4. Hold the molding up on the wall so that one side touches the wall and the other touches the ceiling. The wall edge of the mitered end should touch the side of the corner; the ceiling side will protrude slightly past the corner.Nail it in place with 4d finishing nails in the wall and ceiling edge.. Hold the molding up on the wall so that one side touches the wall and the other touches the ceiling. The wall edge of the mitered end should touch the side of the corner; the ceiling side will protrude slightly past the corner.