Building a clay oven in your backyard may seem like a daunting process. But after we built ours, I can really say it wasn’t that bad! Now that we have had Big Bill for over 2 years, I’m really glad Native Kiwi insisted we built one rather than my lazy idea of having a backyard swing seat in the same spot.
First of all, you’ll need to plan:
- The size of your oven – this depends on what you want to do with it. (Mine has a floor diameter of 27 inches or 68 cm. If you just want to have the occasional pizza party without much baking, go for 2/3 of this.)
- Where you are going to have your oven.
- Your access to fire wood. (Mine typically takes 1/2 wheelbarrow load of wood in one firing. Smaller oven will take less wood.)
- Where you are going to find a trailer load of clay. (Not pottery grade! We dug ours from a building site on a cliff. You only want 15-25% of actual clay, else it will shrink too much and crack. If you happen to find good quality clay, you’ll need to add sand or dirt to the mix. You can find out how to test your clay in this book.)
- How you want to support the oven (a base). (Concrete is really not the best choice!)
- How to built your oven doorway (brick or just clay etc.).
- If you are going to have a chimney and how you will shut the chimney off (important to be able to shut it off!).
- How you will shelter the oven from the elements (else the clay will melt away in the rain! And don’t even think about putting a waterproof finishing layer on the oven! It will “suffocate” the oven and eventually, moisture will build up from the inside and the oven will collapse!)
- Find materials for the oven:
- firebricks for your oven floor (hearth) (normal red bricks will do too but will crack sooner)
- 1-2 wheelbarrows of sand (from a river or beach)
- a trailer of clay (give or take)
- 1-2 sack of pumice/perlite/vermiculite or just straw
- another 1-2 sacks of straw
I was given the book “Build Your Own Earth Oven” and I really recommend you getting hold of a copy if you are serious about building one of your own.
Planning and finding materials took a long time for us. But once these are settled, the actual building only took around one weekend. (Click here to see how we built Big Bill.) The condensed steps are:
- Build a base for your oven with good insulation. (Concrete is a poor insulator! If we were to build another, I’d go for a solid based filled with landfill and soil.)
- Put a layer of sand on the base and level it.
- Lay the fire bricks for oven floor on the sand.
- Built a doorway for your oven. If you are building a chimney (I really recommend this), leave a hole for the chimney in your doorway.
- Block the doorway and make a sand “igloo” that’s the shape of your oven cavity. (The “golden ratio” of oven floor diameter:oven height:door height is 4:3:2.)
- Cover the sand igloo with damp newspapers.
- Mix up clay to a stiff but very smooth dough*.
- Build the first layer of your oven wall (3 inches thick) by layering tennis balls of your clay dough like brick work. Use “tangential” force (don’t push into the sand) to really compact and stick the clay balls together.
- If you want your oven to be able to hold heat for more than 3-4 hours of cooking at once (like mine), do the following, otherwise go to next step. Mix up more clay “dough”, this time with a softness of your ear lobe (which is softer than 1st layer). Then mix in equal amount of insulation material (pumice/perlite/vermiculite or straw).
- Using the same brick work principal, built a second 3” layer.
- Mix up some clay “batter” to the consistency of a pancake batter. Then mix in 3-4 times the amount of straw so the straws just bond together by the batter.
- Spread this mixture over the oven to a thickness of 3”.
- Finally mix up some clay to peanut butter consistency and add equal amount of straw. Spread over the oven to a thickness of 1” as the finish layer. Fix your chimney on using this “dough” if you are building a chimney.
- Smooth the finish layer all over
- Make a door for the oven (I think using the dough from the finish layer is the easiest option) and give yourself a pat on the shoulder!
- Wait for a day and empty the sand through the oven door.
- Wait for at least a week to let the clay dry. Two weeks to be on the safe side. Make up more clay dough to patch up cracks when they appear.
- When you start your first fire in the oven, build it up slowly over 2 hours, then fire it up for another hour for your first pizza party!
*note: I really recommend getting hold of a electric paint mixer or something of the sort for mixing your clay! Saved sooooo much time for us! Use the mixer to mixed up some “mud slush” then knead in more clay by “dancing” in the mud. Finally, shape and compact a tennis ball size then let it drop at elbow height. The ball should more or less hold its shape. If it crumbles, add more water. If it flattens, add more clay.