How to Frame Built-in Bookcases

Determine the length of the top and sides of the bookcases with a measuring tape.

Pick a type of crown molding. Measure the width of the crown molding, and double the dimension. Add the total dimension to the measurement of the top of the bookcase. For example, if the molding is 4 inches wide and the top of the bookcase is 24 inches, you'll have a total dimension of 32 inches for the top of the bookcase.

Cut a piece of crown molding that is equal to the measurement of each of the sides of the bookcases. Cut a piece of crown molding that is equal to the dimension determined in step 2; this piece of molding will be used for the top of the bookcase. Use either a reciprocating saw or a circular saw to make the cuts.

Center the piece of crown molding cut for the top of the bookcase over the top edge of the bookcase. Secure the molding in place by hammering standard wood nails into each of the ends of the molding. Hammer finishing nails every 6 to 8 inches along the molding.

Place the remaining pieces of molding along the sides of the bookcase. Butt the ends of the molding up against the overhanging edges of the molding on top of the bookcase. Secure the molding on the sides of the bookcase in place by hammering standard wood nails into each of the ends of the molding. Hammer finishing nails every 8 to 10 inches along the molding.

Countersink the nails in the molding. Place a nail set over each of the nails and hammer the end of the instrument against the nails, driving the heads into the molding.

Fill the holes over the countersunk nails with wood putty that matches the color of the molding. Allow the wood putty to dry, and then sand the surface with fine-grit sandpaper to create a seamless look.