baking expert seeks oven expert. MHGSOH!!

[michaelthebaker]

hi everyone, finally got round to registering after many times reading very interesting threads. i don't do forums, apart from dan lepards excellent baking forum, so i'm a real novice and technophobe. but i've been baking professionally for over 30 years, following in the footsteps of father and grandfather, so i consider myself to be a very knowledgable bread baker. i am retired, only 45- baking is a hard life, and for the past few years have been building clay bread ovens at fesivals, gatherings etc, a real hippy- so my friends say. i call myself a sacred baker.

well my new project is to build a concrete pizza oven on a trailer to tow behind my home- a converted mercedes bus- yes really! i have done lots of research, seen the veraci pizza site and links. but i still have a number of questions, some very specific, but it seems you lot are the most knowldgeable anywhere so here goes.

the veraci pizza oven is supposedly adobe, correct? looks like some cement to me, as if adobe surely it would shake to pieces on the trailer.

using refractory cement should i strengthen it with steel, mesh, wire.

the weak point i think is where the oven shell connects with the hearth, any ideas on stopping breakage here.

the trailer is gonna be a 2nd hand caravan chassis. i believe the oven and hearth will weigh less than a ton. any ideas on suspension and stopping it all falling to pieces.

i look forward to hearing from you all, and thank you in advance. i dont often have net access living in the bus so i apologise if my repsonses take a few days, i am not ignoring you, just awol in the woods.

i will of course be posting on going pictures and stories, when i learn how to download pics and upload onto the net

hope that you all achieve everything you aim for in 2008. best wishes

michaelthebaker

[Dutchoven]

Re: baking expert seeks oven expert. MHGSOH!!

Welcome to the forum!
Hmmm! Have to think about this one a bit! My opinion on the reinforcement is Yes! Will you only be making bread or will you be doing pizza also?
Dutch

[michaelthebaker]

pizza, bread and cakes

hi dutch. want to be able to bake many things, so need quite alot of mass in the hearth and oven walls to to bread and longer cake baking and meat roasting when oven iscooler. getting trailer with 1.5ton rating so my calculations on cement density/volume indicate i can have hearth 6-8inches, including vermiculite, and walls 5-7inches thick. strength is my main concern, as i dont want to see my livelihood fall to pieces behind me as i am driving down the road.

all comments much appreciated

HOME IS WHERE THE HEARTH IS

[n2iko]

Re: baking expert seeks oven expert. MHGSOH!!

Vermiculite concrete might not be the better choice here, look into the ISOL type bricks. There is going to be a lot of vibrations even when the trailer is sprung well.


--mr.jim

[Dutchoven]

Re: baking expert seeks oven expert. MHGSOH!!

I agree with mr.jim...I think insulating firebrick would be a better choice for the trailer application as the vermicrete that I have seen stays quite flaky...I think they are also a bit lighter in weight although with a trailer rated for the load you speak of that is not a worry...I might suggest an Alan Scott type oven if that is not already what you were thinking of...using that type you might create a steel harness around the upper walls before cladding and then insualating...the bounciness of the trailer might have a greater effect these since that is where the thrust of the dome enters the walls
Self taught hearth bakers is what we are...what experience do you have with Pumpernickel? Have made attempts at it and the flavors were spot on but made some errors in technique and got frankenstein loaves.
Will continue to share my thoughts on your project!
Best
Dutch

[Acoma]

Re: baking expert seeks oven expert. MHGSOH!!

You may be better of with some type of plate assembly oven than brick due to roads and vibrations. Your brick and mortar may hold for a few travels if all went well, but you would not want to be at some gathering, show up, and have unstable bricks cracking everywhere. FB has modular ovens that to me, seem best for such travels. Also, call their 800 number, ask for their engineer, and see if it would work.
You could also call this company that does portable oven parties.

two

[cvdukes]

Re: baking expert seeks oven expert. MHGSOH!!

A fully wire-reinforced concrete stucture shell can take an a lot of vibration. For case in point, look at how ferro-cement boats can take pounding seas where other boats break up.

Also, to minimize vibrations, get away from the idea of using standard leaf springs and shocks on the trailer. Springs between the axle and wheels are okay, but for minimal vibrations, you'll want to extend the sides of the trailer up above the level of the hearth floor and basically suspend the oven with paired shock absorbers at each corner. Countweights and damper systems can help if you get them right, otherwise they could cause greater oscillation.

[michaelthebaker]

Re: baking expert seeks oven expert. MHGSOH!!

thanks for all your suggestions. going to see some mechanical design friends this weekend for a design blitz, will put all your ideas in the mix and see what arises.

PROOF IS IN THE PUDDING

[dmun]

Re: baking expert seeks oven expert. MHGSOH!!

I'm a little concerned about the re-inforced concrete idea. Regular mesh/re-bar re-inforcement isn't used with refractory concrete because of the large temperature variations in ovens: the big difference in co-efficients of expansion between the masonry and steel can set up stresses and cause cracking and failure. Cast refractory is re-inforced with stainless steel needles.

Someone correct me if I'm wrong, but I don't think anyone here has built an entire dome out of refractory concrete, except for Ed Schmidt's geodesic. We've seen plugs for the top of the dome, and flue funnels. Would these withstand bouncing around? Refractory concretes aren't as strong as portland cement based concretes.

Once you start springing for castable refractories, and stainless needles, you're talking about serious money just in materials. It may pay to look at the pre-cast modular ovens, that have been successfully used in mobile catering ovens. They are much stronger, and less prone to cracking in ordinary service.

[CanuckJim]

Re: baking expert seeks oven expert. MHGSOH!!

Michael,

Have a look at this site: http://www.thefirewithin.biz/Home.html. Joseph uses FB modulars for his portable ovens.

Jim

[n2iko]

Re: baking expert seeks oven expert. MHGSOH!!

Another idea, if you build the dome/iso/hearth inside of a pan like structure you might be able to use air bags to dampen the vibrations. Deflate the bags to use the oven and pump it back up to travel.


--mr.jim

[michaelthebaker]

Re: baking expert seeks oven expert. MHGSOH!!

thanks for all the positive advice. will be speaking to forno bravo about a precast oven but they are in segments and i wonder hwo they would perform on a trailer. we will see. i would really prefer to build my own. anyone one know about these silica fibres or stainless steel needles that could be added to the cement to give it strength. i'll continue with the planning stage. later.

[edschmidt]

Re: baking expert seeks oven expert. MHGSOH!!

I just checked the castable refractory which I used and it has a modulus of rupture of 2000psi. With one caviat, it must be brought to 2950degF to reach this strength. Even at 2500deg. the modulus is only 500psi. What is the modulus of normal concrete?

[cvdukes]

Re: baking expert seeks oven expert. MHGSOH!!

>>I'm a little concerned about the re-inforced concrete idea. Regular mesh/re-bar re-inforcement isn't used with refractory concrete because of the large temperature variations in ovens: the big difference in co-efficients of expansion between the masonry and steel can set up stresses and cause cracking and failure. Cast refractory is re-inforced with stainless steel needles.<<

When I mentioned ferro-concrete...I was not thinking of refractroy cement and stainless steel.... My experience is strictly with normal ferro-cement made with standard hog-wire fencing, chicken wire and masonary topping mix cement. Maybe I got lucky when I made my pizza oven this way but I've fired it up to full temp at least 10 times now and haven't had any indication of cracking anywhere in the dome. Last weekend, we ran 14 pizzas through it during an oyster roast party. I could have cooked several more, but everyone was full from the oysters too. Thats on top of our temps swinging widely... had a low of 16 F the day before the party. Normally I'm at cooking temp in an hour of firing but it also took longer last weekend because all my firewood was wet when I started and I was more occupied stoking the oyster fire.
I've rechecked my construction costs and now think that I have a total of $63in materials in the actual pizza oven dome. Since cost is an issue, I would sure try to replicate my success with your mobile oven. Figure the worst you'll be out of is less than $100 if it doesnt work, but I pretty sure it could take the vibrations of a mobile oven.
Just to repeat how I did the pizza oven (see my post on newbie intros)...the shell was 3 layers of 1 inch mesh chicken wire over hog wire fencing (picked up off rubbish pile at no cost), hand-packed with topping mix and kept moist during a week long cure. After that, handpacked unfired stoneware clay inside the dome...couple of days of air-drying during which the clay cracked something fierce. So covered clay with layer of fiberglas reinforced concrete Then since I didnt want fiberglass fibers flaking off into my food, I did a thin layer of portland-fireclay-sand-powdered kaolin.
My oven floor was a single pour of the portland-sand-fireclay-kaolin mix to about a 3 inch depth. Now I do have slight crack in it because it has no reinforcement and probably did not cure long enough before I starting firing the oven...but nothing major.

[dmun]

Re: baking expert seeks oven expert. MHGSOH!!

This is interesting to know. Our refractory ovens are way overspec for our under 1000f temperatures. Ceramics people build kilns exactly like ours (firebrick with refractory mortar, wool and cal-sil refractory insulations) in similar thicknesses, and regularly fire them up to orange heat.

The pompeii plans have long said that you could use plain red brick if that's all you could get. Folks in Australia where fire brick is expensive and hard to get have built such ovens successfully.

If a plain concrete dome with chicken wire reinforcement will work fine, it's good news for our builders on tight budgets. I found that the insulation was more costly than the dome materials, so I don't know if it's that much of a overall saving.

This is just me, don't beat me up or anything, but I think a brick oven should be made out of brick. I love sliding a pizza onto that herring bone pattern floor.