Clay ovens have been used for thousands of years and are again becoming popular with the renaissance of gourmet pizzas and fine breads. They also can provide exceptional cooking for meats and vegetables. Called tandoors in India, they are also known as earth ovens, pizza ovens and brick ovens. They produce exceptional quality food through the combination of three types of heat: radiant heat from the clay, convection heat from the moving air and steam, and conduction heat from the brick. Almost anyone can build a simple wood-fired oven with little expense and about 12 hours of labour.
Pour a round or square floating foundation pad, 5 to 6 feet in diameter, above ground on a bed of well-draining gravel. This gives you a solid, level building place. Flat rocks or bricks are an option, but concrete is faster, easier and cheaper. The foundation size depends on the oven size; you will build one that is 18 inches deep and 19 inches wide.
Place concrete blocks on the slab to raise the oven level off the ground. Mortar them into place. Raise it higher if you prefer, using more bricks. Use S-type mortar so that it won't crack under the heat of the fire.
Lay and mortar fire bricks on top of the concrete blocks. Lay and mortar square side walls and back along the outside edge. (The front of the oven is open.) The bottom bricks cover the concrete blocks as much as possible. There will be a slight edge of concrete left uncovered. This is insignificant, as later it will be covered with clay or stone and mortar.
Build the walls up to about 18 inches on the outside edges, creating a three-sided box with an open front. Allow the fire brick mortar to dry completely.
Use thin plywood to build an arched form for the roof. Cut the plywood about 6 to 8 inches longer than the oven width, then bend and wedge the edges into the top row of fire bricks. Different plywood types flex differently, so you may have to experiment with length.
Lay and mortar fire bricks over the arch form. Once the mortar has set, remove the plywood by bending it and popping it out. Make sure the mortar has set before removing the form to prevent collapse.
Cover the concrete bricks and fire brick oven with a 4- to 6-inch layer of clay adobe. You can use other materials if clay is not available, like a straw, cob and concrete mortar mix. Field stone can also be mortared around the fire brick. However, clay adobe is the most common, easiest choice. It should be moist and sticky enough to spread easily over the structure, but not so wet that it slides off.
Allow the clay to dry thoroughly, then start a small fire in the oven. Do not build too large of a fire. You need just enough to warm up the bricks and clay, to evaporate any remaining moisture and thoroughly cure all the mortar. Allow to cool.
Build a wooden door for the oven. Cut 2-by-4 or 2-by-6 boards to the width of the front opening. Secure them with two vertical crosspieces. Hold the door in front of the oven and mark the curve of the stove arch. Cut the arch curve with a jigsaw or band saw. Check fit and trim as necessary. This door will not be in place when the fire is burning, but is used to hold heat in the oven during cooking.
This is not a difficult project, but it does require the use of multiple skills and disciplines. It is a great project for the adventurous do-it-yourselfer to learn some new skills.