Having a wood-fired concrete oven at home will allow you to cook more food and cut down on your electricity costs. It’s an easy project to build and it can be used to bake bread, cook meat and a range of other delicious meals.
The oven is made from burnt clay bricks with cement mortar as these materials are able to withstand the intense heat of the fire. The cement required should be strength class 32,5 or higher. It is not necessary to use fire bricks as they are expensive.
Materials needed to make concrete oven
Besides the burnt clay bricks and cement, you will need fine sand for the mortar. Use one part cement to six parts sand and enough water to make a pliable mortar for the brick joints. You’ll need about four or five bags of cement for this project and half a cubic metre of sand.
You will also need some crushed stones for the concrete foundation slab – half a cubic metre should be enough. Order 350 bricks to start and about 60 clay paving bricks for the floor of the oven.
You’ll need some plywood strips to create a support for the dome of the oven. Make sure that you have a shovel, tape measure, trowel, spirit level, angle grinder, wheelbarrow, wooden float, saw, large bucket, black plastic sheet, steel rebar, ratchet strap and a straight-edged plank or piece of metal.
Building the foundation of the oven
Start by marking out a 1.8m diameter circle on the ground. This can be done by tying a string to a peg in the ground and then tying a nail at 90cm along the string. Pull the string and score the ground with the nail while rotating around the peg. Excavate the area inside the circle to a depth of 7.5cm.
Next, compact the floor of the circular hole and wet the soil slightly. Using one bag of cement, two wheelbarrows of sand and two wheelbarrows of crushed stone, mix a batch of concrete with enough water to form a pliable mix.
Fill the circular pit with the concrete and ensure the surface is level by using the straight edge and a spirit level. Leave the concrete to set underneath a plastic sheet for seven days. Keep the concrete moist by spraying a bit of water on it every day.
Building the brick base of the oven
For the brick base, you will need 150 clay bricks, 10 litres of cement (about one-third of a bag) and a wheelbarrow of fine sand. Mix ingredients with water to form a sticky, moldable mortar.
Begin by marking the centre of the concrete foundation with a nail. Tie a string to this nail and tie another nail at 80cm along the string. Score the concrete with the outer nail, giving you a circle of 1.6m in diameter. This will be the guideline for the outside diameter of the brick base.
Start laying the bricks on the concrete foundation, following the circular scoreline. Place a layer of mortar first, then a layer of bricks. Build the base up to a convenient height – about nine layers of bricks should be perfect.
Ensure that each layer of brick is level with the ground and perfectly upright. The diameter of the circular base should remain constant at all levels of the brick base. Once the bricks are laid, leave the base to set for another seven days. Keep it damp by spraying with water twice a day until the mortar has reached a good strength.
Building the suspended concrete slab
The floor of the oven will sit on a suspended concrete slab laid on top of the brick base. This concrete slab will need to be reinforced with six lengths of steel rebar as there will be a hollow space underneath it. You will need some strong wood (19mm shutter board) to create a form that can support the weight of the wet concrete.
You will need two bags of cement, one wheelbarrow of sand and two wheelbarrows of crushed stone. Mix the dry ingredients with water to form a concrete mix – this batch will have more stones than the batch for the concrete foundation.
To create the wooden form, place 19mm shutter board or strong wood on top of the brick base. Cut the wood into a circle that matches the diameter of the brick base, and then cut the wooden circle in half to make it easier to remove once the concrete has hardened. Make sure the wooden board is well supported underneath with brick pillars or wooden poles.
To create the sides of the form, tie a ratchet strap around the top of the brick base. Use the shutter board offcuts to create vertical battens that will be held in place by the strap. Tuck the battens between the strap and the brick base – you’ll need about 15 battens.
Next, cut 75mm wide strips of plywood – make them as long as possible. These plywood strips will be used to create the side of the formwork. Fasten the plywood strips to the inside of the vertical battens using screws or nails. Make sure the gaps between the wooden base and the sides are sealed, as well as the two halves of the wooden base as you don’t want your concrete to leak through the gaps.
Apply a thin layer of grease or cooking oil to the wooden form surfaces – this will help to release the form from the hardened concrete later. Cut strips of steel rebar to match the varying lengths of the circular base and keep them aside. They will be laid in two stages with the wet concrete mixture.
Pour the first layer of freshly-mixed concrete into the wooden form; about 25mm thick once compacted. Lay the lengths of steel rebar on the surface of the concrete in two layers, 90 degrees to one another. Pour the rest of the concrete over the rebar and fill up the wooden form. Compact the concrete again and level the surface with a straight edge and spirit level.
Cover the concrete with a plastic sheet and keep it damp while it cures for seven days. Then, remove the wooden forms and set the concrete slab on top of the brick base.
Building the concrete oven floor
The floor of the concrete oven is made from clay paving bricks. To begin, mark out a 1.4m diameter circle on the top of the suspended concrete slab using string and two nails (70cm apart). Mark the spot where the opening of the oven will go and don’t lay any bricks in that section.
Mix 10 litres of cement with a wheelbarrow of fine sand to create the brick mortar. For the first layer of bricks, lay them vertically around the perimeter of the scored circle on the suspended slab. Leave a gap (about two-brick lengths wide and 30cm high) where the oven opening will be. Build a square archway for the oven door and support the bricks across the top of the door with some wood. The supports can be removed once the mortar has cured for 24 hours.
Now that your door has been created and the first layer of upright bricks is laid, pour in a 2cm layer of crushed stone or gravel onto the concrete base. This will provide insulation for the suspended concrete slab from the oven floor. Compact the stones and level the surface. Lay clay paving bricks over the stones and pack tightly.
No mortar or grout is needed if the bricks are cut to shape and packed neatly inside the circular oven. The layer of stone and paving bricks underneath the oven door can be set in a small layer of mortar to stop everything from spilling out of the oven.
Building the brick dome and chimney
The brick dome will need to be supported by plywood while the mortar sets. This wood is strong enough to support the weight of the dome but can also be easily broken down and removed once the dome is complete.
To make the dome supports, start by marking out the shape of the dome on a piece of plywood. Measure the length of the inner diameter of the oven and draw a line of the same length on the plywood. Draw a perpendicular line upwards from the middle of the baseline, about 55cm long. This will mark the top of the dome.
Use loose bricks laid on top of the plywood to simulate the dome arch. Remember to allow for the layer of vertical bricks already in place around the perimeter of the oven floor. Move the bricks around until a pleasing dome shape with approximately equal spaces between the bricks is achieved.
Once you have your desired dome shape, mark the inside curve on the plywood with a pen. Cut out the shape using a saw and use it as a template to create 12 other dome-shaped supports. Cut each support in half, giving you 24 quarter-circles than can be arranged inside the oven.
Place a plastic sheet on the floor of the oven to protect it from dripping mortar. Arrange the dome supports in a circle inside the oven, like the spokes of a bicycle wheel. The supports should all touch in the centre of the oven floor and should be evenly spaced from one another. Now you can start laying the bricks for the dome.
If you like, you can cut 50 bricks into half and another fifty into one-third and two-third pieces. This will make it easier to construct a nice, rounded dome. Full-length bricks can be used but the dome will be a bit rough and jagged. Mix a batch of mortar (10 litres of cement, one wheelbarrow of sand and enough water) and start with the two-thirds bricks. Lay them on top of the vertical bricks already forming the perimeter of the oven floor.
The bricks should be laid flush with the wooden dome supports. The first two layers of bricks should be made from the two-thirds pieces of brick. Then start using half bricks for the next couple of layers, ensuring that the mortar joints don’t line up with the layers below. The top few layers will be built from the one-third pieces of brick, again, ensuring that the mortar joints don’t line up with the layers below.
You will need to cut a few bricks into triangular shapes to complete the top of the dome. Cut these bricks to shape as they are required. Before laying the bricks for the dome, make sure to leave a gap for the chimney.
The best place for the chimney is directly behind the oven door archway, not in the centre of the dome as this would allow all the heat to escape. Leave an opening of about 40cm by 25cm wide behind the archway and build a brick chimney around this opening on top of the oven door. Two sides of the chimney should also extend up the side of the dome towards the centre.
Take your time with the dome and the chimney, don’t rush it. Once they have been built, keep them moist and allow them to set for at least seven days. Break out the wooden dome supports and remove the plastic lining. Use a hard-bristle brush or a small chisel to remove any bits of hard mortar that have squeezed out during construction.
Before using the oven, leave it to cure and dry for a further two weeks. To use the oven, light a fire on one side of the dome several hours before cooking anything. This allows the whole floor of the oven to heat up, as well as the inside of the oven. Wood or charcoal can be used for the fire.
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