Coping Trim Molding

When installing trim molding 2 methods can be used to join inside corners: mitering and coping. Mitering requires that both pieces of molding be cut at complementary angles. For example, to make a 90° joint each piece of molding must be cut at 45°. Coping a molding joint requires cutting out along the profile of one of the pieces so it butts against the other piece to form a 90° union.

Coping an inside corner is sometimes the best method for joining trim molding because a coped joint will usually not develop a crack along the seam as miter joints can. Gluing a miter joint will greatly diminish the possibility of cracks developing but if you want to be sure you should cope inside molding joints where possible.

Install Piece One

Plan your molding layout and install the first piece so it butts against the wall on both ends. If necessary use two pieces and splice them together with a scarf joint in the middle of the wall.

Cut a Miter on Piece Two

Cut the second piece of molding for the adjacent wall at 45° as if making a mitered joint. Use a compound miter cut if you're coping crown molding. Run a pencil lead along the profile to highlight the edge to be cut.

Cope Piece Two

Use a coping saw to cut along the profile and remove the wood from the back. Hold the blade at an angle sufficient to cut the back off the molding face.

Make multiple cuts from all directions to allow the blade to cut smoothly along each line of the profile. Make as many entry cuts as needed to make cutting easier and chip away at the back of the trim. Turn the molding over and use a sharp drywall knife to shave away excess wood from the back and check the fit. Shave wood from the back until the two molding pieces fit together.

Sand to Finish the Joint

Clean up the face of the cope using a file or sandpaper to leave a sharp line along the molding profile. Work carefully to avoid rounding the point on the front of the molding.

When the two pieces mate smoothly, cut the opposite end of the coped piece to suit the fit the opposite wall corner. If the wall is very long a scarf joint can be used to joint two pieces and finish the wall.