Sketch out the design that you want to create on your terra cotta mural and decide on the dimensions of the mural. It might be easiest to sketch your mural onto a piece of graph paper, so that you can section the mural off into even sections that correspond to the size of clay that your clay roller can accommodate. The clay roller will be used to roll the clay into 1/2 inch thick sections for your mural.
Section off a lump of clay about 1/2 inch thick that is large enough to roll out for a section of your mural. Flatten out the piece of clay using your hands. Pound the clay with your hands until it is flat enough to go through the clay roller.
Set the flattened piece of clay on the canvas and fold the canvas in half so that it covers the top of the clay. Set the clay roller to 1/2-inch thickness, and place the clay inside the canvas in front of the entry to the roller. Crank the clay roller handle until the clay emerges from the other end. Uncover the clay and remove it from the canvas.
Place the cardboard piece that has been cut to the same size as the sections for the mural on top of the rolled piece of clay. Trace around the cardboard template with the clay knife to trim the clay section to be the proper shape and size. Set the scraps aside.
Sculpt the designs that are to go onto the mural section out of more clay. Press and mold the designs onto the cut-out section until they are blended in. If the sculptures are more than 1/2 thick themselves, they must be hollowed out. If any area of the clay is more than 1 inch thick, it may crack during the baking process.
Cut the mural into tiles. The tiles don't have to be perfectly square, but should be approximately the same size. The tiles should be no larger than 6 inches on any one side. If the tiles are larger than 6 inches on a side they may warp or crack in the kiln.
Remove each tile from the work surface by scraping its underside free with the food chopper. Try to keep the tile as flat as possible. Round the corners of each tile using the clay knife, and rake the back of the tile with the clay rake to provide a textured surface to better bond with the wall. Number the back of each tile so that you know where the tile belongs. For instance, if the tile is from the left section of the mural and is the third tile down, the number might be L3. Allow the clay to dry for a few days, at which point it will be ready for firing in the kiln.
Bake the tiles in the kiln until they are fully dried. This will take up to several hours, depending of the size of the tile. If you do not have access to a kiln, you can take the tiles to a do-it-yourself pottery shop where the tiles will be baked for you. Once the tiles have been baked, they can be painted with glaze and then baked again to allow the glaze to react and seal the tile.
Apply the tiles to the wall using grout, and allow to dry for 24 to 48 hours.