brickless dome on a shoestring oven

[michelevit]

Here are some pics of a group build pizza oven that was inspired by an oven I built last year. Budget is non-existent. Another money poor, time rich project.

The floor is recycled fire bricks ($O) arranged in herringbone pattern.
The mold is made from a 5 gallon bucket surrounded by wine bottles, beer bottles and beer cans buried with wet sand. Wrapped with flour soaked newspaper to keep the sand from settling.

Here are the pics which describe it better...

Build gallery here...

Gallery | bricklessoven

Next steps is to tack weld a rebar cage around it and bury it in DIY high temp mortar . (cement, fireclay, lime, sand, sand, sand)
Once the high temp mortar cures we'll sweep out the sand, bottles and begin slow curing.

Any advice or comments are greatly appreciated. We're hoping to have it completed by new years which is only 22 days away.

[Fish Wheels]

I'm very much looking forward to seeing and hearing about the results

Good Luck
Rod

[michelevit]

Spent a couple of hours cutting up rebar and tack welding a mad max reinforcing cage
around the sand mold.

pics below.

next step, fab some sort of flue and pack on the high temp mortar.

[dmun]

We're watching this with interest. Rebar isn't usually used with castable refractory, but of course you're not using that. I don't think anyone has used the homebrew mortar mix for a casting like this: It'll be interesting to see how it turns out.

Are you using an external form, or just piling it on?

[michelevit]

do you think it will work?
any advice or opinions is greatly appreciated.
The plan is to mix the DIY mortor with minimal water
and pack it around the sand mold.

more pics here...Gallery | bricklessoven

[dmun]

do you think it will work?

You are in uncharted territory: Your danger is cracking, and it may not be that much of a problem. In theory, mass is mass, and as long as it holds together it should work.

The short answer is: I don't know. I wouldn't spend a fortune encasing this oven until the concept is proved.

Remember, it's a LOT of wet concrete, and it will take a long time to cure, and even longer to dry and get up to temperatures. I'd take it slow to minimize cracking problems.

[cynon767]

Originally Posted by dmun

Remember, it's a LOT of wet concrete, and it will take a long time to cure, and even longer to dry and get up to temperatures. I'd take it slow to minimize cracking problems.

I'd second this... especially considering the low temps we're having right now in northern California, it will be a pretty close call to have it done by new year. I would definitely let it cure for several days, maybe a week, before pulling the mold, and then bring up the temp gradually before firing. Try using a halogen shoplight for a few days before moving up. I also used a propane burner for several days, gradually increasing the temp before switching to higher heat wood.

Using the DIY mortar as a small-aggregate concrete is doable, but it needs a good reinforcing matrix to substitute for the gravel that concrete typically has. In most cast-concrete applications, it's done with the rebar/wire/lath approach you're taking. The only problem I can foresee is that there's a possibility that the rebar itself will expand at a different rate when heated than the concrete around it, and could actually cause cracking; even if it does, though, it's better than an unreinforced dome. Worst case scenario, as far as I can tell, is you have a dome that cracks along natural fault lines into segments which are all held together by the rebar. You could also consider the possibility of adding further, finer-scale reinforcement, possibly in the form of something like chicken wire, to help with stability. I don't know enough about this to say definitively whether or not this would help in this instance, especially considering the heat factor, but I do know that it is the sort of thing that is used in other complex-shape cast concrete pours, like planters and countertops and such.

Good luck... let us know how it goes!

[JoeyVelderrain]

I know it has been said but I just want to reiterate, the rebar may be a problem since the castable refractory will want to expand and contract with heating and cooling, this is why I built my dome in two sections, the soldier wall bottom section and the dome top section. Even so I still got one good crack in the dome about 12" long.
looks like a fun project, good luck with it.

[michelevit]

Its always been my understanding that rebar and cement have the same coefficient of expansion and will expand and the same rate. When crack occur the rebar lattice will
keep it from collapsing.

We're pouring wax over the sand to seal it and keep it from absorbing the water
from the wet high temp mortar. We were going to paint it, but have access to free wax
and it dries hard much quicker than paint would.

[Neil2]

"Its always been my understanding that rebar and cement have the same coefficient of expansion and will expand and the same rate."

I assume you mean "concrete" instead of "cement". (Cement is the powdery substance that , added with aggregate and water = concrete). Yes they have about the same coefficient of expansion (8.0 and 7.3 )