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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.
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.
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Signing UpStep 1What 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.
At some point you need to decide whether you want a chimney or not. I had the chance to use a oven with a chimney, but decided against it for my oven. The main advantage of a chimney is to take the smoke out of your face. The main disadvantage in a simple design, lots of heat will go out the chimney instead of heating up your oven. It also adds complexity to your design. If you need to add a chimney, because your fire doesn't burn cleanly, you can do it even after finishing your oven.
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.
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.
At some point you need to decide whether you want a chimney or not. I had the chance to use a oven with a chimney, but decided against it for my oven. The main advantage of a chimney is to take the smoke out of your face. The main disadvantage in a simple design, lots of heat will go out the chimney instead of heating up your oven. It also adds complexity to your design. If you need to add a chimney, because your fire doesn't burn cleanly, you can do it even after finishing your oven.
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.
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http://varasanos.com/PizzaRecipe.htm
Simple brick oven = faster.
or temporary mud/clay/earthen oven. Just enough for a year or two's worth.
I'm enjoying it the fourth year now.
As long as the roof stays up, this oven will survive me...
www.clayovenbook.co.uk
Happy building!
Simon
:-)
does your eBook sell?
Check out this site, if you haven't already.
http://www.varasanos.com/PizzaRecipe.htm
It's a long read... i PDFed it and put it on my Android phone to read offline.
I made a dough for a "Flammkuchen" 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.
I kept it in the fridge for 3 days.
I made it in my 300°C electric oven on the pizza stone.
Try it, you won't regret it.
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.
I was also thinking about propane or natural gas heating. Here you can crank out 10+ kW at a reasonable price.
But then, why do i build a wood fired oven in the first place? Because i love (controlled) open fire.
It has a Zen-like quality to fire up the oven, while the dough is rising.
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.
That's better than most TV-programs, especially with a homebrewed beer or a red wine at hand...
For the final touch-up layer, i used a red one.
But i have seen from light to dark grey and even blueish clay.
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.
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 ;-)
The clay is not fired on the outside, so it stays water soluble.
I would pick up stones from a nearby creek, because i don't have "urbanite" around.
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)
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)
The outside temperature fell by half, keeping the heat even longer.
With woodchips, i guess the insulation needs to be a bit thicker than mine.
The third layer is for protection and good looks only. I did it with a red clay and fine sand.
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.
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.
How much water to use with soil cement? Get in hand some clay and squeeze. Falling just a drop of water is perfect.
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!
Then, good pizzas, good breads and much more!
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?
The clay in the cob is only fired in a small layer on the inside, if at all. This fired portion will be waterproof, but that's not much help on the inside.
The straw will burn in this layer, leaving holes in the cob as added insulation. Since it's not that much straw in the mix, it's of no concern.
I have to admit, i can't remember having read about quicklime in cob. But a roof also helps to keep me dry, if it starts to rain... and it's easy to build.
Doesn't quicklime reduce the moisture permeability of the cob? This could be a problem with trapped moisture in the thermal layer. The expanding vapor could crack the thermal layer if this happens.
But it could well be, that by the fire in the oven, the slaked lime would be fired back to quicklime and get hygroscopic again.
For general building, it makes a lot of sense of course.
By the way, if you read books, buy the one from Peter Reinhart "AmericanPie" It's all about pizza. I wanted to do a professional 3 week training as a pizzaiolo. But after reading this book, I don't think i would learn much more. Especially since i don't have the intention to do it for a living...
I would like to do it for some time, but my actual job in the tech section is much better paid...
Since most things are less expensive in the US, you should get away under 1000$.
The biggest chunk in my case was the clay / loampowder, then the firebricks and the sand.
If you dig your own mud / loam, you should get away even under 500$.