How to Install Three-Piece Crown Molding

To mark the miter cuts for outside corners, you'll first mark the ceiling for the upper molding (and the soffit for the lower molding, as shown) to see where the ends of the pieces will land. Position a scrap piece of molding in place so that one end extends beyond the corner. Trace a light pencil line onto the ceiling (or soffit) along the top edge of the molding, extending the line past the corner. Repeat for the other side to create a set of crosshair marks. Position the length of molding to be installed along this line and the fascia (or wall) so that one end extends beyond the corner. On the face of the molding, mark the spots where the top edge meets the crosshair line and the bottom edge meets the corner. Draw a cutline on the face of the molding between these marks. Repeat for the other side.