With its lightweight and simple, straightforward design, the Billy bookcase is one of Ikea's signature pieces -- but it isn't invincible. The thin cardboard backing of the Billy bookcase can rip or be punctured, leaving eyesores behind. If that happens, don't go running off to the Ikea store for a replacement just yet. You can replace the back of the bookcase, saving you a trip and the trouble of assembling another piece of furniture.
Remove the bookcase's removable shelves and set them aside. Lower the bookcase onto its face so that the back is facing up.
Pull out the 18 nails holding the back in place with a claw hammer. If they are too far in to grab with just the hammer, use needle-nose pliers to grab and yank them out.
Slide the back of the bookcase out of its grooves. Set it down on another piece of thin cardboard -- it is crucial that they are of the same thickness, to ensure that the back will fit into the grooves carved in the bookcase.
Trace an outline of the backing onto the new piece of cardboard. Cut it out with a pair of strong scissors or a box cutter.
Slide the new backing into place, fitting it in the grooves on the left and right sides of the bookcase and sliding it all the way until it fits into the top groove.
Mark a line on the cardboard backing to show where the middle shelf falls, so that you have a reference with you nail the backing in place.
Hammer the 18 nails back in place along the top, bottom and middle shelves. Avoid using the same holes, if possible. You may opt instead to use a staple gun to staple the backing in place. Lift your bookcase back onto its feet and replace the shelves.