Rik Midgley - Ceramics - Cob Ovens - NVC - Qigong
The process of making a bread oven is really not so hard and I would encourage anyone interested to give it a go. The chances are that it will work for a reasonable period of time, and the experience of making it will ensure that future ovens are even better. It's life span will depend upon the cob strength, the exposure to the rain, and the stability of the foundations. The secret is to go for it and not to be too afraid of making mistakes. There are two basic designs:
The traditional single chamber bee-hive shaped oven. In these simple ovens, a fire is built inside the oven, and later removed so that the bread is baked from the heat capacity of the oven. (Wait a few moments before putting the bread in or else it will burn). Alternatively they can be very large and the fire can be alight at the same time as baking, which would be handy for pitza making. Either way, the height of the entrance arch must be about two thirds of the internal height of the oven. The oven door may be wooden. If built on foundation stones to keep the damp off, and not allowed to get too rained on, these ovens can last many years.
An oven with an underground fire box. This is the design that we have developed and often build. A fire may burn continually so that the oven can be used for pre longed periods. However with the firebox dug into the ground, dampness and heat stress will result in a collapse of the firebox with pre longed use. This can be overcome be lining the firebox with bricks.
THE BUILDING PROCESS
The first thing to do is to find some clay rich earth. This may be everywhere around, or you may have to go hunting around a river or seashore. A clay soil when wetted, will 'sausage' in the fingers and not crack too much when bent. Collect sufficient quantity of the soil into a container and soak it overnight to soften any lumps. Drain off any excess water.
For the fire box, dig a hole about 20x20x100cm long, depending of course on the number of loaves you wish to bake. For the floor of the bread chamber, a sheet of metal (we use an old run over barrel or the side of an old fridge) is laid over this ditch. At one end there should be a gap of about 10cm to allow heat from the fire box to enter the bread chamber. The gap at the other end should be sufficiently long to enable wood to be fed into the firebox.
Make a former for the cob by pushing hazel rods into the ground in a rib-like structure. Interweave additional rods perpendicularly and also additional pieces for any appendages required, although if this is your first oven, I strongly recommend that you keep things simple.
The cob is made by putting the slacked down mud onto a piece of old tarp and stomping on it to break down it's structure. Dry hay is added, in small amounts to stop knotty lumps forming. This acts as rebars to hold the wet cob together and also helps to dry out the mix. It will burn out during firing leaving insulating holes in the cob. Sand can also be added now if the mud is very rich in clay. This reduces the shrinkage of the cob thus helping it to stop cracking when it dries. When the cob has grown too big for the tarp, simply fold it all into the middle and start again. Repeat this a few times until the cob is lump free and even in constituency.
Place cob onto the metal sheet to protect the bread from burning underneath. This will probably break up a bit anyway, but a higher soil or sand content here will help. Cob can now be built over the entire structure, making sure each piece is well molded in. It should be a minimum of 5cm thick, twice this will add strength and insulation. If you are not making the oven into a silly shape, a flat top, or parallel ridges along the back are useful so that bread can be placed on the oven to rise in the warmth. Also a castellated chimney can be used to support a kettle and so give the warm water required for bread production.
A single chambered oven can be made on a raised platform to prevent rising damp. The surface of this platform may be leveled using bricks and cob so pitza can be cooked without requiring any trays. A former is made from wet sand in a bee-hive shape, with newspaper on top to protect it whilst adding the cob. The cob can be added in two layers, the first being richer in sand to protect it from the heat of the fire, the second richer in hay to add additional insulation. Adding extra cob to the top will increase the period of time the oven may be used without having to reheat.