The finished earth oven, thanks to a fantastic team of eager participants on a weekend course run by the Loaf Cookery School and led by local artist and earth oven fan Lizzy Bean. It’s been an exhausting weekend, but really great fun and lovely to do it with such a nice bunch of people. Even a torrential thunderstorm on Saturday lunchtime didn’t damped their spirits, although two tubfuls of just mixed cob got filled with about two inches of rain water and had to be redone.
I didn’t get to do much of the actual building myself as I’ve been running up and down the garden delivering regular rounds of tea and cake and preparing lunch for the workers. Mr Greedy Gardener relieved me of kitchen duties on Sunday afternoon and did the washing up while I helped do the final layer, shaped the door and decorated the front with a fossil and some shells.
The process is essentially quite a simple one, using very basic materials and everything was done by hand, or foot in the case of the cob mixing, with no power tools involved. However, the experience of Lizzy and Tom was invaluable with regards to technique, so I’m really glad we didn’t just pitch in blindly ourselves after just reading a book. Getting the right mix of cob for the different layers is important, as is the ratio of the door to the size of oven to ensure optimum heat. The cooking area is about two feet across and the walls are a foot thick.
The costs have been kept minimal by using old tractor tyres for the base, filled with rubble from the allotment, made solid with a weak mix of aggregate and cement. A three inch slab of concrete was laid on the top to insulate the tyres from the heat of the oven. The floor of the oven that the bread etc cooks on is engineering bricks laid on a bed of sharp sand.
The oven walls are made of cob, a traditional building material made by mixing clay and sand, with straw in the outer two layers. The clay was dug up from a friend’s garden and you can incorporate horse hair, cow manure and other materials if you’re so inclined. The first layer of sand and clay was laid over a sand mould which forms the internal oven shape. Then a second layer of a different ratio mix incorporating straw to act as thermal insulation was laid over that. The door was cut and the whole thing finished with a mainly clay layer mixed with chopped straw for strength.
I need to do a bit of tidying up around the edges, not least because my cats have run up the sides of it already and have left claw and paw marks all over it. I also want to do something to cover up the grey concrete slab - the oven itself will dry to a warm brick colour. At the moment, it has a gazebo over it to keep the typically British weather off, but we’ll make a lean to roof over the next few weeks which will also act as an outdoor kitchen. The bricks supporting the door entrance will come out in a few days, then the sand mould scraped out a few days after that. It will need to dry for about a month before cooking can start.
Apparently, earth ovens can last for years and are easy enough to patch up with a bit more cob if they crack. Once they’re up to heat, they cool down slowly so pizza can be followed by bread to be followed by a roast dinner or casserole.
Thanks to everyone who came on the course - it was lovely meeting everybody. We’re planning a reunion when the first firing takes place and a friends of earth ovens group appears to growing where people are offering to help each other out building. The puddling of the clay is a hard slog and best done with willing friends and helpers!
A full photo album of the process is here.