workers create walkways, floors, patios, and panels by exposing marble chips and other fine aggregates on the
surface of finished concrete or epoxy-resin. Much of the preliminary work of terrazzo workers is similar to
that of cement masons. Marble-chip, cementitious terrazzo requires three layers
of materials. First, cement masons or terrazzo workers build a solid, level concrete foundation that is 3 to
4 inches deep. After the forms are removed from the foundation, workers add a 1-inch layer of sandy concrete.
Before this layer sets, terrazzo workers partially embed metal divider strips in the concrete wherever there
is to be a joint or change of color in the terrazzo. For the final layer, terrazzo workers blend and place
into each of the panels a fine marble chip mixture that may be color-pigmented. While the mixture is still
wet, workers toss additional marble chips of various colors into each panel and roll a lightweight roller
over the entire surface.
In the 1970s, polymer-based terrazzo was introduced and is
called thin-set terrazzo. Initially polyester and vinyl ester resins were used as the binder resin. Today,
most of the terrazzo installed is epoxy terrazzo. The advantages of this material over cementitious terrazzo
include wider selection of colors, 1/4 inch to 3/8 inch installation thickness, lighter weight, faster
installation, impermeable finish, higher strength, and less susceptibility to cracking. The disadvantage of
epoxy resin based terrazzo is that it can only be used internally not externally. Epoxy based terrazzo will
lose its color and slightly peel when used externally, whereas cement based terrazzo will not. In addition to
marble aggregate blends, other aggregates have been used such as mother of pearl and abalone shell. Recycled
aggregates include: glass, porcelain, concrete and metal. Shapes and medallions can be fabricated on site by
bending divider strips or off site by water-jet cutting.
When the terrazzo is thoroughly dry (or cured in the case
of thin-set terrazzo), helpers grind it with a terrazzo grinder, which is somewhat like a floor polisher,
only much heavier. Slight depressions left by the grinding are filled with a matching grout material and
hand-troweled for a smooth, uniform surface. Terrazzo workers then clean, polish, and seal the dry surface
for a lustrous finish.