Thick layers of mortar and insulation are the key to creating an effective wood-fired oven. This traps the heat inside the oven's dome and evenly distributes it onto the pizza. Temperatures inside a well-constructed oven will reach up to 700 degrees F and trap the heat for up to five hours.
Insulate the Oven
Sealing heat inside the dome begins with insulation. Use general house-building mortar to stack the first brick layers. Apply a clay-based refractory mortar when a flat firebrick joint is no longer possible. Add lime to the mortar to slow its drying time. This will give you some extra time to perfectly position the bricks. Lay industrial-strength aluminum foil over the brick surfaces to compensate for contraction and expansion. Follow this with a layer of 10-gauge mesh. Create a plywood form around the oven's dome and leave a gap of about three inches. The thicker the cladding, the less time you have to wait for the oven to heat up. Fill the gap with cement and allow it to dry overnight. Follow the cladding with a layer of refractory insulation to prevent heat from escaping through the top and sides of the oven. This light insulation absorbs heat and keeps unsightly cracks from forming.
Apply two layers of stucco using a serrated trowel to give the exterior a rustic bumpy surface. Build a chimney from red brick during the two days it takes for the oven to dry. Set a spark arrester at the top of the chimney.
Oven Dimensions
Most of a pizza oven dome's height is made up of insulation; the cooking area inside the oven is quite small by comparison. This adds to the goal of retaining 75 percent of the heat and allowing 25 percent to escape through the chimney. A 62 to 64 percent ratio between the oven door's height and the interior ceiling of the dome is equally important. For example, a vault height of 16 inches equals a door 10 inches high. The door's width should not allow heat escape, but don't build it so small that oxygen cannot reach the cooking fire. Mix fire clay and sieved sand in water and spread it on the oven's floor. Set refractory bricks into this mixture; don't join them with mortar. Hammer the bricks into place for an even surface.
Oven Test
Start a cooking fire and give the oven at least an hour to build up heat. Sweep out the embers and ashes when the fire is ready and allow the temperature to cool to about 400 degrees. Slide in your pizza and let it cook.
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