Michigan Mobile Oven Build

[skeleturtle]

Hey everyone,

I am currently working on a mobile Cob style oven with a friend. I attached where we are with our trailer. Currently we are sending it out to get the brakes/lights all wired up before we start the oven build. I do have a few questions if anyone cares to help.

Plan:
4 inch Slab - Does this need to be refractory concrete, or can we just use quikrete?
4 inch of Super Isol insulation board - I found this to be expensive and have not seen this exact type of insulation on Home depot/lowes websites. Is there a type of insulation board I can pick up at Home depot, or am I stuck ordering the Super Isol insulation board online?
Medium duty fire brick - We found a local place in Warren MI to pick this up.
4inch thick Oven Dome - The plan was to do a cob style oven, is there a specific recipe anyone could share that I can follow? I've seen recipes for mortar, but am not sure if this would be good for entire dome, or just a way to seal the bricks for Pompeii ovens. Our plan would be to use a mound of sand/paper to build around, add about 4 rebar posts which would go into the cement slab to help secure the oven down. After 2inch layer of Cob add rebar mesh/insulating blanket then add another 2 inch final layer.

In the photos you can see our "Box" has an open bottom, but we recently put steel in the bottom to support the slab, there are seams for moisture to escape, but we may need to drill a few extra holes as well. The inner box for our slab/insulation is 54X61 and we added an extra lip for the fire brick which gives us 58.5X65.5.

I will keep posting updates, thanks for looking and feedback!

-Dan

[david s]

One of the main problems with ovens on trailers is bouncing and vibration. It would be a good idea to add shocks to the trailer. I doubt whether cob is a suitable material because of this. A proprietary castable refractory would be a far better choice because it's more durable. If cost is a problem you could try using the homebrew mortar mix as.a castable. 4" thick will take a long time and more fuel to get to temperature as well as being heavier. Most cast ovens are around 2" thick. Because the oven floor is separated from the supporting slab by insulation, standard concrete is fine.

[skeleturtle]

Thanks David!

I will look into the homebrew mortar mix and talk to my partner about doing a 2 inch thick dome vs the 4 inches. I'll also talk to him about the shocks.

Appreciate the input!

[UtahBeehiver]

David Sis one of our leaders on cast ovens so take stock in his advice. He also does mobile builds as well so he has practical experience with the issues of transporting mobile ovens.

[david s]

I kept mine lower than I would have preferred for cooking because I didn't want a high centre of gravity when it's sitting in the trailer. Apart from cornering, this problem is further compounded if the trailer has a single axle. If the trailer is not hooked up to your car then the drawbar can go skywards as the load is shifted rearwards.if the drawbar is lifted. This happened to me on a couple of occasions. Fortunately as mine rolls on and off the trailer on a trolley it was a simple matter to shift the centre of mass a little further forward. The weight of the oven should also match the spring rating or you may need to boost the springs.

[skeleturtle]

The springs should be good, perk of having the trailer custom made we were able to explain exactly what we needed and got an axle rated for 5200 lbs. Custom trailer for the same cost of a standard trailer was a happy investment

[skeleturtle]

Hey guys,

It's been awhile since I have had an update. It's been a very slow process. We currently have the 4in slab down in the trailer, and are still looking locally for a high temp Insulation board or block for the sub floor. I was curious about your thoughts on a Steel dome such as the Forno Bravo Bella model. For a mobile oven it seems to make sense, as we wont have to worry about the oven breaking from all the wear and tear from the road. It would also allow us more cooking room if we go with the half cylinder shape versus the circle dome. My only concern is insulating the heat, currently we are thinking of doing two walls, with a small gap between the two. Inside the air pocket we are thinking of throwing in an insulation blanket. We are then thinking of adding an inch of hombrew mortar mix to help hold in the heat a little bit more than a traditional steel oven. There is a concern however with how the two materials would interact with each other.

Any thoughts on this construction style?

[david s]

Yes, because the steel is way more conductive than its surrounding refractory it will expand first and almost certainly crack the refractory over the top. This doesn't matter that much because the insulation wil hold it all in place. Why don't you discuss your needs directly with FB and see what they offer/suggest?

[skeleturtle]

Good Idea I'll shoot them a message thanks!

[skeleturtle]

Well it's been a slow process but we now have to the Slab and the Calsil board in and ready to go. Next weekend we hope to pick up the fire bricks. The rebar sticking up is for the oven dome, but we are contemplating doing a steel dome, since this is going to mobile we figure that would be a wise choice. If we do go steel then we will cut the rebar sticking up.

[skeleturtle]

Hey,

So we are currently waiting on a quote for a Steel dome. My brother created the file attached. basically we will be using stainless steel for the inner and outer layer with 4 inches of insulation between. We will have structural steel between them where we will bolt them together and to the steel frame of our Trailer.

Does anyone know if this could cause too much thermal transfer between inner/outer dome and the Structural Steel to the steel of the trailer?

Thanks!

-Dan

[david s]

I'd be more concerned about the floor design. You seem to have dense floor bricks extending out from the vault interior. The whole of the oven interior should be encapsulated in insulation. There also appears to be very little insulation under the floor bricks.
Not sure how thick the inner stainless steel layer should be, but a highly conductive material like stainless steel will lose heat very quickly. I suspect something thick like 2 mm would perform better than thin stuff. Stainless also buckles lots when heat applied.
You will also need to fix the outer steel shell to the supporting slab, especially because it's mobile. Look forward to hearing how it goes.

[skeleturtle]

We currently, have the design so the inner steel shell is sitting ontop of a firebricks, under those firebricks we have 4inch of insulation, and a 4inch slab. Around the inner shell we will have 4 inch of insulation blanket. Extending out from the inner wall we do have firebrick with no insulation, but we assumed this would be fine because the inner dome was fully encapsulated by insulation. We werent going to have the outshell fixed to the slab, but instead have it bolted to the frame for easy attaching and removal. Our steel is also actually 316 Steel compared to the bella 304, I'd have to check the bella's thickness but I believe our design would be thicker using 12ga steel. Would this not suffice?

If the above sounds like it should be good, it sounds like you aren't concerned to much about heat transfer from the inner shell to outer shell and to the trailer than?

[david s]

That sounds ok, but the floor bricks should not extend past the inner shell.4" of blanket between the inner and outer skins is fine.outer skin can be thinner, say 0.9 mm (19 ga)

[skeleturtle]

Awesome, thanks for the feedback!