How Does Crown Molding Work?
Crown molding is an interior trim that covers the joint between wall and ceiling. It was first used during the Renaissance by Italian designers who developed an interior version of the cornice, or "geison," of the classical Greek architectural order. Along with wood paneling, it was helpful in blocking drafts and cold air in large rooms and soon became popular trim. It reached its elegant limits during the 18th century when four or five pieces piled up along a wall would form crown molding as much as 18 inches high. Today's homes, with shorter ceiling heights and better insulation, use very simple crown molding or none at all. In fact, crown molding practically disappeared from middle class homes during the 1950's during the post-war building boom. It is still very popular with homeowners, however, and the larger or compound type is still used in public buildings and custom-built homes.
Crown molding is trim cut to rise approximately 30 to 45 degrees away from the wall to the ceiling. The shape that is cut into the wood is called the "profile." Crown molding is traditionally made from hardwood using a router or molded plaster. New materials like medium-density fiberboard (MDF), polyurethane and polystyrene provide less expensive alternatives if the trim is to be painted. Polyvinylchloride (PVC) and a rubbery material called Flex are also inexpensive alternatives, but each has specific requirements for paint adhesion. Each material has a place where it works best. PVC and Flex work well in damp areas where wood might rot or plaster degrade. Wood and plaster, however, are more desirable in formal or public areas. Polystyrene is not as sturdy as other materials. Polyurethane cleans up easily. Flex is extremely resilient, but plaster is rather delicate. The type of material you choose should be determined by where it will be used, any special requirements (like curved walls) and how much you have budgeted for trim.
Crown molding is installed like any other wood trim. Since it stands out from the wall, it's secured to the wall at its base. Triangular blocks at the corner sometimes back crown molding, too. Composite crown molding can be designed using a number of different types of trim, securing each layer individually or to a "box" constructed to hold all of the pieces. The biggest challenge with any type of crown molding, though, is fitting the corners properly. This can be done using a compound miter saw, a bench-mounted circular saw that both cuts the 45 degree angle needed for a square corner and scoops out the material behind the surface to allow the ends to fit together properly. An alternative to investing in a compound miter saw is to lay the molding flat, miter the corners and use a coping saw to cut away the material behind the profile. A third way to cut corners is to construct a box inside the miter box to hold the molding at the angle it will sit on the wall.
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