How to Attach Crown Molding to a Premade Bookcase

Measure the width of the bookcase along the top of the front with a tape measure. This is the length you will need for the front molding. Measure the depth of the bookcase along the top of one side. This is the length required for the side molding pieces.

Adjust the miter saw to make a 45-degree angle cut. Measure and mark the measurement required for the front molding piece on the back side of the molding stock.

Place the crown molding on the miter saw with the front side facing up. The top edge should rest against the fence and the bottom edge should rest against the table of the saw. Cut a 45-degree angle on each end. The front will be the long side with the angles shortening into the back edge. The measurement from the back side will be the measurement required for the front molding piece.

Measure and mark the length required for the two side molding pieces onto the back side of the molding stock. Cut one 45 degree angle on each end of the side molding pieces using a miter saw so that they fit with the front molding piece to form a three-sided rectangle. The measurement from the back side will be the measurement for the side molding pieces.

Fit the side and front pieces together under the top lip of the bookcase top.

Hammer finish nails through the molding every 3 inches into the book case to fasten it together.

Center the nail set onto the head of each nail and strike the top of it with a hammer to set the nails 1/16 inch deep into the surface of the wood.

Fill the nail holes with a putty knife using wood putty. Allow the putty to dry for 24 hours.

Sand the putty with fine-grit sandpaper in the direction of the wood grain.

Apply a matching wood finish to the molding with a paintbrush. Allow the finish to dry 24 hours before using the bookcase.