Crowns Take the correct measurements. Always install the crown with the bump or convex part on top and the concave part on the bottom. Be sure the crown fits snugly into the corner and against both ceiling and wall. Nail in place. Use a nail set to finish driving the nails. Apply wood filler in the nail holes. Apply caulking between the moulding and the ceiling and the moulding and the wall for better results. Retouch the paint on the nail holes.