Cut the board into usable parts. All boards break differently, so the cut depends on the board. Cut all the jagged edges off, and mark the board with a pencil to create one long, flat side to put against the wall. If you are using a piece of wood, draw a half-surfboard shape with a pencil on the board starting at one of the top corners. The basic shape is pointed at the top and wider at the bottom (see Resources).
Cut along the pencil marks with a saw to make the basic shelf shape. If using the back side of the surfboard, leave the fin attached for added detail. Cut the shape with a jigsaw for the smoothest and straightest cuts. If you do not have access to a jigsaw, score the board with a utility knife and cut the board with a hack saw.
Sand any rough edges on the board to prevent cutting yourself. Sand the whole board if you are cutting from wood.
Apply a primer to the board if you are going to paint it. If you plan to leave it as is, seal the board to protect it from further damage.
Paint the board however you would like. Allow to dry and apply a sealant to protect the paint from chips or damage.
Hang the shelf by attaching brackets to wall studs and placing the shelf on top. Then, screw through the brackets into the shelf.