Incorrectly strengthening a shelf can result in bowing or breakage of the shelf. Bowing occurs when you overload a shelf with too much weight or create too long of a shelf that won't support much weight at all. Breakage occurs when the shelf itself breaks or when it pulls away from fixtures at its edge, such as nails, screws or walls. Additionally, you must know how to support a shelf that hangs on a wall as opposed to a shelf inside a big bookshelf. Because such bowing and breakage can prove difficult to fix, prevent it before damage occurs. Once you do, your shelf will remain straight and true.
Position the metal "L" brace beneath the shelf needing support. Metal "L" braces measure 6 to 8 inches in length and can support an entire shelf. Shelves that hang on a wall need middle supports that connect to the centre of the shelf and the wall, so make sure you invert the "L," so that one edge rests upward against a shelf's underside and the other portion of the "L" brace rests flat against the wall.
Screw the upper section of the "L" brace into the centre of the shelf using the wood screws and the screwdriver.
Screw 1/4-inch holes into the drywall using your power drill.
Tap the drywall plug into the hole using the hammer.
Screw the wood screw into the drywall plug using the screwdriver.
Measure the shelf in a bookshelf with the measuring tape. For pre-made bookshelves, you should use a vertical support beam to bolster any shelf longer than 36 inches because lightweight material will cause a long shelf to bow over time.
Cut the 1-inch by 6-inches by 24 inches board to match the distance between the shelf you want to support and the shelf beneath it using the circular saw.
Slide the board beneath and in the centre of the shelf needing support. This board will serve as a vertical support beam between the two shelves.
Screw the L-brackets into place using the wood screws and the screwdriver. Make sure to position them approximately two inches in from the support beams outer edges.
Using a vertical support beam will create two pockets or small shelves in the shelf area beneath the shelf you want to support. For aesthetic purposes, you can cut the width of the vertical support shelf to measure half or three-quarters of the width of the shelf.