layout question-review of layout

[CapePizza]

I'm trying to figure out what's the largest oven I can build that would fit on the hearth I have to work with which is 52 inches in width. I've attached a sketch of what I think will work but asking for feedback if this looks correct. Please let me know any comments, changes, suggestions, etc.. Thank you for the help.

[UtahBeehiver]

How are you laying the dome bricks? The drawing seems to show the brick layed in the wrong orientation. Typical bricks 2.5" thick by 4" wide by 9" deep. A brick dome should be half depth brick or 9 brick cut in 2 (4.5") .or if a half soldier then on the 4" width. This affects you max. dome dimensions.

[CapePizza]

Thank you for your comments. Not sure what I was thinking when I roughed that out. I've attached an updated sketch. This shows the "soldiers" in, what I think, the correct orientation. I plan on using half soldiers placing them on top of the herringbone floor. The supplier where I will get my bricks has firebricks that measure 8.4"x4.2"x2.35".
Couple of questions: would it be better to increase the pcrete thickness to 2 inches and lessen the stucco thickness to .5"? Also, is an 18' opening too large, too small.... or okay?
Thank you again for taking the time and looking at this.
John

[david s]

The dome bricks are normally cut in half and laid so the dome thickness is 4". The sides are usually bevelled.

[UtahBeehiver]

You might be able to get away with 1/2" stucco, normally three coat stucco is a min of 7/8". Have you poured the hearth? If not you can cantilever slightly to give you some wiggle room. The outer dimensions have a way of growing. Also, there is nothing magical about oven ID, I could be a 31" as well. Inner arch width is sort of a builders choice. But the height of the arch should be about 63-65% of the dome height. Forno Bravo plans show a 19" wide opening for a 36" ID oven.

[CapePizza]

Thanks very much to you both for your follow up comments.

DavidS -- is the attached image more like what you were referring to when you say "the sides are usually bevelled?

Russel, I was thinking of reducing the oven diameter even more in line with what you are noting... maybe even go to 30 inches. The hearth already exists so I have to deal with that as a given (52 inch width). It wouldn't necessarily be pretty, but I also thought of overlapping the hearth's edge (extend out from the hearth) the pcrete layer. It would only only be at the tangent points at the hearth's sides so maybe an inch or two out from the hearth's edge. Maybe that's what you meant by "cantilever slightly".

Thanks again for the help.
John

[UtahBeehiver]

I meant cantilever the concrete hearth if it has not been poured. You should not cantilever the p/vcrete since it does not really have sheer strength. Under the floor the ratio should be 5 to 1, dome 8-10 to 1.

[CapePizza]

ah.... okay. thanks. The hearth is already "cantilevered" a bit. I previously had a cob oven built on the stone pedestal. The weather here doesn't jive with the cob material as it's pretty hydroscopic. The dome collapsed after a few years of sucking up the moisture. So rather than build a new pedestal, I'm trying to make due with the current. Building a brick oven hopefully will be more friendly with the moist environment here. I'm figuring most of the weight of the dome will be over the pedestal. The hearth is 5 inches thick with rebar, so hopefully will hold up under the weight.

[UtahBeehiver]

I notice you have not talked about insulation under the floor, The floor must be isolated from the concrete hearth with insulation or hearth acts as a heat sink.

[david s]

[QUOTE=CapePizza;n426203]Thanks very much to you both for your follow up comments.

DavidS -- is the attached image more like what you were referring to when you say "the sides are usually bevelled?

Yes. Here's what I meant.

Also your floor bricks need only go out as far as the outer edge of the inner dome, or if building the dome around the floor instead of on top of it, to the inner face of the dome bricks.

[CapePizza]

For the floor insulation I'm planning on placing 1" panel of foamglas on top of the hearth and top of that 2" FB board with the cooking floor firebricks on top of that. The one thing I'm grappling with is weep holes and whether I should create them under the foamglas. I didn't account for weep holes when I poured the hearth so if they're necessary, I'll drill through the hearth 5 or 6 spots. Still thinking about it.... any thoughts would be welcome.

Thanks for the sketch, DavidS. I see some folks cut each brick with those tapers for each row and other's seem to fill in the gaps with mortar. I guess from what you're saying by showing the sketch, it's better to have as much brick to brick contact, rather than have all that mortar (which is probably not as strong as the brick and also taking into account expansion and contraction when the oven heats up/cools down) a packing of mortar might fail over time.

[UtahBeehiver]

Have you been able to source 1" FoamGlas? Unless they have changed, min. thickness if 1.5" Foam Glass being not hydroscopic, weep holes are optional but best to have a few for means of any water having a way to egress out.

[CapePizza]

Grainger seems to have 3/4 inch foamglas available. However I'd like to have 1 inch or more preferably, 1.5 inch. There's a supplier in my area who sells it and they're looking into the thicknesses they have available.......

[UtahBeehiver]

3/4" flat or are you talking for pipe? I thought Grainger only stocked foamglas for pipe.

[CapePizza]

3/4" flat. I've attached a screen shot. I just heard back from the local insulation supplier. They can get "cellglas"... which I'm trying to clarify with them if it's the same as "foamglas".... they can get 2 inch sheets, each 18 x 24" for $23 a sheet. I'll probably go with that.