How Casts Are Applied

Many different sizes and shapes of casts are available depending on what body part needs to be protected. A doctor decides which type and shape is best for each person.

Cast application

Before casting material is applied (plaster or fiberglass), a "stockinette" is usually placed on the skin where the cast begins and ends (at the hand and near the elbow for a wrist cast). This stockinette protects the skin from the casting material.

After the stockinette is placed, soft cotton batting material (also called cast padding or Webril) is rolled on. This cotton batting layer provides both additional padding to protect the skin and elastic pressure to the fracture to aid in healing.

Next, the plaster or fiberglass cast material is rolled on while it is still wet.

The cast will usually begin to feel hard about 10-15 minutes after it is put on, but it takes much longer to be fully dry and hard.

Be especially careful with the cast for the first 1-2 days because it can easily crack or break while it is drying and hardening. It can take up to 24-48 hours for the cast to completely harden.

Plaster casts

A plaster cast is made from rolls or pieces of dry muslin that have starch or dextrose and calcium sulfate added.

When the plaster gets wet, a chemical reaction happens (between the water and the calcium sulfate) that produces heat and eventually causes the plaster to set, or get hard, when it dries.

A person can usually feel the cast getting warm on the skin from this chemical reaction as it sets.

The temperature of the water used to wet the plaster affects the rate at which the cast sets. When colder water is used, it takes longer for the plaster to set, and a smaller amount of heat is produced from the chemical reaction.

Plaster casts are usually smooth and white.

Fiberglass casts

Fiberglass casts are also applied starting from a roll that gets wet.

After the roll gets wet, it is rolled on to form the cast. Fiberglass casts also get warm and harden as they dry.

Fiberglass casts are rough on the outside and look like a weave when they dry. Some fiberglass casts may even be colored.

Source: http://www.emedicinehealth.com/cast_care/page3_em.htm