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In the past, architectural mouldings were often made of stone especially granite, marble and lime and also out of wood especially poplar, cherry, pine, and mahogany as these can be carved and reshaped. But today, interior crown mouldings are being made with either Plaster, polystyrene, glassfibre reinforced gypsum (GRG) or wood and exterior cornice mouldings are made of polyurethane, fiberglass or glassfibre reinforced concrete (GFRC).
Plaster moulding: is also referred to as plaster of Paris, may also be used to create complex detailing for use in room interiors. These may be geometric (simulating wood or stone) or naturalistic (simulating leaves, vines, and flowers) These are also often used to simulate wood or stone detailing found in more substantial buildings. Plaster expands while hardening, then contracts slightly just before hardening completely. This makes plaster excellent for use in molds, and it is often used as an artistic material for casting. Plaster is also commonly spread over an armature (form), usually made of wire, mesh or other materials, a process called direct plaster.
Plaster molding can be used in a wide variety of application. Moldings, finials, and other design elements allow designers to incorporate styling from a certain era or stylistic period. Moldings can be practical or decorative, depending on placement, and the molding’s profile can help enhance interior aesthetic. Installing crown molding is an easy and effective way to alter the aesthetic. Though plaster products are inexpensive, plaster products are substantially heavy and will break easily if knocked or dropped. It is also very labour intensive installation process and not waterproof so will damage if any moisture gets to the products.
Polystyrene moulding : is an ideal medium to base the lightweight moulding upon due to the fact that it is a non-biodegradable substance and that it does not absorb moisture Products are exceptionally tough, can be installed with a simple glue application. It is cost effective. Some of the disadvantages of polystyrene are although the products are manufactured from high density styrene, the density is low compared to the urethane products, and hence the product can dent very easily. Only acrylic or water based glues and paints can be used and the products will change colour over time and requires paint. Patterns are not as clear as the polyurethane products.
Polyurethane molding benefits are dramatic. It is also easier to install than wood molding, It is a high density product that will not dent, chip or crack. Paint and glue of any make can be used and paint techniques can be done on the polyurethane products, since the pattern definition is very high. The products are treated and are therefore fire retardant and has insect repellant built in to the products.
Expanded Polystyrene (EPS) is less dense molding with similar attributes to that of polyurethane. Commonly referred to as Faux Stone, EPS trim is best used in applications where the final look of the trim is that of stucco, concrete or a sandstone finish. The ability to fabricate EPS into almost any shape or design make the faux stone material an excellent choice for customizing part without the added costs of carving and tooling.
Commercial grade moldings: Fiberglass and GFRC and aluminum are used for the exterior and GRG is used for the interior. Fiberglass is a lightweight, durable material. It is an excellent product for reducing installation and building costs. Since it is lightweight, fiberglass crown needs less structural support on the building loads. Installation costs are reduced because there is no need to use cranes and booms to lift the material into place and man hours are reduced for the installation. GFRC molding is extremely durable and is the choice of many architects who desire that certain strength to a project. GRG is an interior molding specified for its zero combustibility rating. Many malls, casinos, government buildings, hospitals and other industries use GRG for that purpose.
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