Building a woodfired oven with clay or mud
After having built a oven for myself, i think it's a nice to have piece of work in your backyard.
Be warned, it takes quite some time to build, but also to use it. It's no substitute for your Microwave... it's rather in the slowfood class, even if you can bake a pizza in 2-3 minutes.

## Step 1: What Type and Size Do You Want?

Depending on what you want to bake and the space available, you can adjust the size of your oven. The amount of material needed doesn't scale linear. My oven needed 4 times the material of a small but usable oven.
In numbers that was 600 kg of clay powder, around 950kg of sand.
In my case, the size was selected because my main use of it is to bake bread and i wanted to be able to use the cookie pans from my electric oven. I also selected the thickness of my thermal layer to keep the heat long enough to bake multiple batches of bread, without the need to reheat.
As a general guideline, i wouldn't go smaller than 40cm/16inches inner diameter. Mine has 75cm/30inches. The thickness of the thermal layer should be no less than 15cm/6inches. Mine has 20cm/8inches.
There are certain ratios between inner oven diameter, inner oven height and oven door height you need to have. The most important here, the oven opening height has to be 63% of the inner dome height. This is essential for a clean burning fire. Further, the inner dome height should be 60-75% of the inner dome diameter. With these ratios and measurements, you can determine the actual measurements for your oven. It's best if you look around for firebricks, before you decide on the size of your oven floor. You should sketch your firebrick layout on a large piece of cardboard 1:1. Then draw the inner and outer shape of your oven on it and cut it out. This will help you in the next step, the form and size of your foundation. You should place the opening of your oven away from the main wind direction. Last but not least you have to plan for a roof of some sort. If you plan to bake in bad weather, make it big enough to shelter you as well as the oven. The oven should be able to breathe, so the moisture can get out.

I would like to strongly suggest for everyone to read the book from Kiko Denzer, "Build your own earth oven". It goes much deeper into the details, he built countless different ovens and shares his knowledge. You will see references to his book throughout this instructable. Don't get me wrong here, you can build a oven with this instructable alone, but maybe you'd like to do it a little different. In this book, you will find different techniques, styles and lots of background information.

Pictures of smaller ovens made at a workshop. One with chimney, made in the sand mound method, the other without chimney was made with the inverted basket method.

## Step 2: The Foundation

Since your oven will be pretty heavy, you will need a stable foundation.
In my case, i had a old fireplace that i used as a base for my oven. A friend made a iron reinforced concrete plate for me. It is 130cm/52inches square and 6cm/2.5inches thick weighting around 350kg. This was a heavy lift for 4 persons. I originally wanted it twice as thick and even larger...
If you don't have a fireplace to convert , you need to make your foundation from scratch.
Depending on where you live, you need to make it frost proof. How deep you need to dig for frost proofing, it's best to ask a local builder. I'd dig at least 50cm/20inches in a frost free zone. Then you can build up walls up to the oven floor height. Then fill it up with gravel, and compress it by jumping. Fill the last 10cm/4inches (minimum) with sand. That's where you will put your firebricks as your oven floor.
What bricks you use is up to you. If you have large stones around, use them. Kiko suggests to use "urbanite", that's scrapped concrete you can find at your local dump.

## Step 3: Ovenfloor

In my case, the size of the firebricks and the height of my ovendoor determined the remaining measurements. The size of my firebricks is 25cm/10inches square and 6cm/2.5inches thick. This is a pretty thick brick, in the smaller oven seen in step 1, the bricks were only half the thickness. The thicker the brick, the more heat it stores, but then the sand under the bricks will also store the heat.
I layed out the bricks first to see how they arrange. Since i wanted my firebricks to "float" in the sandbed, i had to cut them to shape. I used a disk grinder to cut them to shape, i ground down around 6 disks. You don't have to do it this way, in the smaller ovens we just built the ovenwalls onto the firebricks.
I sketched the layout on my concrete plate, in order to build up my foundation. If you have another foundation, you don't need to do this step, since you already have your sandbed to lay your firebricks on.
I used Perlite as a first layer under the sandbed. This insulates the concrete plate from the hot sandbed. Otherwise the concrete plate could crack from the heat. If you like to do this, just add it between your gravel and the sandbed.
Be sure to compact your sandbed very well and flatten it nicely. My firebricks weren't of the exact same thickness, so i had to adjust every single one to make sure my oven floor gets flat.

## Step 4: Building the Sand Mound

To define the interior shape of your oven, you have to build a sand mound. To do this, you also have to insert your oven door. The easiest way to make your door, is sawing it out of wood. It's best to use some fire resistant wood like oak. Before you close your oven for baking, you can soak it in water.
For my oven, i had to mount the oven door somehow. I got it from my neighbor, he has a whole lot of them around in different shapes and sizes. He's a retired blacksmith who still has his shop and is still working, but only on jobs he likes. I wanted to mount it decoupled from the hot oven, so i mounted it to the concrete plate. This was made because of the different expansion under heat. As a next step, i added a ring made of cardboard in order to have the inner walls going straight up. This way, it's easier to remove the ash and i have more usable space for baking. We added some more cardboard to stabilize the sand mound around the oven door. It is important to use "sharp" sand, no beach or round sand. It also needs the right moisture content, otherwise your mound will fall apart. As a further effort to stabilize the mound, we used paper with paste or goo on it. (I'm not sure about paste or goo. I mean the stuff you use on wallpaper.)

## Step 5: Building the Oven / Making the Building Material

This is the step, i was most afraid of. Not because how i made it, but because you may want to go on budget and dig your loam out of your backyard. Although this is perfectly possible, it's hard to tell you the right consistency. This is a tactile thing, so it's hard to describe in words.
I used clay powder that i bought in 30kg sacks. With this stuff it's pretty easy. You only have to mix it with the same amount of sand and half the amount of cut straw by volume. Mix it well and add water until the consistency is right. If you add too much water, just add some more clay/sand mix. We used a large tarp to mix and to knead on it. To mix, roll the tarp from one side to the other, so the whole mix will be rolled and well mixed.
Then you need to knead it well. This is very important in order to drive the air out of the mix. It's best to do this by feet, you have much more power in your legs than in your arms. We thought about mechanizing this process. Mixing could be achieved with a concrete mixer, but i don't think it would work for kneading. I think kneading could best be achieved with a bakers kneading machine, but i couldn't get my hands on one up until now.
We then made bricks out of this mixture and used them for building. You should always keep a 90 deg. angle to the sand form. Try to keep the width of the wall constant over the whole oven. The last piece, or the keystone wasn't made as a brick, it was pressed into place.

Now to the diggers among us. I will tell you what Kiko Denzer writes in his book. I can't go that deep into the details as he does. First because of the time i'd need to rephrase it in my own words and second because i don't want any copyright issues coming down on me. Do yourself a favor and get this book, it's worth every buck.
So if you want do dig, you will first have to remove the fertile topsoil which is darker than the subsoil that is rich in clay. You could also inspect construction sites, if you see them digging a cellar or a foundation. You may ask them to dump a truckload at your place, maybe they have some sand around as well.
This subsoil should (mostly does) contain clay, silt sand and small gravel. Your desired building material should contain from 15 to 25% clay. This stuff is hard to dig. It is sticky and heavy around here and it doesn't crumble as a fertile topsoil would. To recognize it, the shovel should leave a shiny cut mark. If you add water, you should be able to roll it into snakes in your hands and bend it with minimal cracking. You should be able to sculpt it. You could do a test by filling a jar half with your soil, the rest with water. Then shake it well, until everything is dissolved. Stand it upright and undisturbed and watch it. In five to ten seconds, sand will settle out. After 30 or so minutes, silt will settle out. Clay takes from days to weeks to settle. So if your mixture clears in a hour or two, you can't use it, because there is no clay.
Now that you don't know the amount of clay in your mixture, you can do a test. Take a handful of your soil, add as much sand as you think is right and work it into a firm ball. This may take some time, since you want it rather dry and compact. Let it fall to the ground from waist height. If it falls apart, you have too much sand. If it goes flat with no cracking, it's too little sand or too much clay. If it almost holds it's shape without or with little cracking, then you've got it. When you make these tests, be sure to take notes on how much sand and soil you used, so you know the mixture for "production scale".
You should make these tests because of this: clay holds water and this water will evaporate. So your building shrinks. To minimize this effect, use as little clay as possible. (15%) The drawback is a reduced "workability". The mixture tends to be crumbly and needs lots of kneading. I used more clay for my mixture, i knew that some cracks will show up anyway, so using a fatter mixture made for easier handling. You have to decide this for yourself.
In the production mixture, you also have to add some straw, cut up to 2.5 to 5cm or 1 to 2 inch pieces. I added half the amount of the sand by volume. (two buckets of sand, one bucket of cut straw) I have to admit, i bought the straw cut up. If you don't want to cut it manually, try a wood chipper.
It will be pretty hard to mix the soil with sand, water and straw. It's best if you invite your buddies over to help you. Your invitation should include some beers and one or two pizza happenings later on. We were only two, my brew-buddy and me. Sometimes it was a bit depressing, when the work didn't seem to have a end. We were asked to help someone build his oven, after he saw mine. He wanted to pay us, but i told him that it's more important to have a couple of helping hands or even better feet.

## Step 6: Removing the Sand

If you are building with a rather dry mixture, you can remove the sand form right after you finished building. But if you're not sure, better give it a week or two for drying depending on weather and climate. Our oven wasn't completely dry as you can see, but it felt hard to touch. So we removed the sand to dry it out from the inside as well. To speed up the process i burned large candles inside my oven. After another week, i started my first fire. Start it small, and do it daily for a week or so. After this, my oven was dry and i tried my first bread. Resist your pyromanic urges to load it with too much fuel, as you can see on the third and fourth picture. If there is more fuel, than the oxygen can burn, it starts to soot badly and burns out the oven door. And that's not where you want the heat.

After baking a couple of batches of bread and pizza, i added a layer of insulation. My oven was almost a 100 deg Celsius 212 deg Fahrenheit on the outside, without insulation.
If you want to do this, think of it from the beginning. That means plan your foundation a little wider. I planned my insulation from the beginning, but i wanted to see how it works without. After applying 8cm/3.5inches of insulation made of Perlite and clay, the outside temperature dropped by half, keeping the heat much longer. You can use different materials for insulation, my choice was a foamed mineral. You could use Vermiculite or pumice, but straw or coarse sawdust from a chainsaw would also work. Maybe you need to make a thicker layer to achieve the same insulating effect. I used a sturdy paint mixer in a electric drill to mix clay, Perlite and water. As you can see, it cracked after drying. We used a silicone cartridge, filled with rather thin clay to fill the cracks. We further made a temporary roof with the tarp we used for mixing and kneading the mud mix. The final roof will be made of fiber concrete(ethernit), but it's up to you what you use. Depending on the distance from your oven opening, it needs to be heat resistant. It worked with the tarp and pine wood without melting or charring, but i will use oak where it gets hot.
We will add a thin layer of clay plaster 1cm/0.5inch when we remove the temporary roof. It's easier to work around the oven without the roof. This is only for the optics and it's not much work.

## Step 8: Using the Oven

Now comes the fun part of having such a oven. Maybe the first time you bake, you have not enough or too much heat. In my case, i heat the oven for 2 hours and then take out the remaining ashes. After another hour of "soaking" it's ready to bake. Soaking means letting the temperature even out in the oven. This timing actually matches my normal dough fermenting pattern.
Here you can see a couple pictures of my baking endeavors.
You can see some of my "devices" that i need to bake as well. To remove the ashes, i use a coco-handbrush mounted on a broomstick. I was lucky to get a wooden bread peel for free and one made of aluminum as a gift. I have a infrared thermometer that goes up to 550 Celsius and 1000 something Fahrenheit. You could throw in some flour and see it turn brown. This should happen in 10 to 20 seconds. Then you have the right temp to bake bread.

Since this is my first instructable, forgive me my wrongdoings. Maybe you see some orthographical or grammatical oddities, that's because English isn't my native language.
I will read your comments and correct any errors and omissions, you make me aware of. If there is enough interest, i could make some baking instructables as well. Having a oven isn't the same as using it.

In the meantime, i made a baking instructable for the Challah-like braid. You can find it here:

By the way, the guy you see on the photos is my brew-buddy Willy, someone had to shoot the pictures and that was me. We have a nice homebrewery together and brew on a (more or less) biweekly basis.

Thomas

## Step 9: Pizza Pizza

Today, we just had a little pizza roundup.
I think it speaks for itself, what such a oven can be good for. It was a very nice gathering. The pizzas came out very well, the flammenkuchen's too. First we looked that everyone had one pizza, so the first hunger was stilled. Well, actually, there was a shrimp cocktail before, some little antipasti and some bread as well. Then i started to do flammenkuchen's and cut them up into small slices, so everyone could take as much as they wanted. Later we had some coffee and cake. Still later, some more flammenkuchen and pizza. As you can see, i had a peppering help from a young fella. At some point, i will learn to shape those pizza's and flammenkuchen's nice and round, but in the meantime they just taste great.
<p>Hi, </p><p>Great Instructable! I am thinking about building a pizza oven of my own and wondered how to keep the oven hot. Do you light the fire then take it out? Do you leave it in there and bake around it?</p>
<p>Hi, </p><p>thanks for you positive comment</p><p>It depends, what i bake. When making pizza, i keep a fire going at the side. I also keep the door open. This way, i can bake pizza for several hours at a more or less constant heat. It needs some experience and a contactless thermometer helps a lot.</p><p>When i bake bread, i take the fire out. Anyway, it's a good idea to bake bread with &quot;falling&quot; heat. (starting high and let it cool down with the door closed)</p>
<p>Nice article mate. I'm creating an series of articles on pizza ovens. Feel free to have a look and perhaps try a slightly different design (eg. Barrel vault or Neapolitan dome) for your next oven. </p><p>http://pinkbird.org/w/How_to_build_a_pizza_oven</p>
<p>Hi Eli</p><p>A lot of text, you wrote... nice!</p><p>Before i built my oven, i also did some research on different designs. I originally built it for baking bread. When i attended a cob building workshop, i asked if i can bring some dough to bake. I fired up a (dry) oven made in a earlier workshop and the bread came out fantastic. Later i found out, that the bread came out so good, because of the prolonged fermentation... and not (only) the oven.</p><p>I don't think, i will build another oven. At least not for me... I'm quite happy with mine. I built one at the workshop, then mine and then one for a friend. I also bought a used professional electric pizza oven two years ago.</p><p>A friend in Germany built a barrel oven with firebricks. He told me about his build, it took him quite some time and stash.</p><p>Now i'm enhancing the doughs and toppings ;-)</p>
Definitely a good plan. I agree once you've got your oven working you must spend time perfecting the actual pizza! :) You never know, you may move in the future and will want to build a new oven at your new place. <br><br>Regards, Eli
<p>&quot;Here pictures of my latest build. Smaller and faster to build. <br>Instructable will follow.&quot;</p><p>Where is the newest instructable? BTW. I am making WFO in a few months and this is the template I will be using. Thank you.</p>
<p>I will see, what i can do...</p><p>Anyway, this will be only a foto report of the build with cross references to this instuctable. I don't find the time to rewrite it completely. (So many projects, so little time ;-)</p>
This is awesome! I just built a pizza oven in my back yard. It's not as easy at it looks, believe me, but well worth the effort! I got my hands on this detailed step by step guide, helped out a lot, check it out <a href="http://www.buildapizzaoven.org" rel="nofollow">www.buildapizzaoven.org</a> <br>
Awesome oven. Thanks for the tips. We made one with clay dug from our lake. It makes tasty pizzas, stuffed mushrooms and bell peppers..and actually it makes everything taste better.
Very nice <br> <br>Here pictures of my latest build. Smaller and faster to build. <br>Instructable will follow. <br>
Nice! that is very sleek and compact. We put a vent at the top of ours, but I'm not sure if that really helps or hurts the design.
If you want a vent, you should place it close to the front. <br>We built one with vent at a workshop. <br>But you loose heat in such small outdoor ovens. <br>I don't care, if it smokes out of the front opening. <br> <br>
cool. nice smoke stack. is that a clay ball at the top?
Exactly, but it didn't tightly fit. So we still lost some heat. <br>When i did that again, i would wait until the smoke stack is somewhat hard. <br>Then place a plastic film on it and press the ball in place, so i get a tight fit. <br> <br>We also had some kindergarten teachers in our group. They wanted this design ;-)
Ah, nice idea.
Hi clay Pizza oven lovers. aside from my blog (http://clayoven.wordpress.com) I have now produced a downloadable eBook containing everything you need to know in order to build your own oven. Have a look and tell me what you think:<br><br>www.clayovenbook.co.uk<br><br>Happy building!<br><br>Simon<br><br>:-)
Hey Simon,<br>does your eBook sell?<br><br>Check out this site, if you haven't already.<br>http://www.varasanos.com/PizzaRecipe.htm<br><br>It's a long read... i PDFed it and put it on my Android phone to read offline.<br>I made a dough for a &quot;Flammkuchen&quot; with his method (hydration and wet kneading) and it's amazing. I made it with yeast only, i'm still waiting for the delivery of my sourdough cultures.<br>I kept it in the fridge for 3 days. <br>I made it in my 300&deg;C electric oven on the pizza stone.<br><br>Try it, you won't regret it.
Wow that guy clearly has a pizza obsession! Amazing.<br><br>S
Yeah, he went all the way.<br><br>The section about different flours and kneading techniques is very enlightening.<br><br>It's the most secret-revealing text, i've ever seen. <br>And best of all, he speaks from his own experience.<br><br><br>By the way, i'm going to build a oven for a friend this spring. It will be a bit smaller and without a door.<br><br>The foundation is already built and my big bakers kneading machine for kneading the building material is already on his property.<br><br>Maybe i take some photos of the building process. My brewing buddy, who helped on my oven will also help. So i guess we can finish it in two days.<br>
I'm VERY intrigued by this &quot; big bakers kneading machine&quot;!<br><br>S
Doesn't seem nice to advertise your book on the back of someone else's intructable.
All of the instructions to build the oven are also still freely available on my blog but I know some people like a good old book. Also, my oven is different to the one featured here. <br><br>Simon
Technically you are right, but it's ok with me. <br>Look at it as further reading.
Too complex. <br><br>Simple brick oven = faster.<br><br>or temporary mud/clay/earthen oven. Just enough for a year or two's worth.
I wouldn't say that.<br><br>I'm enjoying it the fourth year now.<br>As long as the roof stays up, this oven will survive me...
I agree. Mine is almost 4 years old now and although it has had quite a battering (I have neglected it a little to be honest) it still works great. Have a look at my latest post and video showing the winter damage:<br><br>http://clayoven.wordpress.com/2012/03/12/winter-damage-again/<br><br>I fired the oven up immediately afterwards and she worked just like the first day she was built.<br><br>S
Now i need to learn how to make pizza!!!! HAHA
Try this text, it's very long and very thorough.<br><br>http://varasanos.com/PizzaRecipe.htm
hey could i use handmade bricks or ed bricks for this
I don't see, why not. <br>As long, as the ovenfloor is insulated from the foundation, you can take about everything. We used a wooden structure for the temporary ovens in the workshop.
oh okay i just love handmade bricks and was wondering hey have you thought of useing a eltric heater as well as fire for heat
I have thought about electric heating, but to in order to heat up such a monster(in terms of thermal mass), you'd need quite a couple of kilowatts. What your standard wall plug delivers, woult take very long to heat it up.<br>I was also thinking about propane or natural gas heating. Here you can crank out 10+ kW at a reasonable price.<br><br>But then, why do i build a wood fired oven in the first place? Because i love (controlled) open fire.<br>It has a Zen-like quality to fire up the oven, while the dough is rising.<br><br>When it's dark, after making many pizzas in the afternoon, i take a chair, throw some crackling pinewood into the oven and watch the flames.<br>That's better than most TV-programs, especially with a homebrewed beer or a red wine at hand...
yeah i just meant as a added benfit
Thomas, that was a FANTASTIC Instructable! Great job and your English is just fine. Thanks for sharing!
i was wondering what is the color of the clay? because in my country we seem to have high rich clay content in our soil. and also would the oven survive heavy rain because 6 months is of the year is the rainy season and we don't have snow so frost is not a problem. and when i dug in my yard i found a hard dark soil under the gravel
Well, clay comes in different colours. My building clay was brown when wet and beige when dry. <br>For the final touch-up layer, i used a red one.<br>But i have seen from light to dark grey and even blueish clay.<br><br>If you let a ball of your dug dark soil dry, it should get stone hard. It will also be somewhat brittle and have some cracks due to drying shrinkage.<br><br>If you don't want your oven to be gradually washed away, you need to protect it from rain. (A roof also helps to keep the pizzaiolo dry ;-)<br>The clay is not fired on the outside, so it stays water soluble.<br>
thanks ill try that and when i dug in my yard i had to use a pickaxe to get to the dirt because it was so hard that i couldn't use a spade, so maybe its a good sign? and by the way it had rained only a week ago and the dirt is very hard now.
i just made a small ball last night and how its rally hard like a stone and when a dropped it from shoulder height it cracked and broke like a brittle rock and like you said it formed some cracks due to shrinkage. i think that this would be a great material if i let it mix with sand
I have some old concrete 'urbanite' - it has a really high aggregate content - do you think that would work?
I didn't have to do it, so you have to judge for yourself. If you have it around, use it.<br>I would pick up stones from a nearby creek, because i don't have &quot;urbanite&quot; around.
Thanks - I'll give it a shot - great instructable.
hi - I was wondering, the River Cottage Bread book has some instructions on this - and they suggest doing three layers - innner, 'insulating' (with woodchip mixed in the clay' and outer. Any point in doing this?
I don't know this book, but it certainly makes sense. I did it somewhat similar. The inner layer is also called the thermal layer. It's made of clay, sand and shredded straw. The thickness has to be 4-8 inches. This gives the thermal mass of the oven. (mine is close to 8 inches) This means the oven keeps the heat longer, but also needs more time and fuel to heat up.<br>I did some test bakes with only this layer, but i planned a insulating layer from the beginning.(you can see the oven without insulation in step 6 picture 3)<br><br>The oven got quite hot on the outside, so i made a insulation with a perlite clay mix.(perlite is a foamed mineral like pumice)<br>The outside temperature fell by half, keeping the heat even longer.<br>With woodchips, i guess the insulation needs to be a bit thicker than mine.<br><br>The third layer is for protection and good looks only. I did it with a red clay and fine sand.
I myself will be building two of these this summer. After a lot of reading it appears that your door ratio may be a little on the large size which would result in a large heat loss. Would you agree with this?
Hello<br><br>as described in step 1, the calculation only covers the heights of the door and the inner height of the dome. The width of the door can be smaller of course. I just used, what was available at that time. (i wanted a minimal width to use the trays from my electric oven) The opening also doesn't have to be rectangular.(In most ovens i've seen, it isn't.
Hi t.rohner!<br><br>You can also build this oven making a mold with fine and wet sand as you want inside. Cover with clay, as you did. When dry, open the door and take the sand out for next building. You may use soil cement in a ratio of 18:1 with bamboo slivers either to build the oven or to cover it. Ok, it's a little bit more expensive.<br><br>How much water to use with soil cement? Get in hand some clay and squeeze. Falling just a drop of water is perfect. <br><br>To avoid cracks mix sugar with clay. Warning: the mass is slightly softer with sugar. Wait to dry completely and fire strongly. Using cement, don't forget to wet for 3 weeks, to keep cement cold and just use after 30 days. You can use sugar with cement too. Very good! <br><br>Then, good pizzas, good breads and much more!
Dude you AWESOME !!
amazing... thankyou, you've inspired me.... I'm going to start collecting materials and plan for my own oven. Have wanted to make one for about a year but have never been brave enough on my own even with lots of research!! This is a very helpful concise and enjoyable instructable to read...will try to enlist the help of my friends with the promise of pizza and home made champagne!! :-)
Thank you for your nice comment. Some help is definitely desirable. What kind of champagne do you make? I used to make elder flower &quot;champagne&quot; for years. This year i made elder flower sirup. It's very nice in a glass of prosecco or champagne.(even with plain water...)
I'm curious why you didn't use quicklime, the fireproofing and waterproofing ingredient i've read about in cob books. I've made mud bricks in Mississippi climate, they just melt away in the rain, without quicklime added. I submerged a quicklime brick in water for over a year and it remained hard. <br /> I'm guessing the temperature of the oven turns the clay into ceramic? But I wonder if the straw burns without the lime to protect it?