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Plaster and Gypsums

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Plasters and Gypsums

This section contains our plaster and plaster-based products. In its simple form plaster is a mixture of lime or gypsum, sand, and water, sometimes with fiber added, that hardens to a smooth solid. We advise against using traditional Plaster of Paris for art casting as it becomes chalky and flaky over time, does not hold detail well and is hydroscopic, that is when allowed to become damp, can turn irreversibly into a solid form. Instead, the harder the casting plaster the crisper the detail and the more substantial the art piece. CastRite Art Stone is the perfect choice for casting as it sets fairly hard, but yet not hard enough that it can’t be carved or tooled. CastRite is also a great choice for mold making, shell molds and latex slush molds.

When using plasters and gypsum, care must be taken as the chemical reaction that occurs when plaster is mixed with water is exothermic in nature and, in large volumes, can burn the skin. So using plaster against the skin must be avoided.

Plaster Bandages for Shell Molds

Our plaster-based Plaster of Paris bandages have a number of uses. They are all skin safe so that they can be used against the skin with no discomfort or ill effects. Plaster bandages can be used by themselves to make rough body part molds as the capture form, but not detail. The most common use of plaster bandages in mold making and casting is for shell or mother molds. They provide a neat and clean method to add rigidity to the rubber and rubber-like molds such as alginate which once remove from a subject would be formless without hard packing to support it during the casting process.

Using plaster bandages as a mold backing is simple. Prepare the bandage by rolling out about 6-8 inches, roll it back on itself and then roll it back on itself a second time. The result is a collapsed “S” shape. Cut the bandage, stick it and repeat until the roll is finished. You’ll need a bowl of warm water to wet out the bandage. Do not let the water in the bowl become too white with plaster, as the bandage will delaminate later when you don’t want it to. So change the water frequently.

Apply the plaster bandage on top of the mold rubber being sure to smooth it down to prevent mold bubbles. Mold bubbles will create weak spot and dimples in you final casting. Use the flats of your fingers to smooth out the wrinkles. Overlap each triple layer of plaster bandage about one third so that two thirds of each bandage is exposed. The result will provide a very strong shell of 6 layers of plaster bandages when the bandages set.

Plaster Bandages for Masks

Plaster bandages can also be used for mask making. The base mask captures the shape and form of the face of the person on whose face it is constructed. Once the plaster bandages have set they can be carved, built upon, painted and a hook can be added from which to hang.