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
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