Combine 1 part fire clay with 1 part silica in a large bowl. Determine the amount of firebricks you need by looking at your kiln blueprint. For example, 1 lb. of silica and 1 lb. of fire clay together will make about eight bricks. If you are making a large quantity of bricks, combine the ingredients in a large tub or mix separate batches.
Mix the fire clay and silica thoroughly using your hands. Use your feet to mix the ingredients for larger batches, if desired.
Shape the clay into bricks using your hands. The most common size is 4 inches by 9 inches by 2 inches. Use a mold, if desired. Measure the bricks to ensure they are the correct size.
Dry the firebricks in a warm place for three days. Flip the bricks over and allow them to dry for another three days.
Place your bricks on kiln shelves so that they are not touching. Put them in a kiln. Bake the bricks for two days at 800 degrees. Ensure all the moisture is removed so that the bricks do not explode during firing or fall apart during removal.
Turn the heat in the kiln up to 2,550 degrees and bake the bricks for another two days.
Turn the kiln off and allow the bricks to cool for at least three days before removing them.