Clear an area for your hearth oven by removing grass and plants. The area should be larger than the circumference of the oven itself. Place the hearth oven away from the house, other structures and trees.
Build the foundation of the oven by placing clay or sand in a circular shape on the cleared dirt patch. Arrange the cinder blocks and firmly compact them into a circular shape on the clay or sand. This creates a fireproof foundation for the hearth oven.
Add another layer of bricks or cinder blocks to insulate the bottom of the oven and raise the hearth off the ground. Approximately 40 inches high is average for an hearth oven.
Build the oven form by placing a dome of compacted sand on top of the hearth, in the size you want the oven. Mix the mortar with water as instructed on the product bag. Place bricks on top of the sand dome in an arch shape. Affix the bricks of the walls and domed roof by applying mortar with a trowel. Make an arched doorway at the front of the oven.
Let the mortar dry completely for several days to firmly set the bricks. When dry, dig out the compacted sand through the arched doorway of the oven. Sweep and wipe away any remaining sand to completely hollow out the oven.
Place a standing grill inside the oven. Use your hearth oven by placing coal or wood beneath the grill and using the top to bake, grill or cook.