven. I will go with the standard igloo (with stucco finish).

Thanks,
Mike

DavidK 02-17-2006 07:17 AM

Thinner is better!
 
For pizza crust and refractory layers...

Mike, I just finished my stucco work on a 36" The pics are under the pompeii oven constuction thread. My mortar layer is no more than 1" and probably closer to 1/2" in most places. On the other hand, my insulation layer is a full 6" thick. I was too impatient (and cheap) to get the insulation blanket although I could have trimed the insulation layer back to 4" with it.

After a long firing, I cannot feel any heat through the insulation so it must be pretty efficient at retaining heat. The lower part of the chimney on the other hand gets outright blazing! As for heatup, I can get to cooking temp in under an hour (40-45min) so I'm pleased with it's heating efficiency. As for retention, I don't have a great sense because I just haven't used it enough, but I do know that the next morning, the oven is usually in the 200+ degree range.

That's a long-winded way of saying, go light on the heat sink and heavy on the insulation! I wouldn't change a thing!

Good luck!

mnreeder 02-17-2006 07:59 AM

David,

It looks like you have built almost exactly what I am shooting for. I will go with the 36" also.
If you did it again, would you go with the blanket or stick with the 6" of perlcrete?
Also, have you finished your stucco yet? If so, what was your layer order on top of the perlcrete. If not, what is your plan. Can you stucco right on the perlcrete. Seems that the surface would be rough enough for sticking, or are you going to used chicken wire.
BTW, great looking oven. However, we just got another foot of snow, so I will have to just collect supplies for now. One last question. Do you have a total price estimate on just the oven part of your project?

Thanks again,
Mike

DavidK 02-17-2006 10:42 AM

Mike, I'd probably still go with the 6" and skip the blanket. The cost of perlite and cement is minimal and once you get going, 6" is as easy as 4". There's just that much more to mix. I did all my mixing, except the foundation which I had pumped, in a 6cf wheelbarrow. Renting a mixer would have really speeded things up, but it wasn't that much trouble, it's good exercise, and I didn't have to plan, rent and return a mixer. It took three hours or so to do the insulation layer, beginning to end.

Stucco is done. I'll get pics up next week. Two layers- scratch and finish. Used expanded diamond lathe over the perlcrete for better adhesion and because my building dept. required it... I used 11/2" galv. ring roofing nails to attach it to the perlcrete and tin snips to section it and get a close fit.

As for a cost estimate, I have no idea--$1,000 or so. I could tell you the cost of the individual pieces and you could go from there. There's a Material List for 36" Oven thread in the Pompeii Oven Construction folder. I'll go add the prices where I can. Naturally they're only accurate here in S. Fla., but it should help.

And thanks for the compliment. I couldn't have done it without the help from so many people here. Paul, Marcel, Tarik, Robert & James to name just a few... Feel free to email directly or pm me if you have more questions or run into any snags.

mnreeder 02-20-2006 02:02 PM

Thanks David, brick saw on sale
 
I appreciate your thoughts on the blanket. That seems so true about adding 2 more inches.

Is the diamond lathe you used, like a sheet metal with little nubs popped up for roughness? That sounds like a bugger to get it to your igloo shape. Isn't it a fairly solid piece of metal? Maybe I'm thinking of the wrong thing.

Don't worry about more specifics on the money side. I was guessing around $1000ish. Just wanted to make sure I wasn't way, way off.

Thanks again for the help and replies.
You are so right about the great help in this forum.
I literally read every post in here (except recipes), before even asking any questions.

By the way, I noticed several other people getting spring fever and starting or thinking of starting ovens right now. I thought I would mention that Harbor Freight does have their 10" tile/brick saw on sale right now. It is the pump style not the pan/splash style. I think it was regularly $399, down to $199. I think it ends on feb 27th, but not positive. I'm not a huge fan of some of their tools, but I've heard several other people have bought them.

Thanks,
Mike

mnreeder 02-24-2006 05:52 AM

David if you are still out there (or someone else who may have experience with this). I am wondering if you used foil or any other slip plane in your insulation? Or did you just do your 6" of perlcrete directly onto your brick/brick mortar.

If you didn't, do you think you should? Anyone else think that this should be done when not using a blanket?

Thanks

CanuckJim 02-24-2006 06:50 AM

Foil
 
As David Wing and Alan Scott suggest, I certainly did use foil over the bricks, before the reinforcing mesh went on. They state that this prevents hot spots in the dome and walls, and it seems to. The only question is how many layers. Alan Scott's own plans specify one layer of HD foil. At one point in the Bread Builders, the text specifies one layer, but in another it specifies three layers. I used three, but, then again, I overbuild just about everything.

Jim

james 02-24-2006 10:33 AM

No need for foil
 
Mike,

This is one area where the Pompeii oven and the Scott oven are different in design.

The Scott oven has a brick oven chamber, encased with an addition 5" of concrete. Both of these layers are thermal, and make up the mass of the oven. That's where the oven's 9"+ of thermal mass comes from. Because both the brick and concrete are thermal, but move differently during thermal expansion and contraction, you need a slipe plane between them to decrease the chance of cracking and wear.

The Pompeii oven has a single thermal layer -- the brick dome held together with fire mortar. That's it. There isn't a second thermal layer, so no need for foil.

The insulating layers (some combination of Insulfrax, loose vermiculite or perlite, or castable vermiculite or perlite) stop heat, and keep it inside the oven. You don't need a slip plane between the thermal and insulating layers, even if you don't use a blanket.

I think this is a really good question, because it highlights an interesting aspect of oven design.
James


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