Although most people who sport an arm cast are probably in the process of healing a broken bone, anyone in the know can easily make an arm cast to wear for fun or as a prop. An arm cast can be made from a wide variety of materials--including fibreglass, latex, modelling clay or papier mache. The most common and readily available would be a traditional plaster cast made with plaster mix and strips of fabric. With a little patience and skill, anyone can make an arm cast right at home.
Apply a cast stocking to the arm and smooth out any wrinkles or bubbles. This keeps the plaster from adhering to the skin and arm hairs. If a traditional cast stocking is not available, cover the arm in gauze, cling film, a wet sheet, a thin cotton sock or a nylon stocking with the toe end cut off. For a plaster cast that is going to be removed promptly after drying, the arm may also be coated in a layer of petroleum jelly to facilitate easier removal of the plaster.
Wrap the arm in a single layer of cast padding, if the goal is to create the look of an authentic plaster cast. Begin at the wrist and loop the strip around the thumb before continuing down the length of the arm. Be sure to overlap each layer slightly and create a snug fit that will not bunch or cut off circulation.
Prepare plaster. Follow the directions on the plaster container for preparation if using traditional plaster. The plaster can be applied directly, or it may be used to soak bandages or strips of gauze, which will then be applied to the arm in the same overlapping pattern as the cast padding. If using plaster cast bandages, soak them in water for several minutes prior to application. Be sure to work quickly before the plaster hardens. Smooth out any air bubbles and make sure the cast creates a snug fit on the arm.
Allow the cast to harden and dry. Depending on the thickness, this may take several hours. Using a heat lamp or hair dryer on a low setting can help speed up the drying process. The exterior will be dry first, and the interior will dry out last. Be sure to take this into account before attempting removal.
To remove the cast, make a small cut and gently crack it open to preserve the shape as much as possible. Following removal, it can be reattached to the arm as a false cast.
Allow plenty of time for this project, as the cast takes quite a while to dry.