48" Mobile Oven Build

[nuovopizzas]

Hey Forno Bravo Forums,

I have been lurking on this forum for a couple of years now. Last year I did a backyard 40" Pompeii-style refractory cast build, so I am slightly familiar with the process.

To explain the situation a little bit, I just graduated college and want to start a small business. After building my 40" oven, I put a lot of time into learning how to make good Neapolitan pizza; go figure. Now I want to open a food truck in my hometown (population of around of almost 500,000) that only has one restaurant that offers true Neapolitan pizza. I see an opening in the market.

Anyways, I am looking to build a 48" cast build on an enclosed trailer to make this business plan possible; I need this size so that I can keep production up. I have done research on this forum about builds similar to what I am trying to do, but wanted to run some ideas past the forum, and I will keep the forum updated with my progress and what I learn during this process.

I am casting my dome using a mold I made using fiberglass and a 48" medicine ball. I want to do a one-piece cast, I have heard this is good for damage prevention when on a trailer. I have the means of moving it onto the trailer with a forklift so weight is not a problem.

Next, I want to cast the gallery as well, where I will make a form to cast the gallery. The details and technique I will use to do this is to be determined, I still need to do some reearch and experimentation on how I can execute this properly. This is once again done for the sake of being on a trailer, I do not want mortar joints that are going to "crumbe to bits" as the infamous David would say.

The mix I will be using is a homebrew of fire clay, Portland cement, vermiculite, and sand with silica. What I want to add to the homebrew is either stainless steel needles for reinforcement or basalt fibers I have heard is the new thing to add.

Most of my questions are about the base of the oven, however. Something I need to take into account is weight, I want to minimize weight as much as possible without losing out on oven performance. The way I thought I could do this was by reducing the depth and size of my hearth, but I am not quite sure how the decrease in thermal mass would affect performance. The dome would be about 2 inches thick of refractory cement and then 3 inches of thermal blanket. I would use medium-duty firebricks for the floor and 2 inches of CaSi board beneath. Beneath that, I plan on having the 2-inch hearth. Does anyone foresee problems with this?

Lastly, for the stand, I plan on creating some sort of steel structure to put the heart on. This is something I am not familiar with as well because, in my previous build, I used cinderblocks for the base. But obviously the weight of that is immense.

Any input is greatly appreciated and if anything needs to be explained or drawn out, I can do that. Just trying to get a post out to get the ball rolling.

Thank you everyone for creating such a good resource, without you guys I would have never came across this passion of mine.

[david s]

A few observations and tips: First up I’m not quite sure how you plan to make a 48” oven from your 42” fibreglass mould.
I’ve always believed that two smaller ovens on a trailer are a better option because it’s much more flexible in terms of output, fuel usage (of both the oven and the vehicle to haul it) and floor recharging. Two operators that have such set ups that I’ve spoken to heartily agree.
You should also calculate the weight as the springs on the trailer or vehicle that take the oven need to be matched to the load. Calculate the volume of a sphere ( outer radius and subtract the volume of the inner sphere (inner radius) then divide by 2 as it’s a hemisphere. Add in the weight of the supporting slab, insulation and outer shell, flue and door.
The thinner you make the casting the weaker it becomes.
I have basalt fibres, but the ones I bought have a variety of fibre size and on mixing tend to clump, making even dispersion more difficult than AR glass fibres which are larger and far easier to mix in. Both are expensive, but around the same price.
A custom made stainless gallery is a good option for a mobile oven due to its weight saving.

[nuovopizzas]

A few observations and tips: First up I’m not quite sure how you plan to make a 48” oven from your 42” fibreglass mould.

I have already made the 48" mold. I have a friend who is very experienced with fiberglass help me out with this.

I’ve always believed that two smaller ovens on a trailer are a better option because it’s much more flexible in terms of output, fuel usage (of both the oven and the vehicle to haul it) and floor recharging.

Because this is an enclosed trailer this seems difficult to do... due to size constraints and also seems to be generally heavier. It is a 24' x 8' trailer. This would also make me have to install 2 vent hoods, 2 fire suppressant systems, and for safety regulations, the ovens have to be bolted down so it's not like one oven could be rolled off?? if I am understanding that correctly.

Thank you for the other input I will keep this in mind. The weight limit of the trailer is 7,000 pounds so I feel like I am good in that regard, but its something I need to stay on top of.

Where could I find a custom stainless gallery? I have not heard about this.

[david s]

My mobile oven rolls on and off my trailer on a wheeled trolly. but the mobile oven operators I mentioned both had their ovens permanently mounted on their trailers. If trade looked like being slow then only one oven was kept up to pizza temps. as well as smaller functions being economically catered for.
The stainless flue gallery can be done in a number of ways. Here's one that I recently built, although it's only the top section, the whole gallery including entry can be stainless. Any sheet metal shop would be able to manufacture it.

[nuovopizzas]

My mobile oven rolls on and off my trailer on a wheeled trolly. but the mobile oven operators I mentioned both had their ovens permanently mounted on their trailers. If trade looked like being slow then only one oven was kept up to pizza temps. as well as smaller functions being economically catered for.
The stainless flue gallery can be done in a number of ways. Here's one that I recently built, although it's only the top section, the whole gallery including entry can be stainless. Any sheet metal shop would be able to manufacture it.

The stainless steel gallery is definitely something I will look into... what type of insulation would I put around it? Just the normal fire blanket with refractory cement exterior?

[Karangi Dude]

This is how I built my mobile oven

Check the build out at: https://community.fornobravo.com/for...-s-mobile-oven

Cheers Doug

[Ronstarch]

nuovopizzas would you mind sharing some details and photos of how you built the fiberglass mold for your current build?

[nuovopizzas]

nuovopizzas would you mind sharing some details and photos of how you built the fiberglass mold for your current build?

Yes I will take pictures and explain how I make the mold. I am remaking because I got the dimensions off, will update you shortly.

[david s]

Not too sure about your proposed mix, are you using a tried and proven mix recipe? You haven’t included proportions, but the strength of any mix is dramatically reduced if it includes vermiculite. In addition it makes the mix insulating rather than conductive. Also as Portland cement begins to deteriorate above 300C the strength of the casting could be further compromised. Hydrated lime in addition to Portland cement is an important ingredient in the mix, to take over as the cementious material should the Portland cement fail.

A 48” oven will be really heavy, usually a 4” supporting slab is recommended for most ovens with larger ones requiring perhaps more. However you do what you can get away with, but heavy brittle materials are vulnerable to travel.

2” of calcium silicate under floor insulation is also considered minimal.

[nuovopizzas]

nuovopizzas would you mind sharing some details and photos of how you built the fiberglass mold for your current build?

Hey, I just finished my dome mold, I simply used epoxy, hardener, and fiberglass to cover a 48" medicine ball inflated into a hole cut into a table. I did 3 layers to make it very firm and support the weight of the concrete cast. Attached are images of the fiberglassed ball.


https://gyazo.com/cc8f92a8050dcc598462e101f87a3f91

[nuovopizzas]

Not too sure about your proposed mix, are you using a tried and proven mix recipe? You haven’t included proportions, but the strength of any mix is dramatically reduced if it includes vermiculite. In addition it makes the mix insulating rather than conductive. Also as Portland cement begins to deteriorate above 300C the strength of the casting could be further compromised. Hydrated lime in addition to Portland cement is an important ingredient in the mix, to take over as the cementious material should the Portland cement fail.

A 48” oven will be really heavy, usually a 4” supporting slab is recommended for most ovens with larger ones requiring perhaps more. However you do what you can get away with, but heavy brittle materials are vulnerable to travel.

2” of calcium silicate underfloor insulation is also considered minimal.

I am using the 3:1:1:1 mix with burn-out fibers and stainless steel reinforcing needles. If you have a recommendation for the amount of burn-out fibers and SS needles to include in % of total brew that would be extremely helpful. I saw something like 3%. I also saw you use AR fibers/basalt fibers. Can't find too much info on that so might just add the SS and burn out and call it a day unless I find some more solid info on the other two. In my previous cast build I did not use hydrated lime, I used Portland cement and vermiculite. What are your alternative suggestions? I have looked through many threads and haven't seen an advised homebrew mix that includes all these separate "ingredients" in one.

Lastly, I am going to use 4" of Casi board and a 4-inch concrete slab beneath. Because this is a mobile oven I am going to custom manufacture a steel stand for it to sit on. The logistics of this stand are going to be worked out with a friend who is an engineer. Will update the forums with the info I find out. I am going to use a steel curb that is larger than the diameter of the oven as a means of locking everything in. The void will be filled with vermicrete most likely. Also, I am going to cast the dome and gallery separately as I have seen you have advised this in previous builds.

[Ronstarch]

Hey, I just finished my dome mold, I simply used epoxy, hardener, and fiberglass to cover a 48" medicine ball inflated into a hole cut into a table. I did 3 layers to make it very firm and support the weight of the concrete cast. Attached are images of the fiberglassed ball.


https://gyazo.com/cc8f92a8050dcc598462e101f87a3f91

Thanks for the reply. So that will be your inner mold, and you’ll have no outer mold, is that right?

[nuovopizzas]

Thanks for the reply. So that will be your inner mold, and you’ll have no outer mold, is that right?

That is correct. You can see in the back, a preliminary mold for the gallery as well. I will do about a 2" thick layer of refractory cement on top of this.

In my previous build, I added fins going perpendicular to each other to split the cast into 4 parts making it easier for transportation. But for the sake of my mobile build, I have heard that a dome with no joints is stronger.

Creating the fiberglass mold is as easy laying the piece of fiberglass cloth onto the ball, stretching it to take out any wrinkles, then pouring the epoxy/hardener mixture onto it, and using a plastic paint scraper to spread it around, saturating the blanket. Let me know if you have any other questions.

[david s]

The recommended addition for ss needles is 2% by volume and for the very fine pp fibres 1%
The homebrew recipe is 3:1:1:1 sand, powdered clay, hydrated lime, Portland cement.
However, because this mix contains a very high proportion of clay there is considerable shrinkage that can lead to shrinkage cracks. Clay additions for mortars are recommended to be no more than 7% by volume. Halving the clay content in homebrew puts it at 8% rather than 16%. This does reduce its stickiness, but still allows good workability. For both use as a mortar and as a castable I halve the clay content. There have been no reports of problems when used as a castable over a sand dome, but this is probably because there is a little give in the sand mould. If using a fibreglass mould there will be no give which could create problems for you. I’m not 100% sure of this because I use a proprietary castable refractory which has 0 shrinkage.
The other problem with using a fibreglass mould is that you will have to remould the casting and then relocate it into position, using a sand mould allows casting in situ and simply removing the sand from the inside.

[nuovopizzas]

The recommended addition for ss needles is 2% by volume and for the very fine pp fibres 1%
The homebrew recipe is 3:1:1:1 sand, powdered clay, hydrated lime, Portland cement.
However, because this mix contains a very high proportion of clay there is considerable shrinkage that can lead to shrinkage cracks. Clay additions for mortars are recommended to be no more than 7% by volume. Halving the clay content in homebrew puts it at 8% rather than 16%. This does reduce its stickiness, but still allows good workability. For both use as a mortar and as a castable I halve the clay content. There have been no reports of problems when used as a castable over a sand dome, but this is probably because there is a little give in the sand mould. If using a fibreglass mould there will be no give which could create problems for you. I’m not 100% sure of this because I use a proprietary castable refractory which has 0 shrinkage.
The other problem with using a fibreglass mould is that you will have to remould the casting and then relocate it into position, using a sand mould allows casting in situ and simply removing the sand from the inside.

Okay, interesting. I did not use hydrated lime in my other build and have had no problems. When you say clay, I am assuming you are referring to fireclay. I also used vermiculite in my other mix. I am assuming you say not to add this because it weakens the cast. It will be on a trailer so it is something I have to consider. The greatest benefit is that it makes the dome much lighter which is nice, but again at the cost of strength is something I do not want to do.

If I am interpreting what you are saying correctly, you half the amount of clay you use. Making it more like a 6:1:2:2 mix respectively. There actually is probably a slight amount of give in the fiber glass mold so hopefully the shrinkage won't cause problems, if it does I will let you know.

I have not come up with a plan yet to get my mold out from under the dome. In my last build I built it in four pieces to it was easy to just peel back each piece one by one, but I have access to a forklift so I think that will help me out in some shape or form.

What amount of burnout fibers should I be using?