Zimbabwe' No.1 Food & Recipe Website

How to Build your Own Pizza Oven

Posted On : 3 February 2016 | Category : All Hints & Tips, How To

Building a pizza oven for entertaining family and friends makes for a  satisfying and challenging DIY project. Here we show you how easily it can be done.

MATERIALS
The pizza oven described here is constructed from burnt clay bricks with cement mortared joints.

Bricks
Use well burnt solid clay bricks. Dimensions, especially thickness, should be as uniform as possible. It is not necessary to use face bricks if you are planning to plaster your oven. Cement bricks are not recommended for the dome since they do not withstand heat as well as clay bricks. Always pre-soak burnt clay bricks before building with them.

Mortar
A mortar of fine sand, preferably a building sand and cement is suitable. Use a common cement complying with SANS 50197-1/ SABS ENV 197-1, strength class 32.5 or higher and carrying the SABS mark. It is not necessary to use high-alumina cement, which is expensive and not readily available from retail outlets. The mortar must not be too strong: use 5 buckets of loose, damp sand to 1 bucket of cement and enough water to make a plastic mixture.

Method
THE BASE SLAB
Mark out the required size on the ground. Excavate the area within these markers to a depth of 150-200mm. Use a spirit level to ensure that the surface is level. Compact the area well and wet the ground before placing concrete. Cast the slab in the excavation using medium strength concrete. Your mix proportions should be 1 part cement, 2,5 parts sand and 2 parts stone.

 

 

 

 

Poke the concrete using a broomstick or something similar to ensure there is no voids on the concrete that can lead to weakness and potential sagging. Finish the surface off using a straight edge surface has been levelled, leave the concrete to stand for a while until the surface water evaporates and the concrete stiffens slightly.

The concrete can now be covered with a plastic sheet to prevent moisture loss and ensure effective curing. Keep the slab covered for seven days.

BRICKWORK FOR BASE

Mark out the position and width. Mix a small batch of bedding mortar at a time (1 part cement and 5 parts sand). If too much mortar is mixed it will begin to stiffen before it can be used and will need to be thrown away. Do not add water to mortar that has stiffened to re-temper it as this will weaken it. The base is built up to a convenient working height. We used 12 courses as it is easier to work with the pizzas on a higher level but anything between 9 you build and check heights, remembering to keep in mind that the floor height will be another 185mm higher.

It is very time consuming to lay bricks using a spirit level to line them up. An alternative method is to set up a perpendicular pole/pipe/ broomstick or similar in the centre of the slab and use some form of pointer that rotates around it to indicate the position and height of the bricks.

Unless the base will be plastered, a pointing tool is now used to and make brick laying easier, clay bricks should be pre-soaked. If ‘cement bricks’ are used for the base, they should be laid dry. To allow the mortar to continue to gain strength, it is recommended that the brickwork be kept wet for seven days after completion of the brickwork.

SUSPENDED SLAB
If concrete lintels are used, they need to be carefully chosen. Find a supplier of straight lintels that have been carefully and neatly cast. The lintels will need to be positioned on the base and cut to fit.

OVEN FLOOR
Mark a circle on the concrete slab to indicate the position of the oven base. (A nail and string can be used.) Identify the location of the oven door and build up the brickwork to form the opening. Remember to make the door opening wide and high enough to easily work through and move pizzas in and out (approximately 500mm wide x 310mm high, before paving). The bricks across the top of the door opening require support during construction. The support needs to be left in for approximately a week to allow the mortar to gain strength.

Lay a course of soldier bricks (bricks built up on end) to form the base of the dome. Allow the mortar to set and gain strength for at least 24 hours before any further work is done.

Spread out a 20-25mm layer of 5-7mm stone or river sand over the oven floor to provide some insulation. Carefully level the top surface of this layer to provide a flat surface for laying the clay bricks (face brick). The stone layer is tapered to be thinner near the door to limit restricting the door opening when laying the face bricks. Those in the doorway should be laid in bedding mortar to keep them in position.

Lay the bricks in contact with each other (butt jointed). No grout is required between them. An angle grinder is very useful to cut the bricks around the edges to shape. A hammer and cold chisel can be used to cut these bricks, but it takes a great deal of patience to produce a neat job.

TIPS
• Use soft wood that burns quickly and produces a lot of heat rather than hard, slow-burning wood.
• You know that the oven is hot enough when it is difficult to keep your hand in the entrance.
• If the pizza remains ‘soft’ underneath when the topping is cooked, the floor is not hot enough. (The pizza falls apart into a cheesy mess as you try to turn or remove it, causing subsequent pizzas to stick). Allow the oven to heat properly before cooking, and allow some time between cooking pizzas for the floor to re-heat or alternate pizza cooking positions.

THE DOME
The temporary dome support needs to be constructed with something rigid and strong enough to hold the weight of the dome, but not too strong to be broken out after construction. Materials such as 4mm plywood or masonite are suitable.

Mark two lines on the board perpendicular to each other. The base line length is half the dome floor diameter minus 15mm (dome floor diameter divided by 2 minus 15mm). The dome floor diameter is the diameter of the inside of the soldier course of bricks. The perpendicular line length is equal to the proposed inside height of the dome – approximately 550mm.

Use loose bricks laid on the masonite or plywood to simulate the dome arch shape between two ends of the lines. Remember to allow for the course of soldier bricks already in place. Move the bricks around until a pleasing shape with more or less equal spaces between the bricks is achieved. When an acceptable shape is achieved mark the inside curve onto the board.

Cut out the shape that has been developed with a jigsaw and use it as a template to mark a few more identical shapes. We used these masonite shapes in conjunction with sand – the sand can easily be removed and it makes the mortar joints much better.

Cover the oven floor with a sheet of plastic to protect it from mortar that will drop during the dome construction. Stack the shapes that have been cut for dome support onto the oven floor in the pattern of the spokes in a bicycle wheel. The boards will touch and support each other in the centre of the oven floor. The boards must be evenly spaced around the circumference of the floor.

DOME CONSTRUCTION
It is difficult to construct a nice-looking dome with full length bricks. Begin by cutting approximately 50 bricks into two thirds and one third and approximately 50 into halves. More bricks can be cut into desired sizes as construction of the dome progresses.

Starting with the two thirds-length bricks, begin building the dome. The inside joint widths need to be kept as small as possible. When ‘buttering’ the brick with mortar, taper the mortar to be thin on the inside but thick on the outside. Use enough mortar to allow some to squeeze out when the brick is laid to ensure proper bedding.

Lay the bricks on edge so that they lie as closely as possible to the temporary support. Ensure any adjustments made to brick positioning are made quickly, before the mortar begins to stiffen. If the mortar has already stiffened, it’s better to remove the brick and apply fresh mortar before re-positioning.

Ensure that all the joints are well filled with mortar. Immersing the clay bricks in water just prior to use improves the mortar bond and gives more time to adjust the brick position before the mortar stiffens.

Once the second course of bricks is started, different length bricks are used to ensure that perpendicular joints do not fall directly above each other. The bottom courses are built predominantly with two thirds-sized bricks.

The middle courses are built mainly with half-sized bricks and the top courses with one third-sized bricks. The top few courses will require bricks to be cut into triangular shapes to fit. It may be better to cut these bricks as they are required.

An opening for flue gases must be left in the dome. It’s best to make this opening to one side so that heat does not easily escape out of the top of the oven. An ideal place for this opening is directly behind and above the oven door. An opening approximately 400mm wide and 250mm deep is recommended. The dome construction is quite time consuming. The final oven appearance is directly proportional to the degree of patience and care taken during this stage.

Once the mortar has set, regularly spray the dome to prevent the mortar from drying out too quickly. This will allow it to continue gaining strength. Keep the dome wet for at least a week.

TOOLS
Spade and pick
– Tape measure
– Spirit Level
– Trowel (brick-laying)
– Angle grinder (230mm)
– Masonry cutting disks (5 x 230mm)
– Wheelbarrow
– Jigsaw for cutting board to support the dome
– Marking pen for marking bricks and boards for cutting
– Rubber gloves. Work with mortar is very ‘hands on’ and gloves protect hands from damage
– Pointing tool laying)
– Broomstick, pick handle, 38 x 38mm length of timber or similar to compact concrete etc can be used
– Black plastic sheet for curing

DIMENSIONS
Foundation slab diameter: 2440mm x 1400mm
Suspended slab diameter: 1200mm x 1300mm
Dome inside diameter: 1100mm
Dome outside diameter: 1300mm
Door opening width: 500mm
Door opening height: 350mm

CHIMNEY

Leave the temporary dome support in place during construction of the chimney. The chimney is constructed by building up above the oven door. Two low parallel ‘walls’ form the sides of the chimney. The side walls can extend over the top of the dome if you want it to.

Use a spirit level and tape measure to check levels and dimensions continually in order to produce a good-looking chimney.

FINISHING OFF

Allow at least a week after the dome has been constructed and at least 24 hours after construction of the chimney before breaking out the temporary dome supports. A cold chisel can be used to carefully remove excess mortar that has squeezed out on the inside of the dome. Use a hard bristle brush on loose particles of grit to prevent them from ending up in the mortar to cure and for excess moisture to evaporate before being used.The outside of the oven can be left as it is, tiled, plastered or coated with a fire-proof layer of insulation. It is important to remember that the oven will expand as it heats up and cracks will develop in the dome. These cracks will probably extend into any dome covering and will not affect the efficiency of the oven.

It is important to remember that the heat for cooking does not only come directly form the fire, but also from heat that has been absorbed by the floor an dome of the oven. It is especially important to allow the  oven floor to heat up so that the pizzas are also cooked underneath. For this reason, it is necessary to light the fire several hours before the oven is used.

finished-plastered-oven