This is how
a Choose a location and oven size
Choose a location for your cob oven, somewhere you can comfortably hang out with your friends, family, neighbours and everyone who hears about your amazing pizza. Choose a location with good drainage, so the oven isn’t damaged by moisture. It can be situated outside but will require periodic maintenance due to exposure to the sun and rain. If you are constructing it on a verandah or close to a building, it’s probably better to include a chimney, but in an open site, an oven without a chimney is easier to construct.
For an oven that can cook one pizza at a time, the inside oven floor should be at least 750 mm in diameter. A larger oven can be made but will require more wood and time to heat sufficiently. The walls of the oven are about 210 mm thick so enough space is needed for an oven with a full diameter of 1 170 mm.
B Build a solid foundation
One of the mistakes people often make is to build the oven too low. For comfort while cooking, the floor of the oven should ideally be 1 m to 1,1 m from ground level. My base (visible on the main image, previous spread) is made from dry-packed stone but you can also use bricks or stones or wood; just make sure it is strong enough to carry a heavy mud oven. Remember that the height of the base must accommodate a 75 mm layer of sand plus the height of your fire bricks. Note These pictures were taken at a cobbuilding day course, so the demonstration oven was built on the ground and not on a proper foundation.
C Position the fire bricks
Pack a 75 mm layer of well-compacted sand onto the base and embed your fire bricks in it so that you can draw a 750 mm circle (bigger if you want a larger oven) – the bricks only need to cover the inside area of the oven, but must extend out to where the entrance will be. 1
D Create a mould
Using damp sand, make a half sphere as big as the circle on the fire bricks.
The top of the dome must be 375 mm from the bricks (insert a measuring stick and build up to this level). Cover the sand dome with a single layer of paper or plastic (not pictured here; see picture 10 on the opposite page).
Mix the first cob layer (without straw) The next step is to mix the first layer of cob on a tarpaulin. First, mix together clay soil and sand if your soil has too much clay, or add clay if your soil has less than 5% clay. This mixture (which will form the inside walls of the oven) must be smooth and even, with no or very small stones only, so you’ll need to sift it first. 4
E
Now grab a corner of the tarpaulin and pull it to fold it in half. 6 Repeat three to six times with the other ends of the tarpaulin so that you end up with a thick, thoroughly combined, uniform, workable mixture that feels somewhat like gritty clay. 7
Apply the cob
Using your hands, apply the mixture evenly and about 70 mm thick to the sand dome, 9 working from the bottom up (you can use 70 mm long twigs to ensure an even thickness). If the mud starts to slump too much before you have covered the dome, wait an hour for it to dry out a little before continuing.
G Place the door
Position the door against this mud-only layer with the bevelled side and the top facing inwards. Prop it in place with a stone or brick.
Place the chimney pipe (optional) Against the door, build up a pile of bricks to the top of the door and as wide. Place the 110 mm pipe vertically on top of the bricks on the centreline close to the door.
H
I Add straw to the remaining cob
Add a little water to soften the mixture and then slowly add straw and mix it in.