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Old 11-01-2009, 05:50 PM
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Default Concrete vs refractory cement for mass

Hi,
I want to add the optional extra mass over the vermiculite insulating slab. Do I really need to use refractory cement or can I use reinforced concrete instead? I like the idea of spreading the load on the vermiculite considering that I will have a masonry chimney partially supported by the oven/vermiculite slab. I am thinking concrete because I assume it would be stronger and it is certainly cheaper.
Thanks,
Dave
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Old 11-01-2009, 06:16 PM
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Default Re: Concrete vs refractory cement for mass

You can use use pretty much anything. The distributed loads are minimal.
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Old 11-01-2009, 06:27 PM
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Default Re: Concrete vs refractory cement for mass

Dave,
I used Quikrete SBC, surface bonding cement, Love this stuff,, very easy to work with and adds structural strength as well.. you can also add color and Acrylic Fortifier for waterproofing.. I think its about $ 19 a bag at lowes, I used 2 bags to put 2 coats on my 42 inch dome.. And no, you absolutely do not need refractory cement....

Hope this helps
Mark
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Old 11-01-2009, 07:43 PM
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Default Re: Concrete vs refractory cement for mass

Quote:
I want to add the optional extra mass over the vermiculite insulating slab.
I may be interpreting this sentence differently (read: wrong) but I think the question is about adding mass under the oven floor. This really isn't needed. If you do go this route, do a forum search for "island hearth" for the brief time when it was thought necessary to add to the oven floor mass.

If it's under the floor, but inside the insulation envelope, you may want something that's heatproof. Some builders have laid their floor bricks on edge to build up mass.
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Old 11-01-2009, 07:57 PM
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Default Re: Concrete vs refractory cement for mass

Why do you want to add the additional mass? Unless you are going to mass produce bread commercially, you won't need it. For a backyard oven to be used for home, family and friends, you won't need the mass. And it may frustrate you because it takes longer to heat up and uses more wood.
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Old 11-01-2009, 08:24 PM
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Default Re: Concrete vs refractory cement for mass

Quote:
I may be interpreting this sentence differently (read: wrong) but I think the question is about adding mass under the oven floor.
in that case disregard my answer as I thought you were talking about over the dome...

Thanks david for pointing that out...

Cheers
Mark
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Old 11-01-2009, 10:05 PM
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Default Re: Concrete vs refractory cement for mass

Thanks for the input. I was thinking about under the oven floor but over the dome was a question in the back of my mind also. I just searched Hearth island and found some good reading. My thought is that I can always add more wood to the oven but I can't add mass later. My wife has kicked around the idea of making a lot of bread on the weekend and taking it to the local farmers market. With this in mind (although it will likely never happen) I was thinking about the extra 1.5 inches below and around the oven. It sounds like this is discouraged based on experience.
Dave
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Old 11-01-2009, 11:35 PM
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Default Re: Concrete vs refractory cement for mass

Given that the extra mass is out of sight and its strength is not an issue I think you could use ordinary concrete provided that you reduce the portland cement content and replace that taken out with lime. The portland cement gives up at around 300 C, but the lime is ok.
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Old 11-02-2009, 02:57 AM
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Default Re: Concrete vs refractory cement for mass

Quote:
My wife has kicked around the idea of making a lot of bread on the weekend and taking it to the local farmers market. With this in mind (although it will likely never happen)
Im guessing your wife is not a memeber of the forum.... If you really want the mass, Like david said just turn the bricks on their side and you will have almost double..
Cheers
Mark
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Old 11-02-2009, 06:27 AM
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Default Re: Concrete vs refractory cement for mass

I agree with Mark. When the oven is fully saturated, the bottom of the floor will be hot enough to cause problems with portland. I considered putting the floor bricks on their side thinking we might cook a lot of bread, but the forum convinced me I won't make that much bread. But it would look really cool.
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