Moulding (also spelled molding in the United States though usually not within the industry), also known as coving (United Kingdom, Australia), is a strip of material with various profiles used to cover transitions between surfaces or for decoration. It is traditionally made from solid milled wood or plaster, but may be of plastic or reformed wood. In classical architecture and sculpture, the molding is often carved in marble or other stones.
A “plain” molding has right-angled upper and lower edges. A “sprung” molding has upper and lower edges that bevel towards its rear, allowing mounting between two non-parallel planes (such as a wall and a ceiling), with an open space behind. Moldings may be decorated with patterns as long, uninterrupted elements may be boring for eyes.
Decorative moldings have been made of wood, stone and cement. Recently moldings have been made of extruded PVC and Expanded Polystyrene (EPS) as a core with a cement-based protective coating. Synthetic moldings are a cost-effective alternative that rival the aesthetic and function of traditional profiles.
At their simplest, moldings hide and help weather seal natural joints produced in the framing process of building a structure. As decorative elements, they are a means of applying light- and dark-shaded stripes to a structural object without having to change the material or apply pigments. Depending on their function they may be primarily a means of hiding or weather-sealing a joint, purely decorative, or some combination of the three.
As decorative elements the contrast of dark and light areas gives definition to the object. If a vertical wall is lit at an angle of about 45 degrees above the wall (for example, by the sun) then adding a small overhanging horizontal molding, called a fillet molding, will introduce a dark horizontal shadow below it. Adding a vertical fillet to a horizontal surface will create a light vertical shadow.