31"/800mm in Eindhoven, the Netherlands: Design critique and build topic

[Toiletman]

What happened at the top of the cast?

As mentioned and shown in posts #71/#72: I mixed the concrete too wet and it was slumping down, so flowing out of the top part of the cast. I now have more thickness at the bottom than planned, and had some gaps at the top. I filled them in again, and they're now damp curing... my feeling is that it's good enough to hold up and provide sufficient surface for the chimney connector to sit on.

I am a bit perplexed when going back over this thread. Post#65 shows pics of the top of your flue gallery arch. With your casting sitting on top of it, the slot in the top of the arch becomes redundant and a restriction for smoke flow. I was under the impression that your casting would replace the brick arch. I think it will still work ok as you propose, but not as efficient as it could be.

I did consider a fully cast gallery arch initially, but since the gallery is so wide to accommodate the barbecue area and the arch has such a shallow curvature I thought it would be very challenging. Having a small thickness would probably not have enough strength, and making the cast as high as the brick gallery would make it very unwieldy to manufacture and transport. I also like the look of the brick arch face a lot.

You are right about the shape of the bricks becoming a restriction. Not fully a restriction, as the the smallest surface area is always the chimney pipe, anything upstream is wider. However, the widening of the brick arch will cause a negative pressure gradient which might cause some recirculation. Overall though, from the cross section I think it's still smooth enough. Especially if you consider the lengthwise cross-section: the vertical path in the middle of oven is very straight and smooth, it's only at the sides that the recirculation might cause a decrease in draft.

Attached some pictures of the cross sections, as well as an alternative design I considered fully covering the brick arch with a casting --> in the end I felt it would only add to the complexity of construction and make the casted part less robust --> the only material that's really needed is the material to sit around the smoke opening. My main worry was about the brick arch being able to support the weight of the casted part, that's why I thought of extending it to be supported on the gallery walls. In the end my feeling is the gallery arch should be able to support the weight, as well as that once the vermicrete plaster is in, it will provide a nice stiff surrounding shell, with a lot of height giving it also a lot of stiffness, probably eliminating the problem completely. Feel free to chime in with your thoughts...