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cbhlaw 07-21-2009 12:11 PM

AS Oven Question
I am currently in the process of building an AS barrel type oven. I have modified the plans slightly and would like some advice. The inside dimensions are approximately 32 inches wide by 36 inches deep and 16 inhes high at the peak of the arch. I constructed the hearth slab with 4 inches of concrete, followed by 2 inches of 1900 degree insulation, covered with approximately 1 inch of 1200 degree refractory material, followed by fire brick layed 2-1/2 inches thick. My walls are firebrick layed 9 inches high by 4-1/2 inches thick. The dome is also layed 4-1/2 inches thick. My concern is as follows. I only have approximately 4 inches of space from the outside of my barrel walls to the inside of the final cladding (regular brick). I have read many posts that require the walls to be buttressed to support the dome when heat is applied. By following the AS plans this would require the dome to be covered with 3 more inches of concrete, thus adding to the thermal mass. I don't think I need this thermal mass and if I do so only have 1 inch of insulation space on the two side walls. Would a 4 inch layer of 5:1 vermiculite/portland be sufficient to support the side walls? Any advice would be appreciated.

Neil2 07-21-2009 03:06 PM

Re: AS Oven Question
"Would a 4 inch layer of 5:1 vermiculite/portland be sufficient to support the side walls? "

As I understand, this would then be supported by your outside brick walls ? If so then you should end up with sufficient buttressing. 5:1 vermiculete has a surprising compressive strength. I would be tempted to back this off to about 8:1 for a better insulation value. For that size of arch, you would probably only need the vermiculite for about 6-8 inches up and go with either loose vermiculite or a 12:1 mix above that

cbhlaw 07-21-2009 08:12 PM

Re: AS Oven Question
Yes, the outside walls would add to the buttressing. However, since they will also support the brick arch cladding I assume that I may need to make this outer arch more of a semi-circle to avoid the same circumstance? My intention was to shape the vermiculite mix with a form to act as the "back up" for the arched brick cladding. Would you suggest following your original idea only eliminating the loose vermiculite? Another possibility that I thought of was to install a 3 inch reinforced concrete wall around the sides of the dome (dowel into the slab) and add 1 inch of rigid 1200 degree insulation (6 to 8 inches up), with the top of the dome following your 8:1 mix and keeping the outer arch around the same as the barrel arch. Again this adds a little thermal to the sides, but unsure of how much of an effect. Maybe I am overthinking things. I have very experienced commercial masons doing the install, but they don't have much experice with heat being applied to a barrel shape (only fireplaces). They don't seem concerned at all. When they built the barrel they used no side reinforcement (just let the walls sit for a couple of hours) and the arch forms were removed immediatley (looks great). Thank you very much for your advice as well as any others out there who may have an opinion. I will post pictures of the project when time allows.

Dutchoven 07-22-2009 05:57 AM

Re: AS Oven Question
I concur with Neill in that it would be sufficiently buttressed...but you may consider some type of layer that is a bit more compressable than the the very outside of the insulated cladding...otherwise there might be possibility of cracking your outer brick walls when the oven fully expands...

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