Uses not requiring firing of a finished product include filler for paint and other products and shale and clay used for packing dynamite in blastholes and for plugging oil and gas wells that are no longer in use. Properties Clay and shale are used in so many different structural clay products that they necessarily have a wide range in physical properties. The properties are plasticity, green strength, dry strength, drying and firing shrinkage, vitrification range, and fired color. The properties desired vary with the structural clay product made. For example, a clay used in making conduit tile must be very plastic and have high green and dry strengths and uniform shrinkage, but for drain tile or common brick these properties do not have to be controlled so closely.
Most clays are plastic when naturally wet or mixed with water.
Plasticity can be defined as the property of a material to undergo permanent deformation in any direction without rupture under stress beyond that of elastic yielding. The type of clay mineral, particle size, particle shape, organic matter, soluble salts, adsorbed ions, and the amount and type of nonclay minerals influence the plastic properties of clay. Green strength is the strength of the clay material in the wet or plastic state. Dry strength is the strength of the clay after it is dried. Plasticity and green strength are closely related and are influenced mainly by the same variables.