Cast your own
I'm probably opening a can of worms and hope this hasn't been discussed elsewhere. Has anyone tried using casting refractory cement over a dome of foam. I was thinking that with the base, hearth and cooking surface in place one could place a foam dome shape, probably covered with some sort of plastic sheath and an appropriate front opening accounted for, on top and just trowel over it. Cut out the foam and build a vent. I'm not a mason by any means, so pardon my simplistic approach.
There's no reason why this couldn't work, but there are two problems. Refractory cement in thick applications takes forever to cure, and it's strength is problematic. I know that the rumford fireplace guy gave up on casting his curved throats from refractory because it took a month before enough moisture was gone that the customer could build a fire. I've noticed around here that folks want to fire up their new ovens sooner rather than later.
Also, fire brick has an attractive brick-like appearance while cast refractory looks like, well, concrete.
Someone was discussing plans for something called a "loam" oven:
The same sort of idea, I think. Building an oven is a lot of work. Why not get the best?
Thanks. I'm early in the planning and was just wondering. Just out of curiosity, what are the precast ovens, like the ones on this site, cast from?
Firing up sooner is a good thing!
Modular ovens are made from a high-alumina clay, like the firebricks are made from, and then fired to thousands of degrees to vitrify them. It's a very different process than refractory cement. The reason they come in pieces is that there are production difficulties with firing huge fireclay segements, to say nothing of shipping them.
David's description is very good. The materials, processes, and infrastructure our producer uses to make precast ovens are all quite sophisticated. They have three decades of experience and are the world's biggest producer of precast wood fired ovens. You have to remember that we make more pizza ovens every couple of months than the largest U.S. producer has ever made - in its entire corporate history. We (the new world) are really catching up on this front.
For a homeowner making a backyard oven, you have a number of choices. Our precast Forno Bravo ovens (and Artigiano brick ovens) are great. Still, if you want to build your own, and don't want to buy an off-the-shelf oven, you have more choices.
You can build a brick oven. You have the advantage of using firebricks, which are a domestically-made product that work very well for pizza ovens. The Forno Bravo brick pizza oven plans are free, and very well supported on this forum.
Or, there are other options. There are adobe, loam and refractory ovens, and probably others. Really, any pile of bricks will absorb heat, and cook a pizza. They say the Greek infantry cooked pizza on their shields. One of our Italian rental houses had a field stone oven -- dome and floor, without a brick in sight.
That's the good news. You get to pick how you want to do it. Have fun and enjoy the roast.
Lots of info. Thanks a lot for the education and your time.
Casting your own
Just want to say great forum, just stumbled on it a week ago. I might be a little late with this response, Cam I did cast my own, A friend and I built an Iglo 2 years ago out of styrofoam blocks shaped it into a dome with the opening and flume hole. Built a wood base to give a 3"-4" thick walls. We had to add a fiberglass skirt to hold in the refactory so it wouldn't slide down. Did alot of experiments on the foam because we wanted to cast many using the same mold so I coated it with metal aluminum tape. Upon casting I coated the tape with a vegetable shortning since I wanted the mold to release easily. We built the first one last year and it works like a charm. We have built the second one using the same mold but I have not installed it yet, waiting for the spring. Hope that helps.
Cast refractory concrete
Some years ago I worked for a company that manufactured gas fireplace inserts and burners. For the logs, we cast refractory concrete in latex molds. The cement used in the concrete was a calcium aluminate one manufactured in France and sold under the name of FONDUE. Cure time was 72 hours in a gas fired oven at about 150 deg. F if I remember right. The logs could be subjected to fire immediately after they were cured.
One more thing
I forgot to mention that unless you enjoy research and development and have lots of time to do a proper job, I can't think of any good reason to want to build an oven of refractory, or other concrete over any sort of mold when perfectly wonderful modular and pre-assembled ovens are available from Forno Bravo as are plans for their Pompeii brick ovens.
Castable Refractory Kilns
I found a link describing how large kilns are cast and I thought you all might find the information interesting. http://artistpotters.com/anagama/castable.htm
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