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ThermoJax 09-19-2010 09:59 AM

ThermoJax's 42 oven
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After 4 years of lurking, reading, planning and talking about it, I started cutting last night. So fun. Firebrick cuts pretty easy. I have my soldier course cut and dry fit. The oven floor is now round. I think I could mortar the soldiers now, or cut my inner arch. Does anyone know if the bricks on the arch proper need to be cut into a wedge shape, or are the good to go as is? My android phone alerts me to email, so I can monitor any responses out at the job site. So many new skills to learn, including how to make pictures smaller to post. I will try to post more this evening to catch up to where I am. Thanks for your advice.


SCChris 09-19-2010 03:12 PM

Re: ThermoJax's 42 oven
Regarding bricks in the arch, I tapered both sides to create wedge bricks. In conversation with "Giannifocaccia" John, I told him that I think I'd build my next inner arch laying flat, with the inner arch against a dead flat surface of 3/4 inch plywood with plastic on top of the ply but under the bricks, the plastic is for later release. Once built I'd rotate the arch into position using the plywood form as support.

My reasoning is that building the arch flat assures the door rebate is dead flat as long as your brick cuts are clean and you don't allow mortar to hold a brick high. Additionally that each brick sits flat against a supporting floor keeps the stress on the adjoining bricks in the arch to a minimum until the mortar dries. I'd build the form and mark exactly where you want each brick to sit in the arch and what the grout joint should be between the bricks. If you have a few voids on the back side of the arch they can be filled once the form is removed. I'd love to see James create a precast inner arch with a matching insulated door and an included FB "through door" thermometer. Sweet! All of this said I have never seen an inner arch built flat and rotated into position.


PS - Whatever you do with the inner arch make sure that you can remove the building structure arch supports without disturbing the completed arch.

ThermoJax 09-19-2010 04:48 PM

Re: ThermoJax's 42 oven
Thank you so much for responding. I think I can do the rotate the board up with the arch method, and look forward to trying. I am really sold on the idea of about a 1/4 inch gap as a heat break between the inner arch and the landing and associated vent area. Have you some thoughts on accomplishing that task. Pizza Bob's build incorporated the arch build/vent area into the inner arch, perhaps canceling any heat break. I have tons of insulation to fill that gap. All are welcome to opine. Thank you for your accumulated wisdom.

SCChris 09-20-2010 09:01 AM

Re: ThermoJax's 42 oven
I wish that you were local to me so I could be more available to help out.

Remember that there is no perfect oven, and my point of view is just one of many here on the FB forum.

John with the board name GianniFocaccia is about the same place you are with your build and he’s also looking to include a thermal break in his oven and later his brother’s oven. He’s going to be a great resource for you to bounce your ideas off of and you in turn can help with your POV. Watch his build and ask questions, you’ll get plenty of feedback. Fxpose, included a thermal break so make sure that you take a look at his build. Checkout what Fxpose did with his break, in “My 3-Legged Dome” and see if some part of it makes sense for you, post 44 in his build.

As you might have gathered I prefer the insulation board over the IFB and I think you'll be happier with the product. My opinion is that it will last longer than the IFB.

Most of us here have an incorporated inner arch / landing / vent structure, me included. I think time will prove that a well designed thermal break is much more desirable but it is a bit more complcated.

What a full T break does do is to make this outer structure, the landing vent area independent of real support from the dome. What you end up with is an open top barrel vault with some arch structure on both ends. The arch portions of this area don’t really do much supporting, the side walls take the chimney load. What you’re left with the aesthetic front arch and a rear structure. You’ll do your best to seal the rear so as to force the smoke and waste heat up the flue. Fx avoided some of the problems by casting a vent area, post 60, and then mating it to the oven. This made the walls only support for the vent casting. I suppose he could have just glued the vent in place with high temp gasket material if he had wanted to.

I’m not clear if he used any IFB in this area of his build but he used it lower in the walls. He then applied stucco over the front of the casting to integrate the look with the rest of his oven, post 74. Fx also sidestepped the arch building by using a steel lintel to support the dome at the oven entry.

You have indicated that an inner brick arch is what you want and you’re game to try to build it flat and then rotate it into position. I think there are 5 points in the inner arch entry structure that are critical.
  • 2 at the leg bases, these should be on the identical floor plane and these support legs should be parallel to each other, vertical when rotated into position.
  • 2 more points, where the arch meets the legs these points should ideally be at the same height.
  • 1 more, the Keystone should be at the top center of the archway.

So since your building on a flat surface you need to focus on the bricks at the leg base, the bricks where the leg and the arch meet and the keystone. I’d try to use some temporary structure to clamp the keystone and leg bases rigidly in place. I’d set parallel boards on the inside or outside of the where the leg bricks will go to assure these bricks will be vertical and to keep them from being pushed out of alignment during mortaring. When you have your bricks mortared in place cover them with a damp towel to maximize the strength of the grout, keep this towel damp for a few days.

After the mortar has time to cure, a week would be ideal, and before you rotate the structure make a template for your door. You want this template to last for years so cardboard or ¼ inch plywood or Masonite would be ideal. Your first door isn’t likely to be your last but hopefully the template will be.

If you find that you have a crack in the arch structure, remember that cracks are pretty normal and as long as it isn’t to the point where a brick is going to fall out you should be fine. Also remember that as you tie in the dome this arch will be more stable. If you think into the future of the dome part of the build when you create the entry’s temporary structure this structure could stay in place until you have dome bricks tied to the archway. It would certainly provide a bit more support until you get the dome tied in and this wouldn’t be a bad thing.

Very important! Make sure that you plan for the structure’s removal in such a way that it doesn’t stress the finished entry when you remove it.


PS. Remember that there is no perfect oven, and my point of view is just one of many here on the FB forum.

GianniFocaccia 09-20-2010 01:30 PM

Re: ThermoJax's 42 oven
Thought I would mention that since you are planning a stand-alone entry to facilitate a heat break, you may wish to refer to the 'angle of thrust' page offerred somewhere here on the FB site. Sorry I can't provide the link. I will be going with a hemispherical entry for the aesthetics, but also because of the strength.

Some of the builders here have massive, double-thick brick entries that not only look good, but also provide the necessary arch anchor mass to accomodate vertical walls, effectively accomodating the arch side thrust. This type of config would not hurt an oven with a heat break, and in fact, with the added mass, an entry heated solely by exhaust gases might prove beneficial in providing a lower dome-to-entry heat differential.

SCChris 09-20-2010 01:37 PM

Re: ThermoJax's 42 oven
The "angle of thrust" subject sounds like Dmun. He had included some information on Arches and the physics associated with them.


ThermoJax 09-20-2010 01:50 PM

Re: ThermoJax's 42 oven
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Well, this is kind of based on drseward's build and Scchris ideas. I probably should cut them into wedges. They are all 1/2 bricks. The bottom stir stick is cut to 20 inches and the little stir stick is 12 inches. I can't find the angle of thrust post, I did a scan of Dmun's threads, but no joy. I have cut my second course using Hendo's method. Appears tight, but not glued down yet till I lick this inner arch problem.

ThermoJax 09-20-2010 01:55 PM

Re: ThermoJax's 42 oven
1 Attachment(s)
this shows part of course 2, dry fit, not mortared.

ThermoJax 09-20-2010 03:19 PM

Re: ThermoJax's 42 oven
Ok, I have most of the arch cut to wedges and am ready to glue em up against the plywood (leftover from the stand build). I can't imagine waiting longer than tommorow morning before I hoist em up. Maybe a blowdryer on the joints. It almost seems like an arch wants to "settle" rather than perhaps relying on the less robust mortar holding a wedge piece in the arch, artificially high, when, if it "settled" so you had brick to brick in a wedge, then one day, that mortar might give inside that one brick that was not brick on brick. Perhaps it falls down into the wedge position and all is fine, or maybe the whole thing comes tumbling down. All in all, I like the idea enough to do it. Unless....

ThermoJax 09-20-2010 03:40 PM

Re: ThermoJax's 42 oven
1 Attachment(s)
here is a shot of the arch before mortar. Very ugly wedge cuts, but , but... I might cut some of the unneeded plywood away. Perhaps in the shape of a U, but maybe I need that middle for stabilization whilst moving.

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