A clay oven is a great feature that allows you to bake your own delicious pizzas, breads, cakes, and whatever you can think of. Charlotte and I just built one for the Wangunsari Permaculture Project in Bandung that turned out beautifully – so if you would like to build your own here is how we did it!
- Some gravel (optional)
- Materials for the base (such as large rocks)
- Bricks (you will need roughly 40)
- Straw (wheat straw, rice straw, or whatever you can find)
- A tarp (preferably one you don’t mind getting dirty)
- Some sheets of old newspaper
Step 1 – Designing your oven
Before you can start building you will need to make up your mind about where you will place your oven and how large you want/need it to be. You should make sure to place it in relative location to where you will eat your pizza and/or bake your bread so probably close to your terrace or the kitchen. Evidently the size of your oven will determine how many pizzas or breads you can fit in at once – keep in mind though that a pizza in a properly heated cob oven only takes about 2 minutes until it’s ready! Usually for non-commercial use an inner diameter of roughly 80cm should do the trick. Plan in another 30-40cm to account for the oven walls (15-20cm on each side) and you will know how large your base needs to be.
Step 2 – Building the base
Once you’ve decided on a location and size it’s time to build the base. Dig a roughly 20cm deep hole into the ground that has the shape of your base (so probably round), fill in some gravel (if you have some, if not don’t worry about it) and start piling up your rocks for the base to form a circle. As the outer walls of your base build up you can fill in the middle with spare rocks and gravel. Keep going until your base is stable and roughly hip high (or however high you want your oven to be, just keep in mind that we’ll be adding another 5-10cm of clay and a layer of bricks on top of th base) and more or less even on top.
Step 3 – Testing, mixing, and stomping the clay
Now it is time to get your hands dirty! You will need to mix your clay with sand, straw, and water in order to get the cob mixture that will become your oven. What is the ratio between clay, sand, straw, and water? That depends on the clay content of your clay: if you have a fairly high clay content you will be using roughly 50:50 or 40:60 clay to sand, and if your clay is rather sandy already you will be adding less sand. If you are unsure about the clay content of your clay you can test your clay, but in my experience cob is a fairly forgiving mix to work with and as long as you don’t use pure clay or almost no clay you should be fine! So, put out your tarp and throw a good amount of clay, a good amount of sand, and roughly the same amount (volume, not weight!) of straw on there. Pour a little bit of water on top (not too much at first) and start stomping!
You will be stomping for a while now (Charlotte and I put on some techno music to keep us motivated!), how long exactly depends on the amount you are tackling (doing smaller amounts at a time is a lot easier). Keep adding water if you feel like your mixture is too dry and keep folding the cob like a dough by pulling in one side of the tarp at a time. Your mixture should not be too soggy nor too dry. To test for consistency smash a handful of cob on the ground: if it splatters it is too moist and you will need to add more sand, if it does not flatten from the impact it is too dry. Keep stomping, folding, and adjusting the moisture until you have one solid mass with no pockets of sand and straw left – now your cob is ready!