If you can’t find an answer to your question here, in the book, or elsewhere on the site, please feel free to leave a question in the comment section and I’ll get back to you asap (if you scan the comments, you may well find your answer there).
I’m delighted to hear from you and to help; please do write/ask questions! Please be patient, as I have a lot of irons in the fire. Do let me know if you need or want an extended conversation.
Jump to: Efficiency, design, etc. | Using the oven | Materials & Construction | Foundations | Mud vs. Brick Efficiency, design, etc.
Q: How efficient are earthen ovens? A: There are three things to consider here. First, since you have to heat up the whole mass of a retained heat oven in order to bake, clearly, cooking just a few loaves of bread won’t make efficient use of all your fuel. However, the more you cook, the more of the stored heat you use up, and the better your efficiency. Insulating an oven increases efficiency even more, as does using it again before it cools off (daily use, of course, is best). Alan Scott told me that one baker he knew cooked 630 pounds of dough with the heat from 130 pounds of wood (the oven was hot from the previous day). That was sixteen and a half bakes from a single firing! Better than 250 two pound loaves! That’s almost 5 pounds of dough baked per pound of wood burnt — pretty good! Second, smoke is unburnt fuel, so a smoky fire is not efficient. If your oven is already hot, it will burn cleaner because the masonry won’t be sucking heat out of the fire so fast. (see the upside down fire.) There are, also, many designs for wood-fired ovens. Some burn much cleaner and more efficiently than a cold earthen or masonry oven. However, you can make your mud-oven burn cleaner by using the driest wood; starting with a small fire, building it up slowly, and insulating. If you only want to bake a couple of loaves, you can build a rocket oven, like Flip and John’s. Or a Barrel Oven. (Also see the next question. If you want a super efficient, clean fire and a retained heat oven, (and you live in a cold climate) you may want to build a traditional masonry heater, such as those described in The Book of Masonry Stoves. (See Resources, and the chapter on fire, p. 93.) Third, there are efficiencies that don’t reduce to numbers so easily. Consider, for example, the efficiency of buying a brand new Prius so you burn less gas on your way to your hi-tech job to earn money to buy organic produce from a farmer far away that you cook in your brand-new, super-efficient electric oven. Is that more efficient than buying an old pickup to haul materials so you can build an oven, grow a big garden, run a home-based business, and have bread to give to your neighbors? Sometimes, learning to burn wood to cook your own food also teaches how to make do with what you’ve got, how to work with other people, how to build other things that will further improve and/or simplify your life, and how to shrink your needs and desires. Which is the “most efficient”? I think that’s a choice worth thinking about — and defending!
Q: I’m looking to build indoor masonry heater type units out of earth for heating and cooking. Any ideas? A: Ianto Evans and Leslie Jackson’s Rocket Mass Heaters covers rocket stove design for indoor heating and heat storage; Ernie and Erica Wisner’s website offers courses or you can buy their Rocket Mass Heater Guide book. Aprovecho Research Center publishes “Capturing Heat,” volumes1 & 2, that include designs both for efficient cookstoves and ovens. The Masonry Heater Association website has a wealth of resources. The Rocket Stove Experimenter’s corner is a community of tinkerers and rocket scientists. “Answers Questioned.”
Q: Is there any effective difference between the Quebec shape and the beehive shape? A: The major feature of the Quebec oven is a longer, egg-like shape. It’s useful if you need a wide door (for pizzas or cookie trays) but don’t want to hugely increase the diameter of your oven, or if you bake in square pans and want a longer shape with corners. The long oven can accommodate a wider door without giving up too much thermal mass. Some say it’s more efficient, but I haven’t seen any experiments that have proved it either way. That said, it’s good to keep the dome 16 inches or less; more volume reduces the concentration of steam which also inhibits crust development — in addition, increasing the distance between loaves and hot mass reduces the intensity of radiant heat.
Q: Have you experimented with electric heating elements? A: One reader wrote that he had tried a 3000 watt range element in an oven made of refractory cement. He said it never got up to temperature, even after 8 hours. A nichrome kiln element might provide more heat. And, like a kiln, I imagine it would be good to place the element in a channel, to increase surface area and contact between the element and the oven material. But that’s going to get complicated. Also consider that (in all cases except hydro- or solar power) electricity requires burning fuel to generate electricity to generate heat again — wasting large amounts of energy at every step — a very inefficient way to bake. I met a commercial baker who switched to propane when he got tired of splitting wood for his brick oven. But he said wood gave him a “deeper heat” — longer lasting and more effective.
Q: Is it better to build my oven with or without a chimney? A: When I first wrote the book I thought chimneys made better ovens because they made a faster, hotter fire. I even built a cross-draft oven with a chimney in back which burned great, but used LOTS more wood. It also illustrated a basic fact that I understood, but didn’t quite accept; that is, no matter where you put it, a chimney sucks heat out of the fire. After years of observing slow fires licking the walls of the oven, I now think the traditional oven with no chimney is probably best because heat transfer is a function of “the 3 Ts”: time, temperature, and turbulence. A slower burn gives the oven mass more time to absorb the heat of the fire. However, if smoke is going to cause problems for you, or if you just need to control it, then yes, build a chimney by all means.
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Q: I built a small oven that burns OK to start with, but no matter how I play with the fuel, it gets very smokey and goes out. The door is 63% of the interior height of the oven, so what am I doing wrong? A: Since the cut of the doorway will tend to angle down, the inside edge of your door may be lower than the outside edge. So be sure to measure door height at the edge furthest inside the oven. Be careful not to add too much fuel at once, as this reduces the space for oxygen to mix and move in the oven, which will makes for a smokey fire. (See p. 100) If your door is the right height, you’ve played with the fire, and the oven still won’t burn, try cutting the door a bit higher, or making a hole through the back of the oven (opposite the door, just above floor level, and at least as big as a quarter. Plug it up with mud or a stick when you bake.) Both provide more oxygen for combustion. And finally, the biggest combustion problems tend to be in the smallest ovens (again, the smaller your oven, the less room for fire. Try using smaller wood, a little at a time, tend it closely, and and let it burn longer.
Q: Do you find that cleaning the oven causes damage? A: I’m pretty careful to keep the hard edges of my scuffle and peel away from the oven walls. It is harder, sometimes, to be so careful when tossing wood into a raging fire—but not impossible. I have noticed that ovens with a metal door support, or a pre-fabricated door and frame, tend to crumble where mud meets metal. Of course, hot metal expands more than hot clay. However, it doesn’t seem to impair overall oven effectiveness. Perhaps the greater risk is thermal shock, which can crack floor bricks and generally weaken oven materials. Reduce thermal stress by avoiding the use of water, either for steaming bread or for cleaning (or cooling) a hot oven floor. If you’re being careful with your tools and still having problems with interior oven damage, it may be that your original mix is weak—silty, sandy, or made w/too little clay. Rebuilding the oven may be your best solution.
Q: The snap-swivel on my scuffle keeps breaking — help! A: I had the same problem, so I made a stronger swivel by wrapping a turn of stiff wire loosely around the end of a cotter pin or the end of a nail. The other end of the wire holds my rag, and the cotter pin or nail is secured thru a hole in the end of my wooden handle. It works great.
Q: My nice wooden baking door is getting terribly charred. Do I just have to keep making new ones? A: I soak my door in a bucket of water while I’m firing the oven. That way it chars less, and adds a bit of steam. Also, charred wood actually lasts quite a long time, partly because it requires a higher temperature to ignite. So long as it has enough integrity to hold together, it should work.
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Q: I built an all-clay oven but it’s crumbly, and falling apart. It was definitely clay, not silt. What did I do wrong, and can I fix it? A: The mix may have been too dry, or not tamped hard enough, or both. Either would prevent the clay from cementing into a single, solid mass. Remember that it’s water that makes the clay stick together. If you dug your clay in the summer time, and it was dry, it can take a long time for it to fully hydrate. In fact, you might have to soak the clay for a couple of weeks, then let the wet clay dry out a bit before you build. You might be able to save it with an internal plaster (if you can reach—see safety note below), or by just brushing out the worst of the loose material—it still ought to work, if the floor bricks stay secure and the walls are thick enough.
Q: How do I know when it’s time to pull out the sand form? A: I find it easiest to build with a dry-ish mix (see p. 33-35). Then you can pull the form as soon as the first layer is done. However, if the first layer is soft enough that you can dent it with your finger, you should wait. Test the material again in a few days (or weeks, depending on weather and your mix). To let air circulate and aid drying, dig a narrow tunnel into the base of the form (if the sand collapses, stop!) When it seems ready, dig a shallow hole into the sand form to expose a fresh bit of the first layer. If it’s still soft enough to dent when poked, wait! If, when you do pull the sand form, part of the oven does collapse, stop, prop up anything that looks sketchy, and let things dry out. You may be able to patch it up with a sticky plaster (use lots of straw and clay). You may also need to poke sticks or nails into the hole to give the plaster something to hold onto. If it was a minor collapse, and your oven is pretty thick, it might not make any difference and you can just leave it.
SAFETY NOTE: If it’s a big oven, and you do apply an internal plaster, don’t put your arms and head in the oven without another person there to help in case of collapse. I’ve never heard of it happening, but I don’t want to.
Q: What’s a good plaster if humidity is a problem? A: If, by “humidity,” you mean moisture in the air, there’s nothing to worry about; neither lime nor mud plasters tend to soak up (unprecipitated) atmospheric moisture. Lime plaster is not necessarily “better” than plain mud, and both kinds of plaster still need a roof.
Q: Once the oven is complete, is it best to wait until after it’s been used for a bit before the finish plaster is applied? A: Earthen plasters don’t go through any chemical changes, so speed of drying has minimal effect—apply them when it suits you. If they don’t stick, spray the oven with water, or make a wetter mix. A good lime plaster, on the other hand, is best applied when the oven is still a bit moist. Lime plasters require water and time to effect the chemical reaction that makes them durable. Therefore, they are best kept damp (even covered) for a week or more. If you use lime plaster on a dry oven, soak it before you start. Best to use lime water (i.e., water that has had a bit of lime soaking in it to make it alkaline) to improve the bond. Lime is caustic—see cautionary note below.
Q: Is there a difference between mason’s lime and agricultural lime? Where can I get mason’s lime? A: Agricultural lime will NOT substitute for mason’s lime. Ag lime is powdered limestone, or calcium carbonate, (CaCO3). Farmers use it to make soil less acid. Mason’s, or “hydrated” lime, is limestone that has been cooked at very high heat (over 1500° F.), which drives off a carbon dioxide molecule (CO 2 ), to create CaO, or quicklime. With the addition of water, CaO turns to calcium hydroxide Ca(OH)2 . So lime plaster, when exposed to air, goes through a chemical reaction by which the soft calcium hydroxide exchanges a molecule of water (H2O) for one of carbon dioxide (CO2), and reverts to limestone. Any masonry supplier should have mason’s lime. Get it as fresh as possible, since, like cement, it “goes off,” or starts turning back to limestone if left to sit too long.
SAFETY NOTE: Mason’s lime is caustic: read the bag, and use gloves, goggles, and respirator as suggested. The best lime plaster is made by slaking quicklime into lime putty which, as long as it is wet, won’t turn back into limestone. But quicklime is hard to find, and slaking gives off immense heat; please do your homework, and be careful. See the Resources section in the book, and Lime in Building.
Q: Should I let the first layer dry before adding the next? A: It all depends. If you have limited time to work, sure, do it all at once. It may take longer to dry, but that’s OK. If you can do it in stages, by all means, let each layer dry out before starting the next. (But do finish the entire layer, because wet material doesn’t stick so well to dry material. And if you don’t let each layer dry out, the rate of drying will be slower—which can be a good thing, as quick drying can cause more cracking, especially if you’re building in the hot sun and one side gets more heat than the other).
Q: Should I fill any cracks before adding the next layer? A: If you’re building with a good sand-clay mix with minimal shrink (see p. 23), you shouldn’t have much, if any cracking. If, on the other hand, you’re building an all clay oven, the answer is a definite yes. Pure clay shrinks a lot—I’ve had cracks as big as a half an inch. If you let it dry completely, it’s easy to fill cracks from the outside before adding another layer.
Q: Would it be good to fire the first layer to harden it? A: Firing the first layer won’t make any difference to the second layer. If you take apart an old oven, you’ll see that only about the first inch of clay actually gets hot enough to harden (called “bisque” firing, the clay typically turns a lighter, often pinkish shade, and maintains integrity when wet).
Q: What about cracks? Should I worry about them? A: Probably not—cracks happen, but generally they’re not a problem. In general, any material that goes from 50-700°F and up in the course of a few hours is going to relieve the stress of thermal shock by cracking—more or less. The thicker the mass, the more likely the oven can absorb the stress without cracking. It may be that thicker material (and masonry of fired brick?) survives the stress of thermal shock by sustaining many micro-cracks, while thinner material sustains fewer, larger cracks. (See David Lyle’s Book of Masonry Stoves). Some cracking is simply due to the fact that materials expand with heat. I have seen at least one large masonry oven where the front hearth bricks had been pushed out a full half inch farther in front than on the sides! Some masons address that problem by building expansion joints into the masonry surrounding their fireboxes — i.e., they leave a piece of cardboard between firebox bricks and the rest of the masonry — when it burns out, it leaves a gap. Alan Scott used to hang the concrete floor slab on rebar and left a ¾ inch gap all around it — partly to keep heat from being conducted away from the slab, but also partly as an expansion joint. Cracks can be useful. Some bakers recognize baking temperatures by the width of their oven cracks. But cracking can cause problems too. They allow flammable soot and heat to escape from the oven, and the soot, or nearby flammables, can ignite. The Bread Builders talks about two bakers who barely missed severe fires, both partly due to oven cracks (p. 140). However, one of the operators was over-firing the oven, trying to get more out of it than it was designed for. And of course, fire is only a risk if flammables are too close to a hot oven. Some commercial ovens insulate with loose, non-flammable material, like perlite or vermiculite, on the assumption that it will fill cracks, and prevent the escape of heat and soot.
Q: I made a brick arch doorway and the center brick came loose — what did I do wrong? A: The bricks hold best if the inside corners are actually touching and if there’s a joint at the top center, rather than a brick. This allows the central wedge of mortar to serve as a “keystone.” If your door ends up with a brick in the center, make sure that the narrow end of the gap is a bit smaller than the brick. Then knock off just enough of the corners of the brick so that it will wedge into place, and make a keystone. If the gap is too wide, try turning the brick on edge, or orienting it longwise, and carving it into a keystone.
Q: I couldn’t find any pumice to insulate under the oven floor. I got vermiculite instead, but it seems too soft and squishy to support much weight_any suggestions? A: Compared to perlite and pumice, vermiculite is soft. If you use it under the floor of your oven, mix it with some clay slip (see p. 86) and let it set up hard before you build on it. As for pumice, another source might be a concrete block and/or brick manufacturer.
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Q: What’s the ideal height for a foundation? A: Well, there are several ways to answer that one. For someone who uses the oven a lot (at least once a week, every week — not just summer holidays), I’d say ideal height is to have the floor of the oven at the height of your waist. For someone who uses the oven less frequently, I’d say the ideal height is whatever is easiest to build. If that means you just want to plonk a ring of rocks on the ground, fill them with gravel, and go from there, that’s ideal. Remember, the oven itself is simple. The higher you go with the foundation, the more complicated it gets…unless you’re making a temporary oven, in which case a temporary foundation can be almost anything that will support the weight, and that can be protected from the heat of the oven fire.
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Mud vs. brick: Nine Arguments for Mud
- Dirt is cheap. And if you thought you had to have a brick oven, mud is a good way to practice. You can make mistakes and learn before you spend hundreds (or thousands) on bricks and a mason. Start small: a 21″ diameter floor area will bake several loaves, small pizzas, chickens, etc. and needs less wood and firing time. Our 31 by 23 inch home oven bakes a dozen 1.5 lbs loaves, and 3-4 hours of fire will bake two batches of bread, as well as casseroles, turkey, vegetables, soup, beans, etc. My biggest mud oven is at a restaurant: 4×4 foot on the inside; 9 foot diameter outside (see back pages for photo and story).
- Mud is brick. Fire turns the inside of a “mud” oven to brick (quality varies w/soil, clay content, your mix, etc.).
- Speed: I’ve built 12-inch diameter demo ovens in 15 minutes, and full-size ovens in half a day or less.
- Custom design; you can make a fast-firing, thin-walled pizza oven, a big oven for a home business, a sculpted outdoor kitchen with seating, and more.
- Sculptural freedom: you’re not limited to rigid, rectilinear brick forms (not that I dislike rectangles).
- Temporal freedom: built right on the ground, or on planks and sawhorses, a quick oven can serve for a day or a year.
- Carpenterial freedom: roofing not required: use a tarp (when the oven has cooled) or a piece of tin.
- Most important, your kids can do it with you _ especially good for young people who know more about computers than they do about the earth that gives them their food. Find out for yourselves how it feels to be a plant, with roots that can follow water down into the fertile soil, and leaves that eat sunlight. Perhaps that’s why mud feels so good between the toes (and dough between the fingers)!?
- Community: Just as the kitchen, or hearth, is the heart of a home, large communal ovens have long been the heart of communities. In the eighteenth century, after the Revolution that brought democracy to modern France, one of the first things the people did was to (re?) assert community control over the big ovens that had been under the regulation of feudal lords. According to Jerome Assire, in his Book of Bread,
In rural Europe, the various privileges [of the feudal system] included rights of banality over both mill and bakehouse, which were both the property of the suzerain. To bake their bread, the peasants were obliged to use these and these alone, and had to pay a duty to do so. People wanted to reclaim what was naturally theirs: the right to make their own food, and the right to join hands so that heavy tasks could be made lighter for all.
From what I’ve seen of ovens built by folks with whom I’ve been in touch since writing this book, ovens and community still go together — whether community is the family, the neighborhood, a co-housing group, or a town with a new restaurant. And it isn’t just the eating that joins us — it’s the joy of shared labor, which can be a novel and pleasant surprise in this industrial culture where people often work alone in offices and facilities far removed from sun, soil, and neighbors (as evidenced on the very last pages).
There are also, of course, numerous other places to see what folks are doing with cob. Here are a few to start with:
- Cob Ovens on Facebook
- The Rocket Stove Experimenters Page
- Dig your hands in the dirt! a blog about cob art all over
Hi Kiko,
Firstly, THAnk you so much for writing such an inspiring and awesome book ‘Build your own earth oven’!
It was my bible throughout the first lockdown here in the uk when i built my first oven (pics below) My two kids reveled in mixing cob with me! the neighbours said “your lucky we know you tony or, people would really wonder what on earth you are doing!”
I now have people wanting me to build for them and i am planning a course this summer.
We have starting building a base for a community initative https://www.wiveygrows.net/
Only thing is, the owners of the land are a little concerned about the idea of the oven. I am aiming to reassure them that, it is safer than a ground fire or BBq as it is contained and raised above ground. we would not leave it unattended at any time. They do have residents that still use the space but i will inform them that the heat left would be residual radiant heat enclosed in the oven which would be likely full of wood for the next burn.
Do you think there is anything ees i could add to reassure them?
oh, I can’t seem to load pics, how do i do this, thanks,
Tony
Hey, Tony, thanks for the lovely note. Good to see your site and learn a bit about all the good things you’re up to. Fire is a long conversation (especially when talking to someone in a state where 2020 wildfires killed 11 people, burned more than 1,000,000 acres (400,000 ha) of land, and destroyed thousands of homes). Here at my own home I think I’m extremely careful about tending my fires and minimizing fire risk, but a few summers ago, a freak wind caught a coal, blew it into an oven mitt that was (relatively safely) hanging nearby. The mitt caught fire, dropped to the ground, lit some errant kindling, and started burning the wooden leg of the oven roof structure. The oven was unattended for no more than 15 minutes, so the fire didn’t get very far, but mistakes and freak events can happen, and wind can do funny things — even if you clear all combustibles from anywhere near the oven. The risk is real. I can justify it on my own property, where I pay the insurance and will have to accept the consequences, but I don’t think it would be responsible of me to make any kind of recommendations for a situation I’m not directly involved in. That said, I have built ovens in public spaces, as have many others; they can provide enormous benefits in building community (look up “Cooking with Fire in Public Parks,” by Jutta Mason.) And of course, you and the landowners are the ones who will have to evaluate all the risks and decide whether the benefits outweigh them. Certainly if our ancestors hadn’t learned to manage fire all those many hundreds of thousands of years ago, we wouldn’t all be here now! Good luck, and let me know how it goes!
Hi Kiko – really enjoyed your book and built a covid-sanity-saving oven on wheels that I can store in my garage and roll into the driveway when in use. I built a wooden deck with 4 trailer jacks on each leg and two layers of wine bottle insulation, and a layer of copper pipes through the bottom layer that will get hot if the deck is in danger, which they haven’t so far. I learned a lot about going with the flow, a puttering about style of work, adjusting many many times as the unexpected occurs. Yields are a dozen or so 12″ pizzas in a firing, then a few loaves of bread, a pot of beans. It was and is lovely.
I’m writing about my next adventure and think a separate firing chamber below the main over would be fun and potentially useful for keeping the oven hotter longer. I’m adapting a design from your book on page 96 from Paul Mery. But I can’t tell if you meant for the separate firing chamber to maintain a fire while the pizzas are baking above or not. I thought it would be an efficient way of keeping everything hot, as the heat from the fire would keep the floor hot, as well as the upper surface of the oven for radient heat, and provide convection heat from the fire itself. Is this how you mean for the oven to be used, or the same way as the standard oven, heat and then remove the fire and seal up the exits?
Thanks!
Hey, Michael, got pix of the covid-sanity-saving-oven on wheels? I wanna see. (if you feel like sharing, please send ’em to handprint at cmug dot com)
As for the a separate firing chamber underneath, the best/simplest version I’ve seen is the one John and Flip Anderson did. Here’s their video: https://www.youtube.com/watch?v=uR-LqOquLZA&t=3s. But really, I suspect (for quality of pizza, at least), you’re not going to do better than the old traditional one, w/the fire in the chamber. You want the really high heat above and below. I haven’t cooked a pizza in Flip and Johns, but I seem to recall them saying their times were a bit slower than a typical wood-fired pizza oven. If you’re making a dedicated pizza oven, and not interested in bread at all, you can also improve efficiency by making the dome out of insulative material — or perhaps metal, covered w/insulation). Keep us posted, and good luck!
Thanks for the quick reply and link to Flip and John’s oven. As for photos of mine, I just realized I never got around to putting together all the photos. Here’s a link to my quick summary: https://cobpizzaovennc.blogspot.com/2021/10/building-cob-pizza-oven.html
Hello Kiko,
this summer I build a cob oven using your book as the plan. I think it turned out well. Your book was very helpful. thanks. I have several questions:
1. Is the out side of the oven supposed to get very hot?
2. My oven is the 221/2 size. iN Making a firing door, what would the door dimensions be? You made a door out of an old water heater. I am wondering the height, width and the distance out from the face of the oven. thanks for your help. Marty
Hey, Marty, thanks for the note; glad to hear your oven turned out well. Heat on the outside of your oven depends on three factors: 1) length and intensity of firing, 2) the thickness of your first (dense thermal) layer, and 3) insulation. Insulation is most important. W/out it, there’s nothing to slow down heat transfer. If your exterior is getting too hot, add insulation. If it’s still getting too hot, add more!
As for firing door size, it should be as wide as the widest part of your oven opening, and at least as tall as the opening is high — preferably at least a few inches higher. In effect, you’re making a baffle (to restrict incoming air), which also serves as a short chimney. Distance out from the face of the oven should be 2-3 inches — enough so as not to restrict flow of exiting smoke/gases. Feel free to holler back if this isn’t adequate…
thanks Kiko for your reply. I found an old water heater today. So I’m ready to have the firing door cut out of it!!
If 2-3 inches is okay. would 4 inches be better or worse?
How did you attach the spring coil handle?
THanks again!!
Marty
Hey, Marty, good questions. The short answer is that the amount of standoff is really determined by the curvature of the material you’re using, right? If you’ve got a 12” diameter heater and a 12” wide door, the standoff will be half the diameter, or 6”, right? My oven is bigger, and has a 15” wide door; the firing door came from a bigger cylinder, and stands off about 4”. Obviously, you can bang on the metal to adapt as needed. I’d say try it out and watch how it works. It’s fun, too, to note that the issue opens the door (pun!) to a bunch of interesting stuff. For clean combustion, your firing door should allow roughly the same amount of air to go in as goes out. This, however, is somewhat complicated, as the rate of outgo, or draft, really determines the rate at which the fire draws in air. (This turns out to be useful, because if you shrink your intake port, the fire has to suck air in faster — that high velocity is good, however, because it creates turbulence, turbulence whips up the fire, and — boom! Cleaner burn. Which means cut your inlet holes smaller at first, and watch how the fire burns.) So how do you determine if your firing door allows for the right amount of draft? Based on experience and (untested) observation, I’d say that the draft (or chimney size) for an oven of your size should be about 5-6 inches. That’s about 20-30” of cross sectional area. A 12” wide firing door w/3” of standoff gives you about 25” squared (here’s the calculator). Ha! But don’t worry too much about the numbers. I learned about cross-sectional area later, when I started building rocket stoves and talking to other heater-builders. It’s good to know now, but the knowledge wouldn’t mean much if I hadn’t built the ovens and watched the fires…
I just created this manual on teaching a two days oven course, its a free guide with lots of info. It covers Pedagogy, Technical logistics of the course, building your own tools and how to use an earth oven
You can now download the manual as a PDF here –
https://www.academia.edu/12121029/Facilitating_an_Earth_Oven_Course
as a printable manual (single fold) here –
https://drive.google.com/file/d/0B5t_blchjdPtcXd0VUpjcjFHS3M/view?pli=1
as a free e-book here –
https://play.google.com/books/reader?printsec=frontcover&output=reader&id=BRazCAAAQBAJ&pg=GBS.PT25
A number of years ago I was able to find and use information on the Internet to help me build my wood burning brick pizza oven, and I created my own web site to help others. http://www.ozarkdreams.com contains step by step pictures with comments of my pizza oven which was based on plans from Rado Hand http://www.traditionaloven.com.
Over the years I have added to the site with hints from what I have learned from using our oven and from others who continue to share.
I have been baking sourdough bread for the last three years and pizzas for years before that. As learned more about sourdough baking my interest started to turn to wood fired ovens. After reading both “The Bread Builders” and Kiko’s “Build Your Own Earth Oven”, I decided to build a cob oven to make my entry into wood fired baking.
Having built a steel bbq smoker a few years back, I felt comfortable with the idea of cooking with wood in an offset heat environment.
(smoker build)
https://www.youtube.com/watch?v=YKmIeVGsqNU
Building a cob oven that would use both indirect heat as well as stored heat was new to me, so Kiko’s book was a fantastic source of knowledge.
I started the build this last spring (2013) with the hopes of completing the project before the heat of summer arrived. Unfortunately the heat arrived a month early this year and I was forced to wait until the temps cooled enough to complete the work this fall.
The results were wonderful! The oven is solid and bakes like a dream. Thanks to Kiko’s fire building video and the knowledge in his book as well as The Bread Builders”, my learning curve on using this new oven has been painless!
Here are links to the build video as well as my photos including the first two bread bakes!
The video/slideshow of the build
https://www.youtube.com/watch?v=d98hV_ZvlB4
All the pictures including the first two bread bakes!
http://www.flickr.com/photos/chism/sets/72157636234018985/
Hey, Tom! Thanks for posting this — beautiful oven, and documentation. Richard Miscovich’s new book, From the Wood-Fired Oven (Chelsea Green) has been inspiring us to try new uses/dishes — the current favorite is roasted (whole) onions, done at the top of the heat cycle, in the coals, just before (and maybe a bit after) you clean out the fire. But we’re still working through the book…
Best wishes,
— Kiko
I’m in the middle of reading Richard’s book myself. It’s giving me some ideas!
Beautiful pics of everyone´s projects, and I love Simon´s blogspot photo journal of Breadtopia´s earthen oven. I live in Guatemala and am about to undertake the construction of a wood-burining sauna. I want to make the fire chamber function as an oven as well – or at least be integrated with it. Does anyone have any ideas on this? I´m thinking a large fire chamber in the bottom and above it, half inside the sauna, half outside, where the oven would be. I would so very much appreciate any perspectives!
Laura, for this kind of project you might consider something more along the lines of a rocket stove, which will heat up your sauna a lot faster than an oven is likely to do — tho I do like the idea of using the “waste heat” from the firing of your oven — but what happens if you want to sauna after bake day and the pizza party? Do you have to go back and get the oven hot all over again? If you haven’t already, take a loot at the Rocket Mass Heater book; if you’re already familiar with that, the Rocket Stove bulletin board (http://donkey32.proboards.com/search) is a good place to learn and get advice. In particular, there’s a “batch feed” design that some folks have been building in which the firebox can serve as an oven after the fuel is burnt out. Good luck and let us know how you get on!
— Kiko
This past summer I built a Kiko Denzer style earthen oven in St Marys, Ontario, Canada. The oven is 36″ on the inside diameter with 6″ of thermal mass and insulated with a ceramic fiber blanket around the dome and wine bottles and clay/mulch slip underneath the hearth slab. I have since built a shelter for the oven to protect it from the elements. It wouldn’t have been possible without the generous help of several family members. Thanks also to Kiko himself who provided some very timely advice when I was making some key design decisions.
Building the oven allowed me to expand a home bakery operation whereby I could sell my baked goods at the local farmers market and directly to my customers through a Community Supported Bakery subscription program. I’ve been very pleased with the performance of the oven. I fire it by burning sustainably harvested hardwood for about 8 hrs to achieve full heat saturation. After removing the final coals, the oven rests/soaks for approximately 1-2 hrs. Thereafter I can bake a few loads of pizzas (@650-750F inner dome temp), about five or six loads of bread (15-20 loaves per load @475-575F) and after resting the oven overnight I bake a load of 100% rye bread in tins (@375-425F) and sometimes croissant, danish and cookies. The interior of the oven doesn’t return to the outside ambient air temperature until three days later during which time I often slow roast meat, bake granola, etc.
Construction photos can be found here:
http://breadtopia.blogspot.ca/p/home.html
Feel free to contact me if you have any questions or comments.
beautiful! Impressive collection of photos too — looks like plenty of good help — even one to work the bottom of the ladder! Congratulations. We feed others and so ourselves are fed.
We recently built a Cob Oven at Broadturn Farm in Scarborough Maine. (www.broadturnfarm.com) We run educational programs there through The Long Barn, an independent non-profit organization (www.longbarnmaine.org). We ran an adult workshop with the help of Jesse Stevens. We have been working with the children in our summer camp program cooking in the oven and will be doing a farm to table dinner with them in two weeks. We are fundraising to help cover the cost of materials as well as a timber frame covering structure through http://www.kickstarter.com.
We just finished building our first earth oven at Small Pond Arts in Prince Edward County, Ontario, Canada.
Here’s my blog where you can read all about it!
http://smallpondarts.blogspot.ca/2012/07/outdoor-cob-bake-oven.html
I got Kiko’s “Build Your Own Earth Oven” two years ago and after much thinking and over thinking and building in my mind, I finally got started. You can see my progress at http://backyardpizzaoven.blogspot.com/ I used dry clay I got for $10 for a 55 pound bag at the local ceramic/clay distributor. Pittsburgh is lucky to have a major clay source, Standard Ceramics in Carnegie, Pa. ( 5 miles outside Pittsburgh) When I finally started building the oven with the help of my friends who I call “pizza angels” I just couldn’t stop touching and hugging the dome. I even kissed it! There is something about the earth, truly you have to experience for yourself. If I can build it you can too, I am a 57 year old female.
Thank you Kiko! Your book got me off my rear end and outside actually building something! I had only been dreaming of building natural constructions for the past year and a half until I got your book.
I simply followed your book and I was able to build a beautiful and functional cob oven of my own. I did everything myself. It seemed a little intimidating to do at first, but I just took the plunge and it all turned out great! I feel like I learned a lot of good basics for building with cob. I learned to set a foundation, learned to mix cob and insulation, and I learned how to do a basic lime plastering.
Thanks to your book I now how one successful project under my belt, and I feel very confident moving forward and furthering my practice and education in cob and natural building. I think I’ll build a house next!
Here’s a video I made showing the whole building process for my cob oven.
Im here in Sonoma County active building lots of cob ovens, cob benches, saunas, huts, and even hot tubs. There are photos and videos on my website. Check it out!
Hi
last year we built a clay oven at Fordhall Community Land Initiative, a community owned organic farm in Shropshire, England. A group of volunteers spent the weekend making it in the community growing area so we could grow food, make dough and cook pizza in one area. We had great fun making it and now have fun using it.
best wishes
Bex
Bex wrote to say that there are updates on their news page on the oven build and other neat projects: http://www.fordhallfarm.com/news.php. Looks like they’re doing cool stuff.
With assistance and ideas from Larry Winiarski we built a Rocket Oven that works extremely well using very little wood and making minimal smoke. You can see captioned photos of the process and the final product on a Picasa album. https://picasaweb.google.com/Jonnygms/RocketOven#slideshow/5598633235210438450
Kiko, Thanks for your book and inspiration. We hope you can make it by to see our stove someday.
Jon and Flip Anderson
Follow this link to see my pizza oven chronicle on facebook (you don’t have to be a facebook member.)
hi everyone.
I have been building earth ovens for over ten years, and was fortunate to work with kiko several years ago when we built an oven at an eco event in wales UK. I have since gone on to building ovens from fire cement, mainly for pizza making at festivals in the UK.
I was commissioned to build a very large bread oven on a campsite in sussex UK and i have posted a link to the slide show of the complete process; in addition i ran a week long bread making course, so there are some pictures of some very happy sacred bakers!!
I hope you enjoy them and are suitably inspired, but just to let you know i do not look at emails/computers much so any questions you may have might take a while to be answered.
Michaelthebaker
https://sites.google.com/a/wowo.co.uk/sacredbaking/wowo-oven-build
Hello: So nice to hear from you. Please see our site. We built an oven using Kiko’s book. I also built one with a group once using a willowish basket technique with the Hiram Trust. I have used the one on our website for about 6 years. Children from our programs have made bread every Monday morning during the school year and then our Dragon takes it into his belly and makes the most delicious bread. . . I recently tore it down in hopes of making a new and improved one. If there is any chance any of you would like to come here and do a workshop please let me know you are interested. (Our dragon has been on a journey for about 3 weeks now and I have promised. We are open to slinging mud, working with bees, etc. Thanks for contacting us! (I am not sending this to post these words, just want to contact you. . . don’t see how to post pictures.)
I built an oven following an earlier edition of Kiko’s book and blogged about it under the category Fire, here http://www.nilspeterson.com/category/projects-and-thinking-related-to-sustainability/fire/
I was in a hurry so I built on a wooden deck on saw horses, and as Kiko’s book predicted, it burned thru. Dismantling the oven gave some insights to the failure and to how much firing had ocured in the inner shell, see http://www.nilspeterson.com/2010/11/30/dismantling-my-mud-oven/
I plan to build a new oven on a heavy duty trailer (with concrete blocks above the wooden deck for greater insulation). I’m talking with a local bakery (http://www.panhandlebread.com/PABC/Home.html) about bringing the oven trailer to their booth at the Moscow Farmer’s Market on Saturdays this summer.
Finally, there are two Flickr photo sharing groups that may interest you
http://www.flickr.com/groups/woodfiredbreadovens/pool/with/2098689023/
and
http://www.flickr.com/groups/forno-horno-ovens-woodfired_ovens-kilns-furnaces-heaters/pool/with/2098689023/
David S. Cargo, who assembles info about community ovens for the St. Paul Bread Club sent me a link about Lily Gordon, a remarkable young woman, now 16, who has been helping villagers in Tanzania to build ovens so they can make their own bread (previously, bread had to be transported from so far that it would often be inedible when it arrived).
At the age of 11, Lily Gordon started raising funds for the village of Shirati, Tanzania. For her 11th birthday, instead of gifts, she asked her friends to bring money for the children of Shirati. The party raised $1,300. Behind Lily are many others, particularly a woman named Christine Nyanda Chacha, a Tanzanian woman who decided that lack of parents and money didn’t need to prevent her from going to school, getting a degree, moving to America, and becoming a teacher in Berkeley — where she sought ways to help her students think past the bounds of affluence and entitlement (for more of this story, click here). Lily is just one of many students who have had this experience, thanks to Ms. Nyanda Chacha. Watch the video to hear Lily tell the story:
Here’s a video of an oven I made with my friends in Argentina.
We used homemade adobe bricks and clay mortar.
You can see more of my work at Firespeaking.
I have your book about earth oven and i build a few of those ovens with people in mud building workshops in israel (also giving credit and publication to your book), so i’m eding a few pictures:
1- an earth oven in ein-gedi
2- set of coocking places two of them are rocket stove and one is not
3- a bench made with children and parents in the entrance to a kinder garden.
4-nice detail
and another thing: i’m looking for information about open fire place to make out of mud. i know it’s not as efficient as rocket mass heater, but it has the qualities of having an open fire indoore and it is made only fot occasionaly use (not every day) and in our place it’s not so cold. so if you know where i can get information about it: proportion,shape, how to make it “throwing” as much hit inside, i would like to know..
thank you very much for all the knoledge and inspiration…
riki
p.s. looking at the pictures i thought you might be interested in pictures of a traditional earth oven i once build with old yamanay ladies (mother of a freind of mine and her neighbors) and we baked in it there traditional bread ans cookies so i add a few more
I feel that building an earthen oven is a “gateway” or initiation into natural building. An oven is like a mini building: it has a foundation, walls and should always have a roof to protect it. One learns about how to make “thermal” cob and “insulative” cob, experiments with sculpture… and creates something remarkably functional and beautiful without too much ado.
Here is a picture of the first oven and natural building project that my brother, Alex, and I built upon reading Build Your Own Earthen Oven:
I have gone on to build many ovens since…. here is another one:
You can see other ovens as well as masonry heaters I have built at firespeaking.com.