#31  
Old 03-25-2013, 02:59 AM
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Default Re: Before pulling the trigger, in need of criticism

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Originally Posted by giol View Post
It is a calcium-silicate cement with vermiculite as main ingredient, so it should be just a bit a better than vermicrete. It is used as insulating lining for Kiln and in the ceramic industry.
Portland cement is calcium silicate. High temperature cement is calcium aluminate. If your product contains calcium silicate then it is probably very similar to vermicrete which is simply calcium silicate cement and vermiculite, although the brew you have probably contains other ingredients , probably fire clay and a stable aggregate of fired crushed clay and fibres. Calcium silicate is not suitable for the hot face.

I have not seen the photo of the oven you are describing, but many manufacturers (FB included) make entire ovens using castable refractories, but they all use calcium aluminate cements.
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  #32  
Old 03-25-2013, 03:07 AM
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Default Re: Before pulling the trigger, in need of criticism

The product i am refering is calcium aluminate ( like cement fondu) with vermiculite. It does have the same consistency of oatmeal as vermicrete. From what i read this kind of cement (calcium aluminate) has considerably better characteristcs for high temp applications then portland cement.
The engineer that sold me this warned me that i have to get the inside of the dome to 500 C and hold it there or above for an hour at the end of curing. If this is done this thing will become more solid and will achieve it's full potential, otherwise it will stay concrete.
David i saw your build and i am wondering how is your casted arch holding. I casted a "pizza hacker" type of cover for my broilking bbq and allthough it is very strong and i have no cracks, it is very easy to scratch it with sharp tools. I am wondering if that would be a problem with pizza shovel.

Last edited by giol; 03-25-2013 at 03:13 AM.
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  #33  
Old 03-25-2013, 04:15 AM
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Default Re: Before pulling the trigger, in need of criticism

With your planned 5" thick walls, that's more than enough thermal mass. The insulation surrounding it does not need to be an expensive calcium aluminate based product. The temperature on the outside of your inner brick walls does not warrant it IMO and is a waste of money. Calcium silicate cement (Portland) is sufficient.There is no way you will get that stuff up to 573 C (the temperature required to "fire" the castable, if you place it outside your bricks. What happens to the insulation over the dome is immaterial once it's coverd with render or stucco. I'm assuming you are planning an igloo style here. If you are doing a dog house then you are better off filling it with loose insulation.

Last edited by david s; 03-25-2013 at 04:43 AM. Reason: Typos
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  #34  
Old 03-25-2013, 04:31 AM
Peasant
 
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Default Re: Before pulling the trigger, in need of criticism

I am planning on iglooish shape. Two semircles connected with a 5 inch "extension " because I have limited space in width and I want to achieve the space of a 34 inch oven to fit my needs.
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  #35  
Old 03-25-2013, 04:47 AM
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Default Re: Before pulling the trigger, in need of criticism

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Originally Posted by giol View Post
I am planning on iglooish shape. Two semircles connected with a 5 inch "extension " because I have limited space in width and I want to achieve the space of a 34 inch oven to fit my needs.
I'm now confused because two semi circles connected sounds more like a barrel oven, rather than a dome which is hemispherical.No matter, the insulation procedure is basically the same.
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  #36  
Old 03-25-2013, 05:00 AM
Peasant
 
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Default Re: Before pulling the trigger, in need of criticism

it will be more of a slight elipse with 100 cm depth and 76 Cm width. Otherwise I will have a barely 30 inch oven and I have 3 kids and a lot of hungry friends. I will compromise some efficiency for the extra space. I think that it will still be closer to a dome than to a barrel. What do you think?
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  #37  
Old 03-25-2013, 05:10 AM
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Default Re: Before pulling the trigger, in need of criticism

Ok, that makes it clear. I have seen ovens of this configuration and they fire perfectly well. The mouth of the oven at the end is better than having it sideways and in the middle. These ovens don't fire so well from all reports and are harder to manage because it's harder to get to the sides. The difficulty is that it will be harder to build an ellipse in brick. Perhaps the best approach would be to build over a sand hump and remove the sand after forming the brick walls, although getting all that sand on to your balcony may be difficult.

Last edited by david s; 03-25-2013 at 05:12 AM.
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  #38  
Old 03-25-2013, 05:18 AM
Peasant
 
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Default Re: Before pulling the trigger, in need of criticism

You are right. I am thinking of marking two pivot points 5 inches apart for my IT and using this. I am afraid that with a sandform I won't have perfect curves "so to speak " and my wife, who is only letting me do this because she wants to tile it with mosaic, will be pissed of.
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  #39  
Old 03-28-2013, 01:44 PM
Peasant
 
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Default Firebrick pieces between courses?

I was wondering if i could use some leftover firebrick splits and cuts between the courses to support the right angle and mortar them inside?
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  #40  
Old 03-28-2013, 01:55 PM
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Default Re: Before pulling the trigger, in need of criticism

Yes, builders often use this technique, or some wooden wedges that you can remove as you go. I cast most of my domes rather than making thousands of brick cuts, so am not as experienced as many others in this build method, but it is possible to make the dome oven using half bricks cut with a brick bolster and make the thing without any angled cuts at all.You just need more mortar to fill the spaces. Your wife will not enjoy brick cutting and all the associated dust it creates on your verandah.
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