#1  
Old 05-30-2006, 09:17 PM
Laborer
 
Join Date: May 2006
Location: Ravensdale, WA USA
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Default Hearth Questions

Hello from near Seattle. I've been working slowly toward my oven since last fall and with the weather getting better I'm actually able to work outside. I poured the slab last fall and had the concrete blocks strategically stacked until a month ago. Since then I've arranged the blocks in the proper manner and have poured the concrete into the holes in the blocks that were doweled together to the slab. Now I'm getting ready to try the hearth and have a couple of questions. I'm pretty sure from what I've read that some of the oven builders ahead of me can answer these questions.

1. In the new hearth configuration would there be any reinforcement in the insulating portion? I'm thinking not.

2. Is the insulating part of the hearth (top 4 inches or so) structurally sound enough to support the dome? I realize the dome's weight would be at the outside of its circle. In some earlier postings I noticed a couple of builders that isolated the part of the slab outside the dome area by using a metal and in one case a wooden separator for more standard concrete at the outer edge. I have seen a recent picture that shows anchor bolts extending through the insulating pour into the structural concrete. This sounds like a good idea.

3. Is the insulating layer simply a portland cement and vermiculite mix?

Thanks for your help. We're reaching critical mass out here in the woods.

Mike
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  #2  
Old 05-30-2006, 10:06 PM
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Location: Pebble Beach, CA
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Welcome aboard Mike,

Great questions.

1. The insulating concrete does not have rebar. It wouldn't help, and could even be a negative if the metal ever got hot. The goal of that layer is to stop the heat, keep it from migrating south, and keep it inside the oven and in the cooking floor.

2. The vermiculite layer only needs to support the oven from a compression point of view. There is a posting in the Forno Bravo forum (somewhere) where Jim (Col. Corn) calculated the compression strength of vermiculite concrete and found that a brick oven is only a fraction of what vermiculite can support -- vermiculite concrete is also used underneath swimming pools, which are a lot heavier than a brick oven.

The structural support for the oven -- what keeps it from sagging or falling in, is the 3.5" concrete layer under the vermiculite layer, and that has 1/2" rebar on 12" centers.

3. Yep. Pure portland cement and vermiculite. It's a castable insulator when you mix it that way. 5-6 parts vermiculite and 1 part portland. Blend the vermiculite and portland, add water and mix by hand. It feels like oatmeal at that point, but sets really well.

Enjoy your project -- and your oven. Hey, after you are done, you get to use Robert's' flame thrower.
James
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Old 05-31-2006, 07:03 AM
DrakeRemoray's Avatar
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Location: Littleton, CO
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Quote:
Originally Posted by El Puaco
I have seen a recent picture that shows anchor bolts extending through the insulating pour into the structural concrete. This sounds like a good idea.
I put the anchor bolts in the structural concrete. This is strictly to give me a way to attach the outside walls of my enclosure without having to drill through the insulating layer and into the structural layer.

Drake
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Old 05-31-2006, 07:31 AM
Laborer
 
Join Date: May 2006
Location: Ravensdale, WA USA
Posts: 92
Default Oh yeah, just one more thing....

Thanks guys.

Another question regarding the vermiculite hearth business. Will it finish smooth enough so that the fire brick will lay out nice and even? I'm getting pretty wound up about this thing.

Thanks again,

Mike
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Old 05-31-2006, 08:23 AM
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It will not be smooth, but it should be level. Since you will then spread a thin layer of Fireclay, Sand and Water on top of that, you will be able to get it pretty level. Other have pointed out that firebricks themselves are not that uniform, so some will sit flatter than others.

Some have used an angle grinder to flatten out the hearth, but the ground bricks are not as smooth as the finished side of a brick...

Hope that helps.

Drake
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  #6  
Old 05-31-2006, 09:10 AM
Laborer
 
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Location: Ravensdale, WA USA
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Default Hearth

Drake

Thanks again for your help. I think I've got now, at least for this next step. Please bring me up to speed on your progress.

Mike
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  #7  
Old 11-24-2006, 03:09 PM
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Default blowing up

hello, im a newbie here, i've been searching for sites that would help me repair my brick oven. Actually it's our second Italian Pizza brick oven. The curing of the first one went well. But the second one... well while firing it for the first time, the cement from the flooring of the oven exploded. i guess the temperature went up so fast for a short time. since we didnt build the oven ourselves, i was wondering if anyone from this forum could help me or give me advice on how to repair the flooring that just exploded. thanks !
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Old 11-24-2006, 03:16 PM
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Yikes,
You came to the right place. Can you send any photos?

Can I ask a couple of questions?

Do you know how you constructed the hearth, and what it is made of?
Is the floor brick?
Does the dome sit on the floor, or on the hearth, around the floor.
When you say it exploded, what exactly happened?
How many fires have you had, and how hot was the oven?

Let us know.
James
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Old 11-24-2006, 04:00 PM
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I'll try to get photos of the oven when I go back later, but I believe the the hearth was made from refractory cement. I am not totally familiar with refractory cement but based from the broken pieces it seems that it was mixed with some sort of gravel.

I have to fix this oven quick, any advice will be most appreciated.
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  #10  
Old 11-24-2006, 04:21 PM
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Join Date: Nov 2006
Posts: 6
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Quote:
Originally Posted by james View Post
Yikes,
You came to the right place. Can you send any photos?

Can I ask a couple of questions?

Do you know how you constructed the hearth, and what it is made of?
Is the floor brick?
Does the dome sit on the floor, or on the hearth, around the floor.
When you say it exploded, what exactly happened?
How many fires have you had, and how hot was the oven?

Let us know.
James
Will try to get photos when I go back and post it.

I believe the whole oven was made from pieces of refractory cement. The floor is divided into 5 sections and is separate from the dome;4 quarter circles, and a diamond center.
It was the first time we had the oven fired up. During the burn, we heard several loud explosion but disregarded it to be just wood crackling, but after an extremely loud explosion, we saw the diamond center piece of the flooring reduced to rubble. We only reached a max temp 250 degrees.
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