Build Your Own $20 Outdoor Cob Oven for Great Bread and Pizza

by ziggy on September 12, 2009 -- 58 comments -- Follow

Improved Cob Oven DesignCob Oven Update! (1/26/2015): This $20 cob oven article has been the most popular entry on my website since I originally posted it. It’s been 5 years since I wrote it, and we’ve made significant improvements to the original design, resulting in a much better outdoor pizza oven.

I highly recommend reading the Better Outdoor Pizza Oven Plans if you’re interested in building one of these for yourself. The instructions there are much more detailed, too. Here’s the original article for posterity…

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I must admit, I’m a bit of a breadhead. Few things are as exciting to me as freshly baked bread with a dab of butter, or hot and greasy scallion pancakes, or fluffy and airy naan, or a pizza fresh from the hearth of a wood-fired cob oven. (That last one trumps all the others.) I thrive on bread. I love eating it, and of course I love making and baking it, too.

cob pizza ovenEarlier in the year, the idea of baking in the outdoors in a wood-fired oven became something of a romanticized (in every positive sense of the word) notion to me. It was soon obvious that I should build a cob oven, which would be fairly easy and quick to build, and quite cheap, too. Compared to masonry ovens, which can cost hundreds or thousands of dollars and usually require pretty intense materials in their construction, a cob oven can be made from very simple, locally available materials. (Although it must be said that masonry ovens undoubtedly have a longer lifespan!)

So I picked up a copy of Kiko Denzer’s Build Your Own Earth Oven, a little gem of a book covering the construction of cob ovens from the ground up. And in July, after I settled into my new house, I knew it was time to start building this oven I had been dreaming about, so I could finally make pizza the way it was meant to be baked: on a super hot brick hearth.

How To Build an Outdoor Pizza Oven

Outdoor Pizza Oven FoundationThe Foundation

With little more than some clay, sand, sawdust, brick, some recycled beer bottles and old cinder blocks, I had everything I needed to make my own oven. After familiarizing myself with Kiko’s design, I began building the foundation for my version from the reclaimed cinder blocks and a few chunks of urbanite. A foundation raises the oven off of the ground and places it at a more convenient working height. (A hearth 40″ off the ground is a good average working height.)

The Fire Brick Oven Hearth

An insulating layer of beer bottles in a sawdust/clay mortar was assembled on top of the foundation in a ring of cob and beneath the firebrick hearth. The hearth, a simple arrangement of 17 recycled firebricks, would serve as the bottom of the cob oven, where breads and pizzas would bake directly. The hearth bricks were carefully laid on a thin bed of sand, so that they could be gently tapped to be firm and level.

Outdoor Pizza Oven Hearth Insulation Outdoor Pizza Oven Hearth Insulation 2
(Laying out the beer bottles, and later, filling in with sawdust/clay mortar)

Sizing the Cob Oven

I chose to construct a 22.5″ diameter oven, deciding that anything bigger would be beyond my current needs, and after using it, it’s definitely proven to be the perfect size. You can fit three medium-sized loaves of bread, or one or two small personal-sized pizzas in it at once. And at this small size, the entire mass can be heated to about 700 degrees in two hours of solid firing with good wood.

Making a Brick Arch Doorway and Cob Dome

Before building the actual dome, I made an arched doorway with some reclaimed red brick, mortared with a sand/clay mix. (The doorway is a little narrow at 12 inches wide, but so far everything I’ve wanted to fit has slid right in. And it can’t make really big pizzas, but I’m liking the smaller sized pies.) The cob dome (nothing more than a mix of sand and clay at a 3:1 ratio) was carefully built up around a moist sand form covered with wet newspaper and up against the brick arch. The sand was piled out of the doorway after the dome had dried a bit.

coboven-08form.jpg coboven-10arch
(Tracing the brick arch to make a cardboard form, setting the bricks on the cardboard form)

coboven-12mortar coboven-15sandform
(Finishing touches on the clay/sand mortar between bricks, then making a smooth sand form)

coboven-16cob coboven-18pileout
(Four inches of cob go up around the sand form, and later, the sand is dug out out the dome [interior view])

One more note about the door: the door is a critical 63% of the cob dome height, or 10″ high. (The dome is 16″ high, which is Kiko’s recommendation for cob ovens across the board.) This one measurement is the most critical because it allows the oven to actually draw. You see, the door is left open while the oven is firing, so that cool air is drawn in, and hot air and smoke can pass out the top half of the door. (Larger ovens frequently have a chimney, or you can make a simple firing door to help with draw, too.)

Cob Dome Insulation and Plaster

A several inch thick (between 2″-4″) layer of insulation (a mix of sawdust and clay slip) went over the whole dome. This layer helps to keep the heat longer, allowing for longer heat and longer bakes. Cob ovens built strictly for pizza don’t require such a layer, and more serious bread bakers may want to double up on insulation thickness, since it will allow for the baking of many loaves. Finally, a thick layer of earthen plaster covers and protects the whole thing.

build your own pizza oven cob pizza oven
(2-4 inches of sawdust/clay insulation is built up, and next is the nearly finished product with earth plaster and a door)

That is pretty much the whole oven. Pretty simple, huh? Kiko’s book is a fantastic resource for how to build your own, and I highly recommend it. I didn’t work on the oven very inconsistently (due to weather, etc.), but I imagine it took less than a week of actual construction between April and I. (And much of the time is spent waiting for things to dry, too.)

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Baking Pizza in Your New Outdoor Oven

There is nothing quite like wood-fired bread and pizza. Feeding the oven with wood, and watching the fire burn is an awesome experience. When the draw is just right, you can hear a low rumbling of the burning wood within the dome, which is rather powerful.

Other than being stupendous for baking tasty food, the oven is a great example of a simple technology that isn’t dependent on fossil fuels for its building or use. You need only simple natural and recycled materials for its construction, and wood to keep it baking. Getting away from cooking with propane is certainly in my realm of interests, and the oven has proven itself to be an important piece of that goal. I hope to have another cob oven more integrated into our subcommunity’s full-on kitchen once it is under construction. This oven encompasses many of my loves: baking, cob, wood energy, and the DIY philosophy. Not only that, it cost less than $20. (The firebricks were the only significant cost at $1 each.)

If you have any interest in baking, especially baking really damn tasty bread and pizza, or baking without propane or other fossil fuels, check out Kiko Denzer’s Build Your Own Earth Oven for complete details and how you can get started! I cannot recommend it enough.

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  • Jacques

    Great stuff. Can’t wait to have my own 🙂
    Here’s a suggestion for you: cover the foundation of the oven, it will look more natural 🙂

    Again good job!

  • roboslob

    wtf is cob?

  • Derek

    How will this stand against the weather?

  • Derek: Not that well with just an earthen plaster – right now I’ve just stated to build a roof to protect it, so I could be rid of the ugly tarps that cover it now.

  • Selina

    Will your food have a smokey taste?

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  • Perry Post

    Awesome. Did firing it too early cause the cracks, before it was fully dried? How long was your dry-time before firing? Did it patch up good as new or have the cracks been an ongoing issue?

    Thank you for sharing!

  • inc

    In Mexico, these ovens are/were popular to my knowledge. My grandpa built one in the yard, when I lived in Mexico City. My relatives used it to cook meat for tacos, bread, etc. It was yummy!

  • Perry: I don’t think firing it too early caused cracking, I think it would have happened no matter what. I’m not sure how to avoid it, really. I actually fired it to help it dry out.

    I patched the cracks up some but they are still present – they kinda open up as the oven gets hot, and close a bit when it cools…

  • That’s friggin’ cool. I bow to your oven producing skills- and maybe, just, maybe I’ll attempt this, although our climate is pretty severe. Thanks for sharing this and keep us updated!

  • Matt Arnold

    Where do you put the food that is to be baked, without putting it in the fire?

  • amy

    I hope you aren’t encouraging people to do this in California, the air pollution and PM from your wood burning stove is bad for you. You’re better off with cleaner burning propane, and so is the environment.

  • ziggy

    Matt: The coals are removed and the hearth swept clean (once the fire dies down), and the food is then baked directly on the brick hearth.

    Amy: What about the process to actually make that propane in the first place? Isn’t that extremely toxic and polluting itself? I imagine there’s a lot more energy (and pollution) that goes into extracting oil from the earth and refining it than using scrap lumber and dead wood.

  • John

    You are indeed putting a massive amount of PM10 into the air with scrap lumber in your unbaffled, noncatalytic wood oven; about the same as a dozen diesel buses idling outside your door. Even more if you’re burning unseasoned wood.

    Take a look at aerial pictures of Haiti to see what happens when too many people decide to burn wood instead of denser, cleaner fuels. Pizza looks good though.

  • Amy seriously, how much pollution could this cause? Propane is clean, but isn’t renewable. Ziggy, we need to build a solar pizza oven next.

  • Uncle B

    I would as an ardent environmentalist, rather see, a Fresnel lens or great parabola style heat source – as is done in India. This “Perpetual” of renewable (synonymous) resource give off no CO2, no noxious hydrocarbons, and makes for a sterile and toxin free cooking space where food flavors are not influenced by outside agents. Suppose the heat retention of the Cob to be much greater than conventional electric ovens, this same oven electric powered could prove to be of great economy even if electric powered! There is and enormous insulating gain here! Lets really exploit all facets of it – not stop at wood burning for fuel!

  • Okay, so I want to make one of these!!! but question: let me get this stratight: where does the coals go? you light it how? the how do you put food in? all help appreciated!!!

  • noah

    Yeah, there’s a reason people moved away from wood. I love the taste of wood-fired bread, but wood is much worse for the environment than almost any other alternative. Not to mention that wood-cooking is infeasible for any large number of people.

    It’s also not clear to me how you reconcile “i don’t like cement” with “old cinderblocks”. The concept of “urbanite” is pretty damn funny to me, too!

  • candace – You build the fire in the oven and burn it for up to two hours (depending on what you are baking/cooking). After it gets up to temperature, you scoop out the coals, and sweep the hearth clean, and bake directly on the hearth.

    noah – Sure, of course there is a reason people stopped cooking with wood, but I don’t think it’s quite that simple. I think wood-fired cooking makes plenty of sense if you are cooking for groups of people, and not for just yourself or a couple other people. And by the way, every time we fire the oven we’re baking multiple loaves of bread (2-3), at least a dozen small pizzas, a large pot of beans, and pie or cookies or some other baked good. Oftentimes we dry herbs at the very end, too. So we’re making food for multiple meals, and for 5-6 people.

    I would not fire this oven unless it were to bake/make a significant amount of food.

    I absolutely don’t like concrete, new concrete, anyway. It’s got a huge amount of embodied energy, the manufacturing process is polluting and toxic, and the stuff doesn’t go away. I’m completely fine with recycled or reclaimed concrete – I mean, where else is the stuff going to go except sit in big yards or on the side of the road? Why not reuse it?

  • Burning wood in a stove or oven releases no more pollution or toxins than letting the tree rot in the forest… so I see no problems using wood to heat my house, warm my water and cook my food. Of course, I live in the middle of a forest, not a densely populated city, so the small amount of smoke produced by my non-catalytic high-efficiency woodstove (you just need an afterburn, not a catalytic – that’s another misintereptation of data), and my wood-fired smokehouse and outdoor oven really isn’t hurting anything or anyone. Plus, wood is freely available and renewable, so I don’t have to travel anywhere or go through any extraordinary processing… just cut down a tree, buck up some stove lengths, split it and let it dry out.

    Very cool cob oven! We had to make ours a little bigger so we could fit our dutch oven through the door, but it was worth the extra effort. We also had to add 3 layers of insulation, with the middle one being a vermiculite blend, since we use our oven for bread and roasts even in the winter when it’s -40 degrees out! With only one insulating layer, there is no way we’d be able to keep the heat in long enough to dry a tissue, much less bake anything 😀

    One adaptation that I think I will add to my next oven is the also add a hot box in the pedestal under the firebricks so that I can put the coals in there once removing them from the fired oven and that should help keep the oven hot enough just a little while longer.

  • awesome! seems easy but i bet it’s really hard.

  • mlaiuppa

    Actually, those cracks can be avoided.

    You have to let your oven cure longer and slower before firing it.

    There are quite a few websites with details on building a pizza oven outdoors. I’ve considered it but don’t have the space.

  • James

    Ziggy – Nice work. I’ve been needing to upgrade my outdoor oven and you’ve got some good ideas here that I intend to incorporate.

    Jennine – good thoughts on getting more mileage out of the coals. I bake and grill a lot with wood and as soon as the food comes off the grill or out of the oven I shovel the leftover hot coals into a metal trashcan with a fairly tight fitting lid. The oxygen is used up and the fire is snuffed within minutes. And then I have a quick starting set of coals for my next cooking event. And less labor cutting wood.

  • Bruce in Italy

    That is exactly how the Italians built the fondos (basements) and stalla (stalls) that are under almost all the many century old Italian homes. The brick work was done on a sand/earth form and then emptied out afterwards. The groin vaulted ceilings are fantastic works of art and they are as strong today as they were then.

  • Here’s link to the one we built. One more layer left to do.

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  • Montanabay

    why do you need the bottles for insulation? Don’t you want the whole mass to heat evenly to retain maximum/consistent heat?

    just to be clear, the bottles layer is filled in with cob, then a thin layer of sand over that to help level the firing bricks, which end up being the cooking surface?

  • The bottles insulate the bottom of the hearth, so your firebricks don’t lose heat as quickly.

    The bottle layer is filled with a clay/sawdust mix, which is different than cob – it’s more insulative. There is a small amount of cob over these bottles, and then yes, sand and the bricks.

  • Zack

    Thanks for this great stuff. A dozen diesel buses, huh? Unbelievable.

    I was just wondering where you got all this stuff from? I have the empty beer bottles, I also homebrew (wonder if the green police drink wine or beer, because we know which one is more sustainable), but I am wondering about where you got the other stuff and where you would recommend looking for it.

  • The clay: from the ground. The sand: from a leftover pile from building projects. The red bricks: from an old demolished building. Firebricks? Bought used from friends. Sawdust? Free from a mill. Cinder blocks: well… can’t remember exactly where, some were from a friend, some came from elsewhere.

    I would recommend looking for some of these things (brick, concrete) at old building or demolition sites, road deconstruction sites (concrete)… Sand? Maybe from a nearby river, or again, a building site or you could probably buy a bag or two… Sawdust? Maybe from your city’s recycling yard or local mill. Firebricks are hard to get used, you might have to buy those.

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  • Daniel

    LOL! I really get a kick out of idiots that carry their environmentalist diatribes too far. Makes me very glad indeed that i dont live anywhere near california!
    I bbq quite often and sometimes up to 8-10 hours to cook a brisket on a wood fire. I hope my smoke travels in the atmosphere and sinks in california somewhere!

    Thanks for the ideas Ziggy! I cant wait ta get started on my cob oven!

  • JosephTree

    Ziggy, lovely presentation! My good friend and I fired up our new oven and baked bread for the first time today. The first 3 loaves came out beautifully brown and utterly tasty in 16 minutes. we roasted dinner and cooked veg form the garden in subsequent batches. We too used Kiko’s 22 1/2″ model. We will be building a shed roof to prolong the oven’s useful life, but otherwise we’re oven twins! Hooray!

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  • John McCrossan

    Hi All:
    I do not share the enthusiasm for this relic of the fossil fuel age. The same week our air quality in Vancouver Canada tanked at “6” (highly dangerous)because of the forest fires to the east, one of these smoke-belching anachronisms started burning happily at a nearby community farm. No emission controls required, thank you very much.

    Smoke from all wood-burning sources is highly toxic because wood combustion produces compounds that are poisonous to our human physiology. Wood smoke causes asthma and deadly lung diseases and adds to the greenhouse gases overloading our biosphere.
    We have 10 per cent of the population in Cnada suffering from asthma and other serious lung disease, that means in British Columbia alone over 200,000 people are afflicted— family, neighbours, work colleagues.
    This is a pivotal period in our history when we need to eliminate all unnecessary combustion to reduce pollution.
    I support all government agencies in all countries who have to regulate residents to stop using OUR air as a dump for wood smoke. Each and every woodfired Cob Oven is one CO too many.

    Just to respond to some wacky comments above: (1) “burning wood equals same emissions as letting it rot” – pollution dangers are all about exposure levels, spreading the rot over ten years keeps the exposure levels down.
    (2) “Toxins” – please do your homework if you want to have your comments taken seriously: “toxins” come from living things, poisons come from dead things (3) Daniel – you are a sick man, literally. Better get these lungs checked out, you are spending way too much time breathing in carcinogens that emanate in the wood smoke. And stay away from California, its too nice a place for people who want to injure others.

    Ziggy – Pleeeeze use a solar panel and be truly green and earthy.

    reagrds all, John The Canuck

  • Vicki Morell

    Dear Ziggy and all,

    Before you go ahead and recommend these cob ovens, what studies have been done to prove that they are safe and they don’t produce particulate matter or any other dangerous emissions? I would love to read your studies please. Thanks.

  • Giulia

    I am Italian and My father and I had built a real out door oven…I had fun building
    the oven with my Dad and the food tasted good but it takes hours before you can bake in it and the smoke was over whelming that the nieghbours complained…long story short we have not used our out door oven for over 20 years, and it still stands outside our backyard at our country home…looks good though.

  • Ernest Grolimund

    Free energy? That is what gets them started. Stove, boiler, firepit, barbeque. The burner stands clear of the smoke, enjoys all the benefits, and smokes out all his neighbors, who come to hate it because it makes them sick. $2,700/burner/year in various health costs to the victims and society according to gov studies on stoves. Not exactly free huh?

    Natural? Yeah, like hell. Jesus recommended making chappatis and cooking them in the sun on some kind of black stone or metal surface that can get up to 140 degrees on a sunny day. Sprout the wheat to get rid of the gluten and makes chappatis or pitta bread and you have something good that does not smoke out your neighbors by using fiery furnaces.

    I had a free energy kind of guy living next to me who put a neighbor in a hospital from a heart attack and caused an asthma atack in my daughter. If it happens again, I will take him to court with a doctor, lawyer and witness standing by me. Then we will see how cheap it is. This could all be avoided with a little proverbial wisdom and understanding. Judges say when there are clean alternative forms of energy available they must be used.

    Burning wood like this is 500 times worse for global warming and causes health destroying air pollution. Propane, electricity from wind or geothermal or tides or hydro or solar or other sources much better. Buy bread from someone who knows what he is doing.

  • Janey

    Regarding the statement:
    “Feeding the oven with wood and watching it burn is an awsome experience.” Do you know what else is an awsome experience – trying to breathe with 30% lung function when the air is full of wood smoke. Now that is a truly awsome experience – you should try it some time.
    I would suggest you use propane or solar power but please do not burn wood. What gives you the right to pollute the air I breathe with your smoke? If you can keep your smoke on your own property – by all means go ahead and burn all you like. But when your smoke comes onto my property and into my house, then you have a problem. – me! The person in the middle of the forest is the only one who should be using something like this – where the smoke does not go onto another’s property nor into their lungs.

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    Do you have any recipies for this kind of oven? Or maybe cooking in a fireplace?

  • Travis T


    Great post! Question about the ceiling… “The cob dome (nothing more than a mix of sand and clay at a 3:1 ratio) was carefully built up around a moist sand form covered with wet newspaper”

    OK, so the ceiling is simply sand and clay. Have you had any problems with dirt falling into the food? If you touch the ceiling does anything fall into your hand?

    I found that my local library has Kiko’s book! I’m going to get it right away.

  • Travis: Nope, I haven’t had any problems with grit in food. I have never bothered to actually touch the ceiling, so I’m not sure.

    Tania: Well, just about anything you’d make in a regular oven could be cooked in this style of oven. (But it will taste better in this kind, winkwink.) Cooking over a fireplace is very different than cooking in this oven…

  • benny R

    ever tree hugger in the world would find something wrong with anything you do unless it was there idea, most are sick and want to tell everyone how smart they think they are there is a nut on every tree, they are the ones that fell off

  • chris

    Nice oven, a fire box would be a good addition, but with a shoestring budget you did very well… I plan to build one of similar construction.. just as a large outdoor cooking area… a pizza oven with firebox and smoker/bbq grill.. I like the simplicity involved with your design.. Some people here forget their propane, solar, electric, oil, or cow poo’d powered item… is built over seas and sent here.. MANY PEOPLE can find clay and sand in their back yard.. and all other items are mostly locally found items.. half dont even require addition packaging… so about toxins and whatever some people are crying about… would you rather huff all the stuff from the manufacturing process of your purchased product, stryrafoam, smelting metals, mining… now compare this 20$ oven too your 300 $ oven or 1k-2k pv array.. and consider ever dollar you earn how much fuel or gas do you burn… driving to work… and the total habitat destroyed for everything involved in the process.. yet alone in this throw away society when his oven needs repair is 95% clay and sand.. when your oven needs repair… your replacement parts and more packaging are floating over the ocean… and to the canadian about the forest fires.. when oil was being burned of the surface of the ocean before it made land fall on the gulf coast it was 50 miles of coastline being hit with fumes… but that wasnt a natural environmental process was it..

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