You want to build a wood-fired oven with a cement mix that you can mould. You’ve seen instructions on how to build in brick and adobe but you’ve decided against using them because:

1. brick domes are too fiddly and difficult, and
2. adobe (clay and fibre mix) does not last in the weather.

You want to build a free-form oven that will last outside. This website shows you how to build a wood-fired refractory oven and how to make practical tools that allow you to use the oven.

Detailed instructions and photos include: Principles of construction (see below); Planning the design (see below); Materials needed (see below); Where to position the oven in the garden (click here, part 2); Building the base (click here, part 2); Building the oven floor — insulating layer and refractory layer (click here, part 3); Building the dome — refractory layer, insulating layer and chimney (click here, part 4); The plaster or finishing layer and decoration. The door. Curing the oven (click here, part 5); How to make your own wood-fired oven tools (click here, part 6); Lighting and using the oven (click here, part 7).

Principles of construction of a wood-fired oven

1. The inside diameter of your oven will depend on what you want to cook in it. An oven with a diameter of 750 mm will allow you to cook two 20-cm pizzas at a time (2 to 3 minutes each), or two chickens, or two trays of meat and or vegetables. If you wish to make larger pizzas, plan your oven with a wider diameter.
2. Wood-fired ovens are constructed with refractory material on the inner layer that holds the heat generated by the fire. Around this material there is a layer of insulating material that helps hold the heat in. On top of that is a plaster layer that protects the oven from the weather and allows for decoration if desired.
3. The chimney is placed at the front of the oven near the door. This allows for secondary heating of gases and keeps the heat swirling inside the oven before it makes its escape.
4. The height of the door opening should be 60–70% of the inside height of the dome. 5. A door, that closes off the oven opening, allows for roasting or baking.

Planning the oven

The bread oven shown in the photo above has an inside diameter and dome height of 750 mm (29.5 inches). The refractory layer is 100 mm (4 inches) and the insulating layer is 100 mm (4 inches) thick. The interior dome height is 375 mm (half the diameter of the floor) and the dor height and width are 370.5 mm (60 to 70% of dome height). If you wish to build an oven with a 1 metre-wide interior, increase the refractory and insulating layers to 120 mm; the door height to 60% of the interior dome height; and the door width to half the interior dome width. With a 1 m-wide interior, the oven base will have to be at least 1.24 m in diameter.

Preparing the plan

On a large piece of paper draw up the floor plan to true size. To create the circles, take a 1-metre length of string. Make a knot in one end through which to put a drawing pin or nail. Knot a small loop at 350 mm down the string and again at 450 mm and 550 mm. You can then put a felt-tip pen through the loops, hold the drawing pin at the centre of your page and describe the circles with the felt-tip pen. Once you have drawn the circles, draw in the door as shown above. This real-size plan will be very useful when you are deciding where to position the oven, and when you are building it.

Materials needed for a 750 mm-wide oven

120 kg of cement (3 X 40-kg bags)

20 kg bag of fire clay (buy this from potters’ supplies)

0.5 to 0.75 m plasterer’s sand

20 kg bag of hydrated lime

0.1 to 0.2 cubic metres of vermiculite

200 kg medium pumice (no bigger than 7 mm-sized pieces – 10 X 20-kg bags)

Water to mix.

Hints for building an oven with concrete

Always wear rubber gloves when handling concrete. The lime in the mix will burn your skin and dry out your nail cuticles. Mix it  in a wheelbarrow if you do not have a concrete mixer. Put the dry mix in first and blend well with a spade. Add the water (or wet lime mix) gradually to prevent the mix becoming too wet. Read the instructions for each section of the build to see how wet the mix should be.  Concrete takes two weeks to cure fully. You can build one layer on the next after drying over night. If you need to add another layer, leave the base layer rough, to allow for good adhesion. Moisten the drier base layer before adding the next. To begin building your oven, see Where to position your oven and Building the base.