Terrazzo

Terrazzo is a building material that has the cross-section of polished rock chips decorating its appearance.
It is a composite material made up of chips surrounded by a binder.  It is poured in place or precast. It is used for floors or walls. It consists of marble, quartz, granite, glass or other suitable chips, sprinkled or unsprinkled, and poured with a binder that is cement-like, chemical or a combination of both. Terrazzo is cured, ground and polished to a smooth surface. Sometimes, it is finished to produce a uniformly textured surface that is not flat.

Production 

Terrazzo artisans 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 (7.6 cm to 10 cm) deep. After the forms are removed from the foundation, workers add a 1-inch (2.54 cm) 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 cement-based terrazzo include: a wider selection of colors, 1/4 inch to 3/8 inch (.63 cm to .95 cm) installation thickness, lighter weight, faster installation, impermeable finish, higher strength, and cracking less. The disadvantage of epoxy resin based terrazzo is that it can only be used inside, not outside buildings. Epoxy-based terrazzo will lose its color and slightly peel when used outdoors. 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 contractors then clean, polish, and seal the dry surface for a finish that shines.

Historical
Venetian construction workers invented terrazzo for use as a low cost flooring material using leftover marble chips from upscale jobs. The workers would usually set them in clay to surface the patios around their living quarters. Consisting originally of marble chips, clay, and goat milk (as the sealer), production of terrazzo became much easier after the 1920s and the introduction of electric industrial grinders and other power equipment.

Newly-set terrazzo will not look like marble unless it is wet. So, they used the goat's milk to act as a sealer and preserving the wet and marble-like look.

Archaeological

Archaeologists use the word terrazzo to describe the floors of early neolithic buildings (PPN A and B, ca. 9,000–8,000 BC) in Western Asia, that are constructed of burnt lime and clay, colored red with ochre and polished. The embedded crushed limestone gives it a slightly mottled appearance.
The use of fire to produce burnt lime, which was also used for the hafting of implements, predates the use of pottery by almost a thousand years.
In the early Neolithic settlement  of Cayönü in eastern Turkey ca. 90 m² of terrazzo floors have been uncovered. The floors of the PPN B settlement of Nevali Cori  measure about 80 m². They are 15 cm thick, and contain  about 10-15 % lime.

Other sites with terrazzo floors include Nevali Cori, Göbekli Tepe, Jericho, and Kastros (Cyprus).

Terrazzo and sustainability

Terrazzo flooring is an original recycled product, created centuries ago by Venetian workers using the waste chips from slab marble processing. Today Terrazzo continues to provide environmentally friendly durability and low maintenance, typically lasting the life of the building. With no volatile organic compounds (VOC), it earns further point on indoor air quality ratings. Recycled content is still a standard feature of modern terrazzo. 

Terrazzo aggregates, binders and finished flooring systems can contribute to U.S. Green Building Council (USGBC) credits, under the LEED-NC rating system, version 2.2.  

The evaluation of a construction product for its environmental impact considers the longevity of the material, the composition, recycled materials, maintenance requirements, embodied energy, and lifetime environmental impact. 

Durability is at the core of green construction. Terrazzo flooring can be refinished repeatedly, reusing instead of replacing materials. It can be restored to its original luster at a fraction of the cost of replacement. Even century-old floors have generally proven need little more than minor repairs and refinishing to return them to their original beauty.

Terrazzo flooring (both cement and thin-set epoxy) also requires only minimal, low-cost maintenance. Routine maintenance should be no more than dry and damp mopping, with an occasional spray buffing. Waxing or chemical cleaners only serve to cloud or damage the finish. Annual stripping and resealing can be done with water-based products. 

Terrazzo is composed of naturally occurring aggregates, recycled glass or plastic and processed cement or epoxy binders. The binders constitute 25-30 percent of the volume of a floor; the remainder is composed of aggregates, pigments and fillers. 

Post-consumer recycled glass or post-industrial stone from slab granite and marble processing increase the amount of recycled content in Terrazzo, along with recycled aluminum divider strips.

Both cement-based and thin-set epoxy Terrazzo systems are made of zero VOC materials.  Terrazzo produces little or no off-gassing over the life of a cured floor. The non-porous Terrazzo finish resists microbial growth and moisture. 

The potential for local sourcing is another environmental strength of Terrazzo. Manufactured on site, Terrazzo installations generally produce minimal post-commercial waste and save on transportation costs. 

On typical projects, Terrazzo can realistically contribute to five LEED credits: MRcr4 (2), MRcr5 (2) EQcr4 (1). Terrazzo may also potentially contribute to MRcr1 (1), and in extreme cases, ldcr1 (1), for a total of eight points.

References

Other websites

 "All About Terrazzo and Terrazzo Systems,"  National Terrazzo and Mosaic Association.
 Conservation of terrazzo  on Preservapedia
"Sustainability & LEED," National Terrazzo and Mosaic Association
"LEED," Southwest Terrazzo Association
"LEED Points Possible," The Terrazzo Association of Northeastern States

Materials