In applying any cast, the basic materials are the same: webril or cotton bunting, plaster of Paris, a bucket or basin of tepid water, a water source (tap water), protective linen, gloves, a working surface, a cast saw, and seating surfaces for the patient and the corpsman. Some specific types of casts may require additional material. 

Short-Arm Cast – A short-arm cast extends from the metacarpal-phalangeal joints of the hand to just below the elbow joint. Depending on the location and type of fracture, the physician may order a specific position for the arm to be casted. Generally, the wrist is in a neutral (straight) position with the fingers slightly flexed in the position of function. 

Beginning at the wrist, apply three layers of webril. Then apply webril to the forearm and the hand, making sure that each layer overlaps the other by a third as shown in figure 5-4. Check for lumps or wrinkles and correct any by tearing the webril and smoothing. 

The plaster of Paris is then dipped into the water for approximately 5 seconds. Gently squeeze to remove excess water, but do not wring out. Beginning at the wrist (fig. 5-4C) wrap the plaster in a spiral motion overlapping each layer by one-third to one-half.

Smooth out the layers with a gentle palmar motion. When applying the plaster, make tucks by grasping the excess material and folding it under as if making a pleat. Successive layers cover and smooth over this fold. When the plaster is anchored on the wrist, cover the hand and the palmar surface before continuing up the arm (figs. 5-4D and 5-4E.

Repeat this process until the cast is thick enough to provide adequate support, generally 4 to 5 layers. The final step is to remove any rough edges and smooth the cast surface. The ends of the cast are turned back and covered with the final layer of plaster, and the plaster is set for approximately 15 minutes and then trimmed with a cast saw as needed.

From the Hospital Corpsman HM3 and 2 Manual