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  #11  
Old 08-21-2010, 12:18 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

"I installed about 3/4 ton of railroad ties as a 2' tall by 30' long retaining wal"

I'm not sure of the details, but I would suggest that your oven footings and walls be completely independent of the retaining wall. (Had planned to sit the oven foundation on top of the fill supported by the retaining wall ?)
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  #12  
Old 08-21-2010, 01:38 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

Thanks! That's exactly the info I needed! As for the 4 inch vs. 2 inch vermiculite layer issue, is there some prior experience with this, or are you saying to play it safe with more rather than less? My curiosity is because one of the Newbies in this strand above pointed out that the firebricks don't get fully hot on the opposite side of the fire, so why so much insulation? (As you can see, I like to understand what I'm doing rather than just "do the usual!")
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Old 08-21-2010, 02:18 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

Quote:
2 inch layer of Vermiculite/concrete
I agree with Tscarborough: two inches is too little by half. If your design limits you to that thin an insulation layer, you need to use a refractory insulation board, either mineral fiber, or cal-sil.
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  #14  
Old 08-21-2010, 02:42 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

Because perlcrete costs about 4 bucks a cubic foot one time and good wood costs a buck a cubic foot every time you use the oven.
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Old 08-23-2010, 04:31 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

Quote:
Originally Posted by Neil2 View Post
"I installed about 3/4 ton of railroad ties as a 2' tall by 30' long retaining wal"

I'm not sure of the details, but I would suggest that your oven footings and walls be completely independent of the retaining wall. (Had planned to sit the oven foundation on top of the fill supported by the retaining wall ?)
My yard is on a hill.

There will be a couple of retaining walls. The one I installed is on the downhill side near my garage. It's completely separate from the patio area, there will be about 6 feet of garden bounded by the downhill side of the patio and the uphill side of the railroad tie wall. It is structurally isolated from the patio/oven/etc. It was necessary because soil, debris & such was backing up against the garage and rotting the exterior. It's to the right in my photo on post #7.

The uphill wall is planned to include the oven footing, and will run along the lefthand side of the pit seen in the photo on post #7. The wall and oven footing will be on the poured patio slab, with an extra 12" w/rebar below the CMU. The idea is that the oven is in the corner, into the side of the hill (the soil should be about 18" - 24" up on the backside of the oven).

So the base of the oven will not be on top of the fill above the wall, but on the same slab that the wall rests on.

Hope that helps. And if it doesn't make sense, let me know - I'll hopefully only build one patio with a WFO in my life. I want to do it right.


Edit - I've added a little sketch to the photo which hopefully makes some sense.
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Last edited by Cheesehead; 08-23-2010 at 04:41 PM. Reason: Added pic
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Old 08-23-2010, 04:54 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

Quote:
Originally Posted by luca View Post
My curiosity is because one of the Newbies in this strand above pointed out that the firebricks don't get fully hot on the opposite side of the fire, so why so much insulation? (As you can see, I like to understand what I'm doing rather than just "do the usual!")
As the newbie in question I'd like to say that I'm planning on going with the full amt of insulation if not more, both underneath and on top. I'm also trying to understand what I'm doing and how the design works... in particular, how much "thermal mass" (heat capacity of the oven relative to the rate of heat flow outwards) is required.
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  #17  
Old 08-23-2010, 06:06 PM
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Default Re: Newbie dome question - 2.5" thick instead of 4.5?

"So the base of the oven will not be on top of the fill above the wall, but on the same slab that the wall rests on."

Sounds OK. Fills will settle somewhat more than native ground Differential settlement is the concern.
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