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Old 10-20-2013, 09:45 AM
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Default planning questions

i'm planning a build in CA. probably a 36". i've worked a little w/ stone and metal before. i've been lurking and reading, but i still have a couple details i'm unsure of, if you don't mind.

i live near enough FB HQ that i can drive there and pick up supplies to save shipping. i'm planning to get the mortar, insulation board and blanket, chimney, from them and source the bricks locally.

is the hearth insulation set on a skim coat of mortar, or sand, or caulked down in some way, or is it just pressed down from the weight of the bricks? seems like it could move over a month+ build if not anchored.

i see folks adding a bottle/can to the top of the vermiculite insulation, presumably as some kind of vent. what are the details on this? i don't really understand it.

i see some folks separated the chimney from the dome. i don't really see why this is necessary. shouldn't both heat up, and both have insulation? the dome will heat cycle far more than the chimney, so why so much concern?

if i stucco over the igloo, i'm assuming i still want the entire stucco igloo to "float" above the hearth for expansion. the FB instructions talk about rebar into the hearth and a mesh on that for stucco, but that doesn't seem right to me.

thanks for any help you can provide a newbie.

-SM-
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Old 10-20-2013, 10:39 AM
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Default Re: planning questions

Quote:
Originally Posted by tikidollracer View Post

is the hearth insulation set on a skim coat of mortar, or sand, or caulked down in some way, or is it just pressed down from the weight of the bricks? seems like it could move over a month+ build if not anchored.
Just place the board on the hearth - it won't go anywhere

Quote:
i see folks adding a bottle/can to the top of the vermiculite insulation, presumably as some kind of vent. what are the details on this? i don't really understand it.
Not sure I have seen this, your assumptions of a vent is probably correct. If you cure slowly it would not be needed. If you can afford it, I would purchase the blanket then it's a non issue.

Quote:
i see some folks separated the chimney from the dome. i don't really see why this is necessary. shouldn't both heat up, and both have insulation? the dome will heat cycle far more than the chimney, so why so much concern?
Some have done this to act as a heat break. I personally did not do this and have zero regrets.

Quote:
if i stucco over the igloo, i'm assuming i still want the entire stucco igloo to "float" above the hearth for expansion. the FB instructions talk about rebar into the hearth and a mesh on that for stucco, but that doesn't seem right to me.
This was my approach. I bent the rebar into a radius and dropped the ends into holes I drilled in the hearth
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Old 10-20-2013, 02:55 PM
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Default Re: planning questions

"if i stucco over the igloo, i'm assuming i still want the entire stucco igloo to "float" above the hearth for expansion. the FB instructions talk about rebar into the hearth and a mesh on that for stucco, but that doesn't seem right to me."

I went down the standard road with the igloo and put ceramic fibre insulation over the brick dome, wire mesh over that, vermicrete and then rendered over the top of that. The CF allows the vermicrete and render to 'float'. I have been using mine for some time and the dome is still like the day I finished it.

Good luck with your build. There are some good ones to emulate on here. Mine is functional and I am happy with it. The pics in the link below might help you clarify some of the issues you are contemplating.
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Old 10-20-2013, 04:01 PM
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Default Re: planning questions

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I went down the standard road with the igloo and put ceramic fibre insulation over the brick dome, wire mesh over that, vermicrete and then rendered over the top of that.
Agreed - I took the step of adding the rebar. It just seemed that I would be able to control the shape a little better
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Old 10-20-2013, 04:43 PM
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Default Re: planning questions

thanks, just to be clear i plan on doing the blanket and a vermiculite layer over the blanket. i'm after heavy insulation for multiple day cooking. i haven't decided on final form. either stucco igloo or square form filled w/ vermiculite.

-SM-
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Old 10-20-2013, 05:53 PM
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Default Re: planning questions

Quote:
Originally Posted by tikidollracer View Post
thanks, just to be clear i plan on doing the blanket and a vermiculite layer over the blanket. i'm after heavy insulation for multiple day cooking. i haven't decided on final form. either stucco igloo or square form filled w/ vermiculite.

-SM-
Thats what is in the picture. I have a minimum of three inches of blanket under 2-3 inches of vermiculite ( if I remember the numbers right)
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Old 10-20-2013, 07:02 PM
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Default Re: planning questions

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Originally Posted by tikidollracer View Post

............i see folks adding a bottle/can to the top of the vermiculite insulation, presumably as some kind of vent. what are the details on this? i don't really understand it..............


-SM-
The beer bottle/can is kind of a joke. But, it does serve the purpose of forming a hole in the vcrete to allow trapped gasses (steam between the firebrick and vcrete) to escape at the apex of the dome on igloo styles. The hole adds another problem, though. It must be capped with a venting rain proof cover.

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Old 10-20-2013, 08:14 PM
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Default Re: planning questions

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forming a hole in the vcrete to allow trapped gasses (steam between the firebrick and vcrete) to escape at the apex of the dome on igloo styles.
you see steam coming out your vent cap when you heat the oven? photo?

how is water getting trapped in there to form steam? all the gases in the oven should be convected out the chimney. the water in the mortar should have reacted. the outside shell should be impermeable to H2O.
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Old 10-20-2013, 09:34 PM
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Default Re: planning questions

Gudday
Sounds good in theory.... But in the real world high humidity will be drawn into the bricks naturally. The Hearth has brick / tile has with have cracks that capillary action will take the water straight to your under insulation. Chimneys brick, ceramic,or metal expand and contract and cause cracks.
A damp oven is going to happen sometime you just fire it till it dries and cook in it as you do . The vent helps when it does happen.
Regards dave
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Old 10-20-2013, 09:51 PM
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Default Re: planning questions

It is about both getting rid of any moisture that is left in the mortar/firebricks/stucco from the build. Some people are inclined to moisten their bricks to different degrees when building the dome. (best we don't start that conversation again). It also provides a vent for moisture that finds its way into the oven after it is completed and cured.

I used an irrigation fitting with a threaded cap and then put a small chinamans hat over that. I was going to just use the little cowl but it was pointed out that the aluminium would react with the mortar over time so it now just sits over the PVC threaded cap.

How you form the cavity through the vcrete is up to you.

I might be considered to be one of those things that it is better to have and not need rather than need it and not have it.

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