Cob ovens

Space Brazier

Examples of Cob ovens

Cob or unfired clay ovens are the most primitive ovens that one can make and as such are relatively inexpensive and fun to build. Cob as a building material in the UK is mostly found in Devon and Cornwall although there are examples from Cumbria in the north, the East Midlands, Norfolk and Suffolk and down to Hampshire. The integrity of the structure relies on clay as a binder for the aggregate and straw as a strengthener to stop cracking in high shrinkage clays. It is found throughout Europe in vernacular buildings normally protected by a lime render or wash and more widely in arid countries where it is normally called Adobe.

The clays should be tested if dug on site to establish their clay/aggregate proportion but clays can also be bought in powdered form or from brickworks bagged up. For cob ovens, the aggregate should be basically a coarse sharp sand (not rounded beach sand) with angular stones up to 30mm to create an angular ballast a bit like old Hoggin which used to used for paths and road surfaces before Tarmac was invented. The Cob should be mixed in a proportion of 20% clay to 80% aggregate and puddled together by adding water carefully, trampling the material together to unify it. This mix is used for the refractory inner lining of the oven roughly 75-80 mm thick. The outer layers added after this layer contain chopped straw which should also be puddled together until the mix won't take any more straw. This outer coat can be anything up to 150 mm thick and provides some insulation to prevent too much heat escaping the structure. The Hearth is normally firebrick bedded on either fireclay or sand and laid over a 150-300mm layer of insulation in the form of sand, lime/sand/straw, lime/hemp shiv, empty bottles or any other granular insulation material which will achieve a firm base.

In the slideshow below is an example of a build at the Rare Species Conservation Centre, Sandwich Kent and uses a couple of old concrete soakaway rings as a base ( to speed up installation) and a hydraulic lime/sand/straw mix for the insulated base.

Notice also the log store cut out underneath and the soakaway holes providing the ventilation to keep the logs dry!

Another recent cob oven build in Lynsted, Kent.

We are available for commissions to an agreed design and all ovens can be infinitely customisable because of the flexible nature of clay. We have some bagged clay available locally but stock is very variable. Chopped dust-free straw is available at competitive rates should you need some for your own project.

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