Make Pizza With a Plasma Cutter, a Backhoe and a Pile of Mud!

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Introduction: Make Pizza With a Plasma Cutter, a Backhoe and a Pile of Mud!

About: Fritz Bogott live in woods, write with pen, cook with fire.

After several years of baking in North House Folk School's wood-fired brick oven, I decided to build an oven of my own. I went a little crazy with extra features (slab foundation, arches, ash dump, chimney, doors, wood storage) and decorations (limestone around the foundation), but you can make a very usable version in a weekend with salvaged materials and a couple of friends.

The place to start is Kiko Denzer's "Build Your Own Earth Oven".

I also made extensive use of Daniel Wing and Alan Scott's "The Bread Builders", which is a great resource even if you're baking bread in a regular electric oven.

Step 1: Bushwhacking, Lumberjacking and Limestoning

We have a big lawn next to the neighboring farmer's field, with a great view of Carleton College's wind turbine. What a great place for a pizza party!

The most obvious place to put the oven was in line with our garden shed, but the whole area was a dense jungle. I spent a day with our Stihl brushcutter, with a saw blade in place of the string trimmer. That thing would be awesome for fighting zombies!

I had to chainsaw out a medium-sized box elder tree as well.

Under all that jungle, I discovered an improbable trove of cut limestone left over from when they built our house in 1973. Too good! I'll use that for the keystone and the stone veneer around the foundation.

Step 2: Screeding, Floating, Edging and Brooming

I decided to start with a concrete slab foundation.

My brother-in-law spent the spring of 2007 building park structures and sidewalks with the Gulf Coast Community Design Studio in Biloxi, Mississippi, so he was fresh on all the aspects of concrete work.

Step 3: Stacking, Pinning and Filling

The North House oven has wood storage and an ash dump underneath it.

I wanted to emulate that, so I built a three-sided box out of dry-stacked cinderblocks, and my dad and I filled the four corners with concrete and rebar.

Step 4: Boxing and Dumping

I built a fireproof box out of cement board held together with angle iron and bolts.

Cement board isn't very strong, so my friend Chris kindly welded me a steel frame to span the cinderblocks underneath the cement board.

The inner box is the liner for the ash dump: It's a hole for the coals to fall through when I sweep out the oven. I will set a small grill under the hole to catch the coals.

Step 5: Hoeing and Heaving

Oh, crap! I'm building a clay oven, but our whole yard is sitting on fifteen feet of the world's best topsoil. There's no clay in there anywhere.

Chris came to the rescue once again. He used his backhoe to dig a bunch of clay-and-sand subsoil out of a hillside on his property, loaded it into a giant plastic bin on the bed of his truck, and drove it to my place. Ever tried to lever a seven-hundred-pound bin out of the bed of a giant diesel truck? Chris has.

Step 6: Chipping, Thieving, Mixing, Setting

Now that I've got my subsoil, I can fill the cement board box with insulation: glass bottles set in a mud-and-wood-chip matrix. (Chips don't hold or transmit heat, and they eventually burn out, leaving voids that also insulate.)

I made a bunch of wood chips, but the chipper threw its belt and started on fire. That was the tool gods telling me I had enough chips. Hmm, now for an instructable about replacing the belt on a chipper.

The night before recycling day, I drove all over town and stole everybody's glass bottles.

Then I tried to put it all together, but I kept running out of bottles and having to go out for more. Officer?

I left a four-inch-deep rectangular void in the center. The thermal mass will go there.

Step 7: Leveling and Laying

I poured buckets full of thick mud into the void above the bottles, and screeded the whole mess with a big 2x4.

I let the mud dry partially, and then my daughter and I set firebricks in the mud. These firebricks are the hearth-- the actual baking surface. The mud beneath the bricks holds heat from the fire. The bottles beneath the mud keep the heat from leaking out.

Step 8: Arching

I went over to Chris and Tina's, and we laid bricks on the floor in arch-shapes. We laid out two arches: One smaller rowlock arch to frame the inner door and one larger soldier arch to frame the outer door.

Tina took photos of the arches, and then traced the outline of the inside of the arches in Adobe Illustrator. Chris plotted the outlines on his big plotter, taped the plots to masonite, and bandsawed the masonite.

I took the masonite and stapled it to some short sections of 2x4, making one masonite-2x4-masonite sandwich for each arch. At this point I had two arch forms.

I set an arch forms on chopsticks on the hearth and balanced bricks on the forms. Then I took a deep breath and yanked the chopsticks. The form dropped and the arch settled but did not fall. I pushed the form out and filled the gaps in the arch bricks with mud.

Hey presto!

Step 9: Castling

We built a sandcastle the shape of the oven void. Negative space!

We'll dig the sand out through the door when the oven is completely built and dried.

Step 10: Mudballing

We covered the sandcastle with a layer of damp newspaper as a separation layer.

Then I mixed up a power of mud by doing the mud dance.

Then I stacked mud balls all around the sandcastle, smooshing each one against the ones below.

This layer is the oven dome, which holds heat and radiates it down from above.

Step 11: Popcornballing

Having no more wood chips, I made the next insulation layer out of mud mixed with vermiculite. Had exactly the texture of popcorn balls.

I stacked popcorn balls all around the oven dome, smooshing each ball down as before.

Step 12: Adobeing

I made mud-straw ropes and used them to build a tunnel connecting the inner and outer arches. The straw made each rope velcro to the next. They didn't need to be supported from below!

I left a five-and-a-half inch gap in the top of the tunnel, took a six-inch-diameter stovepipe and wodged it into the gap, straightened the pipe by eye from the front and the sides, then built up more mud-straw ropes around the reasonably-plumb pipe. There's nothing keeping it up there but friction.

Then I covered the entire oven with mud-straw mix, for protection and final shape.

You can't believe how well mud and straw holds its shape. If you've ever built free-form shapes out of clay, working with adobe will feel like antigravity magic.

Step 13: Slamming

Tina called me up one morning to say they had some vacant space on a steel panel on its way to the CNC plasma cutter, and would I like anything cut?

Well yeah, oven doors!

Chris took the arch drawings, smoothed and enlarged them, and had them cut out of heavy-gauge steel. He added flanges and handles, and I insulated the inner door with plaster of paris mixed with vermiculite.

Thanks, man. Nice doors!

Step 14: Veneering

I dry-stacked limestone blocks around the front and sides of the oven, just for looks.

The blocks across the top of the hollow space are held up by a couple of bolted-in L-brackets. I'm surprised they hold, but they were the simplest thing that could possibly work.

Step 15: Baking

I have to fire the oven for about two hours to get it up to temp: I fire it until the soot burns off the ceiling, then for about another half an hour, and then it's hot enough for pizza-- somewhere above 800 degrees. I push the coals off to the side with a weed-whip, then mop the exposed floor with a damp rag wrapped around the weed-whip. Then we're ready to bake.

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    84 Comments

    user

    That looks awsome, have you ever concidered using a rocket stove design for the heat source? Based on what I have read it is suposed to burn cleaner and use less fuel.

    1 reply

    Well, this build isn't easily modifiable to efficient combustion. I built it *because* it's technology from the middle ages.

    But for sure, it's pretty much the worst way of turning wood into heat. A rocket oven would be a much better way to do it, if you aren't hung up (as I was) on a particular historical design.

    My dad has a little table-top Uuni rocket-stove pellet-burning pizza oven, which is *very* fuel-efficient! http://uuni.net/

    I'm very interested in making one of these this coming summer and will be drafting my own design over the winter at college. Very nice ible, by the way.

    My questions for you:
    What did you encounter during your building that you think would be good for first timers to know? (I plan on getting Kiko's book)

    How long did this take, from first breaking terra firma to cooked pizza?

    2 replies

    If pizza is what you want, then 4" of thermal
    mass is WAY too much. An inch would be more like it (though you'll have to use your judgment anout fragility vs thickness. 4" takes FOREVER to heat.

    Building the foundation, block frame, steel frame and arches took all the time. If you build Denzer's basic version instead it will go together like magic. I wanted the fancy extra options, but they took 80% of the effort.

    But the main things I'd have done differently are less thermal mass and a permanent weatherproof roof. Tarps shred and blow loose all the time.

    Great to know, thank you Mr.Bogott!
    I've been doing some drafting in google sketch up. I was planning on making it under a lean-to on the side of our barn, good deal of shelter.

    Hello Fritz, Wonderful instructions. About the foundation - did you go below the frost layer, or is that simply a pad? Thanks.

    3 replies

    Sorry - I see that you poured a slab. Have you been through a winter yet? I'm wondering how it's holding up.

    It's just a pad, on about a foot of gravel. Definitely not best-practice. We figured that the consequences of a big ol' crack through the concrete pad just weren't severe enough to justify the effort of a properly-built foundation. If the base were mortared or if the oven were brick we would have made a different calculation. But we've been through two Minnesota winters with it and it looks like new.

    I am wondering if concrete pavers instead of a slab over the bed of gravel that you descibed would be the easiest way to go and not have to worry about cracks

    Made my own earth oven!!! After several re-readings of your proyect, I finally made it! I work in a proyect located in southern Veracruz, México, and we are fortunate enough to have clay everywhere... (www.losamigos.com.mx).

    I want to post the memories about the construction I wrote on our blog.

    http://estampaverde.blogspot.com/2010/04/fiat-panis-o-de-como-hacer-un-horno-de.html

    Its in spanish, but anyways... I might try the wood door because there isn't any metal workers around!!! Any advice on baking??? How long shall I leave the oven to dry before starting a big fire???

    1 reply

    Hi Antonio,

    (Pardon my English.  I speak German and Chinese but very little Spanish, even though I could use Spanish every day in my own town if I had more time to put toward it...)

    That oven is beautiful!

    I don't know how long to let it try.  Mine is cracked on the inside but is still holding together.  I don't know whether it would have cracked less if I had let it try more???

    Certainly the first couple of firings will eat a LOT of fuel as the fire burns out the remaining moisture.  You'll want to start three or four hours before you cook.  Once the dome dries out it will take more like 90 minutes.

    When you first start the fire, the oven ceiling will turn black from smoke.  It will stay black until the dome surface temperature hits around 530DegC.  Then the smoke will burn off and you will see clean clay.  In my oven (which I built too thick, I think) I keep firing for about 30 minutes after the clay burns clean.

    When I bake pizza, I leave all the coals in the oven and just push them to one side.  You may need to keep feeding skinny sticks onto the coals so you get some radiant heat from the flames to brown the top of the pizzas.

    If I'm baking other things, I shovel the coals out, mop the floor, and then use the 'ouch' test to test temperature.

    At pizza temperature (375-475DegC), I can't put my hand into the oven at all.

    At bread-baking/meat and fish roasting temperature, I can count to three until I have to jerk my hand out.

    Much longer than three and the oven is colder than I use for much of anything except beans and stews.

    Ask me more questions any time. I love to talk about baking!

    -Fritz

    fritz-what would you say to topping off my adobe bread/pizza oven with clay brick and a mortar mix w/perilite? the oven works nicely as is but to make it more wisconsin weather-proof- i don't want to make a shelter for it because of where it is located nor keep a tarp over it except for winter weather-i've been thinking about it and i can't see any reason that it would disturb the tempertures-i would really like your opinion on this thought-bev

    1 reply

    Hmm.  You don't want to wrap adobe in anything waterproof without an air gap, because then the steam inside the oven will condense on the waterproof layer and turn the adobe back into mud.  That's what's going on with those A-frame roofs-- oven, then space for air to flow around the oven, then a waterproof roof.  As long as there's an air gap, you're fine.  I don't know whether that automatically breaks your "no shelter" requirement?

    very nice i might make one for my self

    Greetings.  I have questions if you do not mind.  First, if, like me, metal work is not going to be practical, what would you suggest the doors be made out of?

    Second, I was wondering if you thought of using the bottom area as a bbq smoker, with a tad of alteration I suppose

    Kevin
    Buffalo, NY

    3 replies

    Hi Kevin,

    The Denzer book (which you should buy because it's great) suggests making a door out of adobe or wood.  You may need to soak a wooden door in water for a few hours before using it so it doesn't scorch too badly and so it contributes some steam.  Anything would work though, really.  A stone or concrete paver if it's not too heavy?

    As far as metalwork goes: I usually find that the most fun part of any project is hunting around my county for people who know the trades I'm missing and hiring/befriending them.  You meet new people and learn a lot, and it expands your sense of what you and your growing crew can build next time.

    You can totally use the oven as a barbecue pit.  Just keep a slow fire going off to one side and throw some soaked chips on the fire from time to time.

    It's fashionable among molecular gastronomes and Make Magazine readers to use a computer-controlled blower to keep the pit's internal temperature as stable as possible.  <a href="http://www.mikezed.com/">Mikezed</a>, whom I met at Maker Faire SF 2008, encouraged me to try that with a cob oven.  I haven't gotten around to it, but perhaps you could pave the way?

    -Fritz

    Thanks so much.  That temperature controlled blower sounds good, but I like things as simple as possible.  Living in a similar climate as you, I am concerned with having to cover the oven with a tarp, but I suppose a protective wood structure around it after it is built might be neat, especially as you say if it is designed to allow moisture to leave

    time to mix up some more clay and perlite! fritz thanks so much for your help

    fritz: my mudd was cracked so badly i ended up taking it apart and starting over with new mudd yesterday-well i have it covered with plastic and it's doing some cracking close to 24 hrs later-question for you: how long after you did the mudd balling did you start the second layer of insulation? p.s. send good clay!!!!