Even a strong wall shelf will only be able to bear a little weight if it's attached to the wall with the wrong hardware. For a wall shelf to be practical and secure you must use the right hardware for the wall type. Check if your walls are concrete, plaster or wood. There are hardware for all wall types. If you can, try to determine what part of the wall is load-bearing. The most secure place to mount a shelf is on the bearing part of the wall.