Steel oven ceiling

[jinsko]

Hi everyone. This might be a stupid question, but... I have converted a wood-burning stove into a pizza oven. It works great. But I have decided to create a new ceiling for it, which I cast out of refractory. I did it in 4 sections thinking I would mortar them together. As you can see from the photo inside the oven, the ends rest on steel pieces that span the oven.

My question is this: if I just mortar the two pieces together (using Heat Stop 50) is that going to be strong enough to keep the "arch" together? Or is is it just going to collapse at that joint and fall on to my hearth? It's pretty heavy...

Thanks in advance for any advice.

-Jeff

[Toomulla]

the panels will need support in at least one direction ( the ends) they will not self support in the manner of a true arch or barrel vault. the design as an apparent barrel vault is not a true reflection of the actual construction which appears more like simple span slabs.

[jinsko]

Thanks, Toomulla. But I'm not sure I understand. I never meant to design them like a barrel vault. I'm asking about support in the middle. Either end will rest on the steel supports (one of which you can see in the picture). I'm asking if mortaring the pieces together will be enough to keep them from collapsing. I would mortar them in the center where they meet (as pictured) and also mortar them side by side and against the oven walls.

[dakzaag]

It will work until it doesn't which will probably be when the side channel rusts out and fails. I think you can mortar them together and I would form them higher then what looks right so that when you pull the supports, they have a natural spring already. Use shims in the support forms so you can slide the shims out and pull the supports without pushing up on the pieces.
After the work of making pieces, I wonder why you didn't just cast the dome in place and be done with it? Either way will probably work until the iron rusts out.

[jinsko]

Thanks, dakzaag! I am hoping it will be a good long time before those side pieces rust out. They're pretty thick. And I appreciate the tip about shims and forming the supports high-- very helpful.

The reason I didn't cast the dome in place is because I couldn't really figure out how to do it. It's pretty tight in there and I would have been shoving the mix in sort of sideways through the door of the oven instead of pouring it. Maybe that would have worked after all? Too late now, I guess... (Of course, the other reason is that I don't really know what I'm doing and am making this all up as I go!)

Btw, where are you in Indiana? I'm a native Hoosier myself.

[dakzaag]

Monon if you know where that is I'm about 5 miles north.

I don't really get your description of the cast challenge, since you had a basic arch that you used for the pieces, why not put that arch in place over the metal, leave the top open and pour in the castable? It doesn't matter now, you have the pieces made up.

Another thing, if you have ceramic paper or ceramic insulation, put a thin layer of it between the cast pieces and the support iron so there is a slip joint. The metal will expand and contract differently than the cast throughout the heating cycle and the non flammable material will keep the pieces from binding. If you have nothing else, common fiberglass insulation will do but you should be planning to insulate this thing so use some of the insulation as a gasket.

The more you protect the iron from heat, the longer it will last.

[jinsko]

Thanks. I know where Monon is; grew up in Lafayette.

To explain the casting issue: there is no top to leave open. The oven is completely enclosed (and insulated and covered). The only access is through and it's not possible even to get the arch in there and onto the metal pieces. In retrospect, I probably could have turned the stove upside down and poured an arch, but that ship sailed long ago.

Great tip on the fiber paper as a gasket, though! I will most definitely do that. Thanks.