The term “clay tape” is an informal label used in crafting for a specific sculpting material. It offers a quicker, cleaner alternative to traditional paper mache. The material is molded and shaped when wet, hardening into a durable, clay-like shell that forms a permanent structure.
Identifying Clay Tape Materials
The product most frequently referred to as “clay tape” is plaster cloth, also widely known as plaster gauze, plaster wrap, or rigid wrap. This material consists of strips of cotton or synthetic gauze fabric that have been coated with a fine powder of plaster of Paris, which is primarily calcium sulfate hemihydrate. The dry, powder-coated strips are inert until they are exposed to water, which initiates a chemical reaction.
When the material is submerged, the water mixes with the calcium sulfate hemihydrate, causing it to rehydrate and crystalize into solid gypsum. This process creates a malleable, wet medium that can be shaped easily over a form or armature. The resulting structure is lightweight yet rigid, making it faster than traditional paper mache, which can take days to dry. Unlike self-hardening clay, this material is structurally supportive immediately upon application over a framework.
Application Techniques
The process of using plaster cloth begins with preparation, which involves cutting the material into manageable strips before activating the plaster. The strips should be sized according to the contours of the project, with smaller pieces used for tight curves and larger strips for broad, flat areas. Before application, the strips are quickly dipped into warm water, ensuring the entire surface is wet but not saturated to the point of dripping, which could wash away too much plaster.
Once saturated, the strips are applied directly to a rigid armature, such as one made of wire, crumpled aluminum foil, or cardboard. It is important to press the material down firmly and smooth it with your fingers as you work, which helps activate the plaster and blend the fibers of the gauze. The strips must be overlapped in multiple directions, typically in two to three layers, to build adequate strength and eliminate weak points in the final sculpture.
For the best results, you should use your fingers or a sculpting tool to work the wet plaster into the weave of the gauze, completely eliminating the texture of the fabric. This smoothing action helps to create a uniform surface that mimics the appearance of hand-sculpted clay. Paying attention to blending the edges of each strip prevents visible seams and creates a cohesive shell around the underlying form.
Curing and Post-Sculpting Treatment
After the final layer of plaster cloth is applied, the chemical reaction continues, and the material begins to cure into a solid state. This process is relatively fast, with the sculpture becoming dry to the touch within an hour, but it requires a full 24 to 48 hours to completely cure and achieve maximum strength. It is important to allow the piece to air dry naturally in a well-ventilated area, avoiding the use of external heat sources, which can cause the material to dry too quickly and potentially crack.
Once the structure is fully hardened, it can be refined using light-grit sandpaper to remove any small imperfections or rough edges. This enhances the smooth, uniform surface. The cured plaster provides an excellent, porous base for finishing, and most acrylic paints and spray paints adhere well to the surface without the need for a primer. Applying a clear sealant or varnish after painting will protect the finished work and prevent the surface from absorbing moisture over time.