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johngalt 05-29-2010 07:24 PM

Utility Trailer Cast Oven Build
 
Well, after many years cooking pizzas, a few wonderful year with a cob oven outside, the brothers and I have decided to take the pizzas on the road. I've found so much helpful information here so I'll give back and document as much of the build as possible on in this thread.

Goal: A cast refractory concrete oven mounted on a standard 4x6 utility trailer. Trailer will be outfitted to comply with Colorado Health Regulations, including a sink with hot water heater (or oven-supplied hot water with pump, generator, and refrigerated prep rail.

I have the advantage of having an experienced welder/brother/partner in this endeavor, but If you want to do this, any decent trailer fabricator could provide you with the trailer built to spec.

Begin with:

4x8 utility trailer with 3500lb axle and 15" tires. Here in denver I can get one for about $1000.

The dome will be cast with a heavy castable refractory concrete, still working on the exact mix we can source here in denver. After speaking with a VERY helpful salesman at United Western Refractories here in Denver, and thinking it'd be good to go in and visit with the guys next week, as this is a very different project than their usual business. I got the feeling they'd be happy to chat and give suggestions.

I will be using the builds by MrG and JoeyValderain as models, thanks to both of you for posting your builds

I used Wolfram|Alpha—Computational Knowledge Engine to calculate the surface area of half a sphere with an outside-outside diameter of 44 inches, which would be an inside floor diameter of 40 inches.

using that, I come up with a surface area of 19.24 sq feet, and then using the concrete calculators http://www.concrete.com/calculators/concrete-materials-calculators i came up needing 4.6224 Cubic feet for the dome. Right now we're going to ignore the fact that it's going to have straight sides and also a cast opening. at 160 lbs per cubic feet, that's a weight of 739 for the dome, which is great...we're looking to keep everything under a ton, so looks like even with a slab under, and an entry way, we should be OK.

In all of this, I've been looking to keep my weight down and my oven size reasonable...I saw an Concessionaire model built by Into the Fire in Boulder, CO, and it was massive and looked VERY heavy. I want something more portable, pullable by small pickup, and not as expensive :-) Something you could fire up at home, then pull up onto a sidewalk and start slinging pizzas ASAP.

Oven floor:

I'm still in discussions with the health department, but am concerned that they may want to see a solid oven floor. state regulations state: "Multi purpose food contact surfaces shall be: smooth, free of breaks, open seams, cracks, chips, pits, and similar imperfections". I can't imagine a firebrick oven floor would get past that. Can you? Unless an oven isn't a multi purpose food contact surface? However, it looks like the Forno bravo oven that The Fire Within uses a forno bravo oven with a 4 piece floor, with BIG 1/2" cracks in between the tiles. I'd love to hear thoughts about this (it's not my concerns, it's Health Code)...if I can't use firebricks or a segmented floor, it will either be a cast floor, which will crack eventually anyway, or soapstone, which is going to cost $$$

Below the oven floor of 1.5 inches will be 2-4 inches of ceramic insulation board, and then ??? I'd like to avoid a slab of concrete because of weight. Could I use 2 sheets of 3/8 inch durarock cement board instead?

The oven will be supported in a cradle of angle iron, leaving us with storage space below.

Both MrG and JoeyValderain cast their ovens separately from the bases. Lacking an engine lift or forklift, I intend to build from the bottom up and pour the dome on the trailer.

For securing the oven dome to the trailer I'll have have bolts go from the angle iron cradle up through the insulation board and hearth, to be cast into the oven dome. I'd imagine we'd put nuts or something on the end of the bolts to give them more surface area to grip the concrete. I don't want this oven going anywhere.

I'll need hot water to a 90 degree temp. I could buy a propane hot water heater from an RV supply, but I'm going to be making my own heat whenever the unit is in operation. What do folks think about casting a copper pipe into the dome or hearth and pumping the water through? I'll have no way of moderating the water temp, barring mixing with cold, which would require 2 tanks...any thoughts on this?

That's where I am today. I'll post a few sketches and keep this updated as I talk with suppliers and the health dept on Tuesday. I'd invite comments and suggestions, and envy all of you who got to build your ovens without the Health department telling you what to do :)

If any of you engineers can design a silent, less than $700 oven-created-steam powered electrical generator to power my fridge I'm required to have on board (no ice for chilling ingredients), I'll send you a gift certificate to pizza hut.

Les 05-29-2010 09:12 PM

Re: Utility Trailer Cast Oven Build
 
John,

You may want to view the build of 100million as well. He just completed a very successful portable oven. I don't know the exact cost of his build, but I recall it being pretty reasonable. I'm sure he will be a good source of the good and bad.

Les...

david s 05-30-2010 12:03 AM

Re: Utility Trailer Cast Oven Build
 
When I built my mobile oven I made the flue removable so it would be less prone to wobbling around in transit. This has worked well and I would recommend it. I made a stainless steel sleeve which I set into the flue gallery and the flue pipe simply slides down into it.

skikvt 06-28-2010 06:43 AM

Re: Utility Trailer Cast Oven Build
 
How much does it weigh? We noticed the wheels on the upper base how do you move it? What is the diameter? Thanks

david s 06-28-2010 02:25 PM

Re: Utility Trailer Cast Oven Build
 
internal diam: 540mm
External diam: 900 mm
Weight : 170 kegs

factoryrat 07-31-2010 12:13 PM

Re: Utility Trailer Cast Oven Build
 
well any progress/pics, updates .....

brokencookie 07-31-2010 04:18 PM

Re: Utility Trailer Cast Oven Build
 
Quote:

Originally Posted by johngalt (Post 91019)

I'll need hot water to a 90 degree temp. I could buy a propane hot water heater from an RV supply, but I'm going to be making my own heat whenever the unit is in operation. What do folks think about casting a copper pipe into the dome or hearth and pumping the water through? I'll have no way of moderating the water temp, barring mixing with cold, which would require 2 tanks...any thoughts on this?

I just went thru this process with the Dept of Health and Dept of Ag in Washington. So your regulations may vary. However, they will probably not buy off on using the oven for hot water. They need to see a consistent temperature over time and the route you are suggesting will probably not do that. My health dept requires a 105 degree F for 5 minutes. The difference might be the purpose of the sink. I have 7 sinks in my trailer, the dishwashing etc sinks are @ 105. I bought an on demand water heater. A $300 investment that takes care of all my needs. With less sinks you can probably get a smaller one for around $200 out the door.
Tankage
Again, regulations vary. However, I was required to have seperate water and waste tanks. The waste tank had to be 1/3 bigger than my water tank and had to have an overflow alarm. I also had to certify and document where I would be dumping my waste.
In my experience the health dept is not your friend and they are not there to help you. I call them the dept of NO.


Hope this helps

Bruce

PedaroniCachini 10-01-2010 11:26 AM

Re: Utility Trailer Cast Oven Build
 
Hi there,

your thread sounds amazingly like the situation I am in now. Im setting up a mobile pizza trailer and I am about to start building the oven but there is a few things i need to find out and clarify before i start building.

Did you find an alternative to the concrete floor under the ceramic board? anything lighter. everything is so heavy!

Is there any way of making the oven less likely to get cracks during transportation from bumps in the road, i.e silicone instead of mortar in between the cast oven and the oven floor? Or does it just hold up?

Your project really interests me because it feels like just what i am going through at the moment. I hope yours is going well. Thanks, Simon

johngalt 10-02-2010 07:33 PM

Re: Utility Trailer Cast Oven Build
 
So far, so great. Our oven was finished on August 1, and has been hot and cooking at least 5 days a week since then. AMAZING! Over 1000 pounds of flour have been turned into pies and my partners and I are astounded at the reception we get. We know we're successful when the italian bistro down the street calls the police to check our "license" to be sure we're save (we're licensed, stayed, and I'm sure we cooked more pizza that night than they did)

So on to your questions:

we used 3/8 plywood, then a concrete board called durrock (it's a fiberglass mesh/cement board made for ceramic tile underlayment) Those layers were simply glued together with a construction adhesive. Then we go to 3 inches of ceramic insulation. That was pricey. But we cast our oven directly on the insulation, and I think overtime that will compress a bit and will be a better surface for the oven than something rigid. I think that 3 inches was overkill. 2 inches would probably be fine. Our base goes like this, from bottom up

tubular steel frame - Plywood, durrock, 3 inches of ceramic fiber insulation board, fireclay-sand mix (1inch for additional thermal mass) - 1 1/4 inch soapstone as hearth.

I would HIGHLY suggest finding soapstone, it makes a wonderful cooking surface, and have seen other ovens (cough cough) that are supplied with a hearth that has giant 1/4 -1/2 inch spaces in the seams. Not what I want to be dealing with as I cook 5-6 pizzas in the oven and try to move them around the zones.

We cut the soapstone with a diamond blade that we bought and put in a standard circular saw...$50 bucks for the blade and make sure you have a really good respirator.

The plywood is never warm to the touch.

The oven floor is set inside the oven walls...we set it inside the form before we poured the dome, so there's not 1000 lbs of concrete riding on our soapstone hearth. I'm sure it would crack with that weight on it.

Feel free to PM me with detailed questions of any sort. I'm happy to help.

I may be coming to London over Christmas...get cracking so I can come have some pizza when I'm in the UK!

Tman1 10-06-2010 03:42 PM

Re: Utility Trailer Cast Oven Build
 
Some pics would be nice... :D

How much do you think you saved? I suppose I should ask how much time went in to building it?


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