How to build a wood-fired pizza/bread oven using local natural materialsIf you are looking for a small project to get your hands (and feet!) dirty testing out some natural building skills, then building a wood-fired oven is a great place to start. If you have a little help, it takes just a couple days to build, then a few weeks to let it dry out (during which time, you can sculpt your oven to any shape), and then you're ready for a pizza party!!
What is a cob wood-fired pizza oven?? Well...it's a baking oven that is heated by lighting a fire inside, the fire warms up a thick clay oven wall, and the clay wall remains warm for hours after the fire is pulled out. So you build the fire in the same oven area that becomes your baking space. The beauty of this type of oven is a) the oven is simple to build using local, natural materials and b) the oven temperature remains very even throughout, with no hot or cold spots. Plus, it's a fun project to do with a bunch of people and you can celebrate your accomplishment with a pizza party!
So, what do you need to know to ensure that your oven project is successful?
FIRST, get this book:
|this book contains all of the information you|
need to successfully build a cob oven. Really!
SECOND, decide what size oven you want to build.The appropriate size for you will depend on how you intend to use your oven. Here are the variables effected by size:
- The larger the oven, the more materials you need to build it. For example, an oven that is 36" wide inside takes about twice as much clay, sand, & straw as an oven that is 24" wide inside. And more materials translates to more building time as well.
- The larger the oven, the longer it takes to heat up. For example, a 24" wide oven takes about 2 hours of fire to heat up, whereas a 36" oven takes about 3 hours.
- The larger the oven, the more mass, soooooo, the longer the oven stays warm. This means you can cook in it longer each time you fire it up. Especially if you a good insulation layer on your oven.
- And obviously, the larger your oven, the more pizzas you can bake at once! (Or whatever you are cooking...)
Typical sizes are 22-1/2", 27", or 36" (these sizes work out well with the size of standard fire brick). Of course, there are mini ovens as well as massive ovens, but those are mostly for special use applications.
THIRD, decide if you will build a roof over your oven.
A roof will help protect your oven from the elements, and allows you to bake even when the weather is sucky. Rain, especially, will erode a clay oven over time. You can either allow that, replaster your oven every year, put a tarp over your oven when it's not in use, or....build a roof to protect it. If you decide to build a roof, those materials will be in addition to those listed below. Build your roof so you have plenty of room to stand underneath, and to clear any smoke out. I recommend at least 7 feet of clearance under the roof.
FOURTH, gather your materials.
You will need the following materials to build your oven:
- Clay: Clay is your essential ingredient, because it is the binder that holds all the materials together. When wet, clay is sticky. When it dries, it is strong & hard. You can use clay-soil OR you can purchase dry, bagged, pottery clay. (see video below on how to test your soil for clay content.) If you are using clay soil, you will need to determine the proportion of clay in your soil (it may feel like it's 100% clay, but it rarely actually is...usually there is sand in there as well).
HOW MUCH? The amount of clay needed depends on the size oven you are building. Here I am talking about total clay, so if you are using soil with clay in it, you will calculate the amount of clay based on the percentage of clay in the soil (So, if your soil is 50% clay & 50% sand, then every bucket of soil = 1/2 bucket of clay & 1/2 bucket of sand.) So total clay needed is about 25 gallons for a 22-1/2" oven, about 35 gallons for a 27" oven, and about 50 gallons for a 36" oven.
- Sand: Sand is your aggregate. It reduces shrinkage of the clay as it dries and it adds total strength to your oven walls. You need to use angular sand, not smooth sand or silt. Concrete sand is pretty cheap & works great. I also use sand to build the form for the oven (this sand is taken out at the end and can be used to make plaster if you finish your oven that way).
HOW MUCH? Plan on about 300 to 500 lbs of sand if you are using clay soil with at least 50% sand content; if you are using bagged pottery clay, double the sand.
- Straw: Straw is used to create an insulating layer for your oven. It is also helpful to stand on the bales as your oven gets tall. Make sure your straw is clean, dry, and mold-free.
HOW MUCH? You need about 2 to 3 strawbales for a small oven and 3 to 4 strawbales for a larger oven. If you plan to sculpt your oven into a fun shape, make sure you have ample straw.
- Firebrick: This is what I like to use for the floor of the oven, because they don't split in the heat of the fire and they have extremely squared edges, so they make a really smooth floor. Typical firebrick are 4-1/2" x 9" x 1-1/2". You can lay out the bricks for your desired oven size to see exactly how many you need, but below is what I use as a reference.
HOW MUCH? I use 15 firebrick for a 22-1/2" oven (12 for the floor + 3 for the door opening), 22 firebrick for a 27" oven (18 for the floor + 4 for the door opening), and 37 firebrick for a 36" oven (32 for the floor + 5 for the door opening).
- Water: you will need a running water source to wet the clay binder. (and is helpful for clean-up)
- Newspaper (optional): I use this as a layer between my sand form & the first layer of clay...it lets you know when to stop digging out your sand so you don't accidentally gouge your oven wall.
- Stones or brick or urbanite (optional): I recommend building your oven up on a base so you don't have to kneel on the ground to tend your fire & bake. A comfortable height is typically 24" to 36" off the ground, but choose whatever height is comfortable to you. You can use any kind of masonry material that is available to you, and you can make cob (clay, sand, and straw) to make a strong mortar. Just make sure that your oven base is very stable. Once the base is built & dry, don't forget to fill in the center (with something sturdy & non-compressible), so you have something solid to build your oven floor on.
How to test your soil to see if it has clay in it:
And this is my tools list when doing an oven workshop:
- buckets - I like to have ample 5-gallon buckets; you these to transport and measure your materials; to me, 5 buckets is a minimum, but if you are working alone, one bucket will work
- tarps - I like to have 2 tarps, but one works; 10' x 10' seems to be a manageable size
- shovels - if you are working alone, one shovel is fine; if you are going to have a bunch of people, have at least one shovel for sand & one for clay (more if you will have lots of helpers)
- sifter - if you are using clay soil dug out of the ground, I find it easiest to sift it roughly through a 1/2" screen to remove any rocks & to break up the clay and make it easier to mix; I like a table screen that fits over a wheelbarrow
- a wheelbarrow is useful to transport material, but is not essential
FINALLY, build your oven!
STEP ONE: Build your base
|I like to make a shallow foundation filled with gravel to help keep the oven from moving with freeze-thaw cycles in the ground.|
|You can build your base with any masonry material - this example uses old cobblestones from the streets of Philadelphia, built with a cob (clay, sand & straw) mortar mixture.|
STEP TWO: Fill in your base & build the oven floor
|Fill in the base of the oven with a non-compressible material, like tamped gravel. Then add a 4" or so layer of sand that extend just above the sides of your base. Tamp and level that sand.|
STEP THREE: Build the form for your oven cavity
|Basically, you are building the most boring sand castle ever: a nice dome. The dome width is the diameter of baking space you want. The height of the dome will be 75% of whatever your width is.|
|Add a layer of newspaper over your sand so that when you dig out the sand at the end, you know when to stop digging (before gauging your clay layer).|
STEP FOUR: Build the clay mass layer of your oven
STEP FIVE: Add the insulation layer
STEP SIX: Cut the door
STEP SEVEN: Let the oven dry for a few days, then pull out the sand
STEP EIGHT: Sculpt your oven as desired
STEP NINE: Let your oven dry out completely & then have a pizza party!
Still not clear? Watch these videos that show you the step-by-step process for building a cob oven.Building the floor of the oven & the sand mold for the oven cavity
Building the thermal mass layer (that will heat up when you build your fire) & the insulating layer that keeps the oven hot longer.
Digging out the sand form & baking your first pizza.