Build the Foundation

• 1). Measure out a 4-foot by 4-foot square on a solid surface. Hard-packed dirt or concrete patio is best.
  
  
• 2). Set 10 concrete cinder blocks around the 4-foot square, with the solid sides facing up. Top these with Liquid Nails or mortar, and build up a second layer of cinder blocks. Be sure to place the second layer of cinder blocks so that they are directly on top of the seams of the first layer. Build a third layer of cinder blocks the same way, and allow the entire foundation structure to set overnight.
  
  
• 3). When the mortar or Liquid Nails adhesive has fully dried, fill the structure with 2 feet of rubble. Top this with a layer of gravel coming to within 8 inches of the top of the foundation structure. Add a 5-inch layer of vermiculite or perlite for insulation, then fill the structure with sand. Use a scrap of lumber or an extra cinder block to tamp the sand down until it is even with the top of the structure.
  
  
• 4). Arrange the firebricks on the top of the structure. Fit them tightly together so there are no gaps.
  
  

Build the Oven Form

• 1). Use the string and pencil to draw a circle on the top of the foundation structure. The circumference should be as wide as the structure. Draw a second circle 7 inches inside the first.
  
  
• 2). Lay out the tarp and dump a load of sand in the center. Wet the sand thoroughly. Use the wet sand to create a dome inside the inner circle on the foundation structure. Mold the wet sand into the exact height and shape you want for the inside of the oven.
  
  
• 3). Measure the sand dome and make a note of the measurement. You will need it later to make the door for your oven. Remove any leftover sand from the tarp.
  
  

Build the Oven

• 1). Mix your adobe. Place 3 parts sand and 1 part clay on the tarp. Mix the sand and clay thoroughly by treading it with bare feet. Use the tarp to fold the pile over on itself occasionally, then stomp or tread it again until it is well mixed. Check the moisture level of the adobe. Pack a 3-inch ball of adobe and drop it onto a hard surface. If it breaks apart or cracks, add more water. If it flattens, add more clay and sand to the mixture.
  
  
• 2). Form rough adobe bricks about 3 inches thick. Use these bricks to build up the first layer of the oven around the sand dome. When the dome is completely covered with adobe, use the 2x4 scrap lumber to smooth out the bricks. Let this dry overnight.
  
  
• 3). Mix another batch of adobe, this time adding in some of the chopped straw. Form 3-inch bricks and build up a second layer of adobe. Let this dry overnight.
  
  
• 4). Locate the measurement you took of the height of the sand dome. Multiply this number by 0.63 to find the height of the door. Use the kitchen knife to cut a door hole in the adobe that is the correct height. The hole should be wide enough to accommodate whatever you plan to bake in the oven. Scoop out the sand through to door hole. Use a small brush or broom to get the last grains of sand off the floor of the oven.
  
  
• 5). Mix a third batch of adobe. This time the mixture should be quite thin, with more clay than sand. Mix in very finely chopped straw. Spread a 1-inch layer of this adobe plaster over the first two layers, leaving the door hole open. Let this layer dry overnight.
  
  

Finish the Oven

• 1). Use tracing paper and a pencil to trace the door hole. Cut out the shape and use this as a pattern to cut the 2-inch lumber into a door. Cut the door slightly larger than the pattern so it fits snugly in the door hole. Use nails to attach the handle to the door.
  
  
• 2). Fire the oven. Use the firewood to build a small fire inside the oven. Let this burn continuously for several hours. Watch for cracks to develop in the adobe. Small cracks are acceptable, but if large ones begin to appear, fill them with wet clay.
  
  
• 3). Repeat the firing process several times a week for two weeks. At this point your oven should be completely dry and ready for baking.