42" Pompeii construction in Adelaide

[P3 Stoaker]

G’day all
can anyone tell me what a typical thickness of render might be for rendering a vent arch? My thought is for the upper horizontal layer of the vent brickwork to over hang ???5-10 mm (quarter inch ) or so to accomodate the thickness of the render.
Im going for 2 inch of blanket over the dome, then 2 inch vermiculite over that with render then over the the lot including the vent/arch brickwork. I understand there is no need to insulate the vent brickwork.
Thanks in advance.
Regards
Greg.

[P3 Stoaker]

G'day All,
Russell, David S and Mark, many thanks for the comments and advice, greatly appreciated.
I've cut some full bricks so as to form a flat surface. They will convert from the rectangle shape, wider than needed to a round shape about 1.25 inch greater diameter than the 8 inch i eventually want, and the next layer will reduce down to correct flue size. Not sure if it would have been an issue but I didn't want flat horizontal spots in the vent brick work where exhaust would tend to slow or be trapped. Probably an overkill but bow it will smoothly transition from rectangle to 8 inch. Photo's to follow. in the end around 100 lbs.
Regards
Greg

[MarkJerling]

Gday all. Has anyone ever considered the weight of the bricks added on top of the entry arch so as to form part of the fluing? Initially I planned to cut curves to form a flat top, which I’ll still do but I was going with one more layer on that before installing the metal flue. I haven’t actually weighed the bricks but that could add to nearly 50 kg, or even more around 110 lbs.
Appreciate any thoughts or experiences.
Regards
Greg.

As David has said, yes, one needs to consider the thrust on a segmented arch. (With a full half-round arch, it's less of a concern) With my oven, I buttressed the (segmented) arch with a second layer of bricks set back from the outer door face, so it's all hidden behind my insulation and plaster. As yours is a full half-round arch, I would consider it less of a concern.

[MarkJerling]

G'day All, thought I'd post a few picks as the pics others have posted have been a great help throughout planning each stage of my build. Going slow but still progressing.
Regards

That looks fantastic!

[david s]

No it’s easy enough to get double wall here. I’ve done a couple of ovens with double wall but used standard coated steel (Colourbond) for the outer pipe, inner one stainless. You just need a cowl at the top that is made to take the two different diameters. I also stuff some insulating blanket between the two pipes for the first foot or so of pipe height.

[UtahBeehiver]

David brings up good points so it depends on your situation. I do recall that it is more difficult to get double wall SS in Australia and many builders have had to import in from the US.

[david s]

I can’t entirely agree with you Russell re the double flue. As the stainless is expensive a double flue raises the cost considerably. Of course if it penetrates a roof and is anywhere near timber you need to go double or even triple, but if it’s outdoors then it’s not necessary. The location of the flue is well out of the way to be a danger for little kids to touch. The flue’s only purpose is to keep the smoke out of your face. In fact the oven would work just as well if it had no flue as some cob ovens operate this way.

[UtahBeehiver]

Since you have a full arch, the outward pressure will be more vertical than horizontal. I have a set up similar to what you are talking about with no buttressing. 8" ID double wall is just fine for a 42" Double wall reduces the outer temp considerably and more for safety issues than performance issues.

[P3 Stoaker]

Thanks David S and thanks for the earlier comments Russell. David, I agree that two rows seems like it would be ok but who really knows. I’ve confirmed the weight of 50 kg or around 110 lbs. the question is would the extra weight help keep it all stable or exacerbate any cracks/ movement, hard to tell.
Russell, the cuts have been fairly straight forward after seeing what others have done. I’ve actually enjoyed forming the arch, the dome was also good to do but took quite a while.
Additionally can anyone advise, for a fairly standard 42 inch oven, is there any advantage in going for a 10 inch flue over an 8 inch, and being fully outside, is double skin recommended?
many thanks.

[david s]

If there's too much weight on the arch the sideways thrust on could make it fail. The remedy is to support it with buttressing. The question is how much weight is too much? At a guess I'd say you'd probably be quite safe with two rows of bricks on top of the arch.

[P3 Stoaker]

Gday all. Has anyone ever considered the weight of the bricks added on top of the entry arch so as to form part of the fluing? Initially I planned to cut curves to form a flat top, which I’ll still do but I was going with one more layer on that before installing the metal flue. I haven’t actually weighed the bricks but that could add to nearly 50 kg, or even more around 110 lbs.
Appreciate any thoughts or experiences.
Regards
Greg.

[UtahBeehiver]

Sure got a lot of fancy complex cuts. Looks great, the turtle wins the race with these ovens.

[P3 Stoaker]

G'day All, thought I'd post a few picks as the pics others have posted have been a great help throughout planning each stage of my build. Going slow but still progressing.
Regards

[P3 Stoaker]

Thanks Russell, seems to be going OK.
The big thing I noticed with this arch was I positioned the front face of the form accurately so able to lay the bricks flush with the form. I did read about doing this but failed to realise how significant the advantage would be when laying the inner arch. This time it has made getting the front flush nice and easy and well worth incorporating in the plan.
Regards

[UtahBeehiver]

Looking good as always. Nice solution on thermal break.