Make a rectangular wooden mold. Shape it like a shoe box without a top and bottom. As an alternative, a milk or ice cream carton cut so it's about 2 1/2 inches deep makes an excellent mold --- the waxy coating will make it easier to remove from the brick later in the process. You can make your brick whatever size you want, but the size will affect its drying time.
Make a mixture of about 60 percent soil and 40 percent sand. Add chopped straw and water until the mixture is the consistency of stiff, moist dough.
Place your mold on a baking sheet and pour the mud mixture into it. Pack the mixture down to get rid of any bubbles.
Put your brick in the sun to dry until it is leather-hard (stiff and hard enough to be handled without losing its shape). Carefully remove the mold.
Leave the brick in the sun to dry completely. If you were making your brick in the Mesopotamian desert, it would take about two or three days to dry. You should leave your brick at least two or three weeks in the sun to dry.
Make a more durable brick by drying it in an oven. The ancient Mesopotamians are credited with the invention of drying clay in an oven, or kiln. Let your brick sun dry until it is leather-hard; then remove the mold and bake the brick in an oven set to 300 F for about four hours. The actual drying time depends on the size of your brick.