Chapter 7 Plastering, Stuccoing, and Ceramic Tile

CHAPTER 7 PLASTERING, STUCCOING, AND CERAMIC TILE Plaster and stucco are like concrete in that they are construction materials applied in a plastic condition that harden in place. They are also basically the same material. The fundamental difference between the two is location. If used internally, the material is called plaster; if used externally, it is called stucco. Ceramic tile is generally used to partially or entirely cover interior walls, such as those in bathrooms, showers, galleys, and corridors. The tile is made of clay, pressed into shape, and baked in an oven. This chapter provides information on the procedures, methods, and techniques used in plastering, stuccoing, and tile setting. Also described are various tools, equipment, and materials the Builder uses when working with these materials. PLASTER LEARNING OBJECTIVE: Upon completing this section, you should be able to identify plaster ingredients, state the principles of mix design, and describe common types and uses of gypsum plaster. A plaster mix, like a concrete mix, is made plastic by the addition of water to dry ingredients (binders and aggregates). Also, like concrete, a chemical reaction of the binder and the water, called hydration, causes the mix to harden. The binders most commonly used in plaster are gypsum, lime, and portland cement. Because gypsum plaster should not be exposed to water or severe moisture conditions, it is usually restricted to interior use. Lime and portland cement plaster maybe used both internally and externally. The most commonly used aggregates are sand, vermiculite, and perlite. GYPSUM PLASTER Gypsum is a naturally occurring sedimentary gray, white, or pink rock. The natural rock is crushed, then heated to a high temperature. This process (known as calcining) drives off about three-quarters of the water of crystallization, which forms about 20 percent of the weight of the rock in its natural state. The calcined material is then ground to a fine powder. Additives are used to control set, stabilization, and other physical or chemical characteristics. For a type of gypsum plaster called Keene’s cement, the crushed gypsum rock is heated until nearly all the crystallization water is removed. The resulting material, called Keene’s cement, produces a very hard, fine-textured finish coat. The removal of crystallization water from natural gypsum is a dehydration process. In the course of setting, mixing water (water of hydration) added to the mix dehydrates with the gypsum, causing recrystallization. Recrystallization results in hardening of the plaster. Base Coats There are four common types of gypsum base coat plasters. Gypsum neat plaster is gypsum plaster without aggregate, intended for mixing with aggregate and water on the job. Gypsum ready-mixed plaster consists of gypsum and ordinary mineral aggregate. On the job, you just add water. Gypsum wood-fibered plaster consists of calcined gypsum combined with at least 0.75 percent by weight of nonstaining wood fibers. It maybe used as is or mixed with one part sand to produce base coats of superior strength and hardness. Gypsum bond plaster is designed to bond to properly prepared monolithic concrete. This type of plaster is basically calcined gypsum mixed with from 2-to 5-percent lime by weight. Finish Coats There are five common types of gypsum-finish coat plasters. Ready-mix gypsum-finish plasters are designed for use over gypsum-plaster base coats. They consist of finely ground calcined gypsum, some with aggregate and others without. On the job, just add water. Gypsum acoustical plasters are designed to reduce sound reverberation. Gypsum gauging plasters contain lime putty. The putty provides desirable setting properties, increases dimensional stability drying, and provides initial surface hardness. during 7-1