48" Mobile Oven Build

[david s]

A 5” inner pipe is inadequate for a 48” inner diameter oven. You need an 8” pipe. My understanding was that a double flue was only required if penetrating a roof space, but you’ll have to follow the rules provided by your local authority.

[nuovopizzas]

Thanks for the pictures David.

For my health codes, I need to use a double walled chimney. Will I still be able to use your method. This also means that the outer diameter of the flue is 8" while the inner diameter is only 5". Do you foresee any problems with this flue size being too small?

[david s]

Finished removable flue.

I forgot to add I also make 3 little tags at the bottom of the sleeve to prevent the pipe sliding too far down.

[david s]

For a mobile oven you definitely need to have a removable flue. You don't want the thing flapping around in transit. I've done at least half a dozen of these and developed a simple method by making a sleeve into which the flue pipe can slide. I'll let the pics tell the story. You may develop a better or simpler solution so post what you come up with to assist others.

[nuovopizzas]

Today, 2 weeks post cast, I removed some of the form to get a peek at the inside. The fiberglass is slightly transparent so I can see that the interior of the dome, and it is void and crack free, thank goodness.

I think David's suggested 3:1:1:0.5 blend was a very good one, with stainless steel and AR reinforcement. You can tell that its very binding, especially on little bits that come off. When there's a stainless steel needle going into it, it provides so much strength to the cement.

There are a few mistakes here and there that if I were to do it again I'd fix, like making sure I don't miss adding thickness in certain places. Also having a better form for the gallery. I admittedly botched this one together, but it did the job.

However, I have a bit of a problem that I definitely need help solving. With my form, I made a mistake on the gallery, instead of doing a hole for the flue that contains a recess that I can sit the vermiculite on to create a compressive layer for expansion and contraction of the flue, I just made a 9 inch hole. Worst comes to worst, I can probably put a form in there and stuff some mortar into it. and stick my flue in using david's method of installing flues. Please let me know any other suggestions or concerns that you may observe. Thanks.

[nuovopizzas]

Hey everyone. We’re 1 week and a day out from my intial cast. No cracks formed except for hairline around the joint. Success! I took off the front form for the gallery and I did find some mistakes that I could have prevented if I was more careful. I had my Buddy measuring where it was thick enough and I think he missed a spot. Anyways I don’t think it’s detrimental to the structure and I can put a facade on to cover it.

[nuovopizzas]

They are stainless according to the description on eBay. Will throw them in water and see what happens.

this was done on fiber glass and I haven’t remolded. I’m a little worried about moving such heavy, green concrete and not letting it cure properly. Plan to get it off the mold is to get some wedges beneath it and then get some guys to lift it up. I got a custom metal stand made by a welder so it’s going to go onto there. Will send pics when this happens.

[david s]

I shouldn't think the hairline cracks will be a worry. Stainless does rust but it's way slower so shouldn't be a problem. Leave some out in the weather and observe what happens to them. Are you 100% sure you have stainless?

Have you removed the sand? any voids on the inside should be filled in while the cast is moist and before it is fully cured.
How do you plan to move it onto the trailer?

[nuovopizzas]

48 hours after initial cast everything seems to be going well. No signs of major cracking just hairline at the joint between dome and gallery. One odd thing I noticed, which is shown in picture is rust coming from the stainless needles. I can’t imagine why this would be happening if they’re stainless steel

[nuovopizzas]

It’s all done! The whole thing was about 250 lbs silica sand 100 lbs Portland cement 50 lbs like and 30 lbs clay. Got a nice 2” inch thick layer around dome and maybe 1.5” gallery. I wrapped the whole thing in a drop cloth for painting and sealed all the edges to prevent moisture from escaping quickly. Im going to mist it a little for the next few days. Where I live it’s in the 100s for the next week so want to make sure it cures slowly.

Day after cast, I notice hairline cracks forming at joint between gallery and dome. What steps should I take?

[david s]

If cast in a mould, removed and replaced a 1" casting is vulnerable, but if cast in situ it won't be disturbed so I can't see you'll have any problems.

[nuovopizzas]

2% of ss needles and 2% of AR fibres by volume. Have you created a rebate in the gallery area so a door can fit against it nicely?

Yes I created a rebate in my mold for the door.

There aren't any problems with a 1" thick gallery correct? I feel like that was the generally accepted thickness for that area from the information that I gathered

[david s]

2% of ss needles and 2% of AR fibres by volume. Have you created a rebate in the gallery area so a door can fit against it nicely?

[nuovopizzas]

Tomorrow is the big day when I cast my inner dome.

I wanted to confirm a few details on the plan and see if there are any glaring oversights.

I will be doing a 3:1:1:0.5 homebrew consisting of 30 mesh silica sand (on the coarser side), portland cement, type S lime, and fireclay respectively. I have 2 lbs of AR fibers, 20 lbs of stainless steel needles, and 3 lbs of burnout fibers. I've heard you want to add the meltable extract fibers (AR+SS) at a 2% volume of your mix and the burnout fibers at 1%. Will the 2% by volume of AR + SS mean 1% each?

I am going to do a monolithic cast that spans the entire mold meaning the dome and flue will be one singular piece. The dome portion is going to be 2 inches thick and the gallery area will be 1 inch thick. I am going to use the kerosene/motor oil release agent combo recommended by David.

[nuovopizzas]

Luckily the distributor is only an hour and a half away so I’ll be making the drive to pick them up. It’s 60$ for a 55 lb bag. I am not extremely experienced with masonry and I don’t feel like going out and sourcing a bunch of different elements of the home brew mix. It’ll be easier to get the premix and not worry if I’m doing anything improperly. Thanks for your advice.