A tandoor clay oven is a traditional East Indian oven that has fired-clay walls, is very well insulated and is heated with charcoal briquettes. You can buy a commercially manufactured oven but it will cost you hundreds or even thousands of pounds depending on the model you choose. Alternatively, you can make your own tandoor oven for very little money. With a little sweat equity you can both build a tandoor oven and be cooking your favourite East Indian dishes in it all in the same day.
Find or buy a metal container wide enough in diameter that a 42.5 cm (17 inch) diameter red clay flower pot can be set rim down inside it. It's all right if the widest outside face of the flower pot makes contact with the inside wall of the metal container. Do not use any container made out of galvanised metal. The oven gets very hot and will burn off the zinc in the galvanised metal creating caustic fumes. Copper or stainless steel make good containers.
Set the clay flower pot rim down on a solid work surface. Put on safety glasses and use an electric angle grinder fitted with a diamond grit wheel to cut the bottom off of the flower pot. Start the cut about 1.8 cm (3/4 inch) above the bottom of the clay pot. Save the cut away clay pot bottom to use as a lid for the oven while heating it up.
Set the bottomless clay pot rim side up on the work surface. Make a mark on the rim and measure off and make a mark 7.5 cm (3 inches) from the first one. Measure down the side of the pot 3 inches below each mark on the rim. Use a ruler to connect the marks to create a 7.5 by 7.5 cm (3 by 3 inch) square.
Drill two holes in the clay pot using a 6 mm (1/4 inch) masonry drill bit. Drill a hole at each of the two inside corners of the square drawn on the side of the pot. Take the angle grinder and cut along each of the three lines drawn on the pot. The drilled holes at the corner will keep the stress off of the clay pot when you make the right-angled cuts.
Shovel sand into the bottom of the metal container, enough so that when it's smoothed and firebrick is set on top of it and the clay pot is set on top of the firebrick, the top, cut edge of the clay pot will be even with the top edge of the metal container.
Fit the firebrick as needed to create the floor of the oven. Use a hammer and chisel to size the firebrick. Sweep dry fire clay into the cracks between the firebrick with a paint brush.
Set the clay pot rim side down on the firebrick. On the outside of the metal container mark the location where the 7.5 cm by 7.5 cm (3 by 3 inch) cutout is on the clay pot. Lift the clay pot back out and drill a 7.5 cm (3 inch) diameter hole through the wall of the metal container.
Set the clay pot rim side down on the firebrick and line up the cutout in the pot with the hole in the metal container. Cut a 7.5 cm (3 inch) diameter steel pipe long enough to run from the inside wall of the clay pot to the outside wall of the metal container. The pipe will act as the air intake bringing oxygen to the briquettes so they will burn.
Mix fire clay and water to make a thick paste and, from the inside of the flower pot, use it to seal the crack between the rim of the clay flower pot and the firebrick floor. Also use the paste to seal any spaces between the steel pipe and the clay pot and the steel pipe and the wall of the metal container.
Fill the space between the outside wall of the clay pot and the inside wall of the metal container with vermiculite. Vermiculite can be bought at garden centres. It's used to mix into potting soil and at one time was used to insulate walls in houses. Bring the vermiculite up to about 2.5 cm (1 inch) below the top edge of the clay pot.
Mix up bricklayer's mortar with water and apply a layer of it on top of the vermiculite. Bring the mortar up to the top edge of the clay pot. After the mortar is in place and smoothed, take a knife and run it all around the inside edge of the metal container. This will create an expansion gap for when the concrete heats up and expands during the firing of the tandoor oven.
The clay liner can also be formed out of raku clay. Either throw a liner on a potter's wheel or hand build one using the coil pot method. The dried raku liner will have to be fired in a kiln before it can be used in building the tandoor oven. A small steel drum works well for the metal container.
An angle grinder is a powerful tool that can hurt you if you don't know how to use it properly. It's not uncommon for the clay liner to crack from the intense heat of the oven. This doesn't mean you can't still keep using your tandoor oven.