Editing Terrazzo (section)

== Production ==
[[File:Pima1.jpg|thumb|Terrazzo with stylized Native-American design at the [[Hoover Dam]]]]
[[File:Gamla stan tunnelbana terrazzo 070330.JPG|thumb|Terrazzo wall at the [[Gamla stan]] metro station, [[Stockholm]]]]

Terrazzo artisans create walls, floors, [[patio]]s, 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 {{convert|3|to|4|in}} deep. After the forms are removed from the foundation, workers add a {{convert|1|in}} 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 weighted roller ({{convert|100|–|125|lb}}) over the entire surface.

In the 1970s, [[polymer]]-based terrazzo was introduced and is called thin-set terrazzo. Initially polyester and [[vinyl ester resin|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 a wider selection of colors, {{convert|1/4|to|3/8|in}} 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 for interior, not exterior, applications. Epoxy-based terrazzo will lose its color and slightly peel when used outdoors, 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 cured, helpers grind it with a [[concrete grinder|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-[[trowel]]ed for a smooth, uniform surface; it is then cleaned, polished, and sealed.<ref>{{cite web |url=http://stats.bls.gov/ooh/Construction-and-Extraction/Cement-mason-and-terrazzo-workers.htm |title=Cement Masons and Terrazzo Workers |date=29 March 2012 |work=Occupational Outlook Handbook, 2012–13 Edition |publisher=[[Bureau of Labor Statistics]], [[United States Department of Labor|U.S. Department of Labor]] |access-date=15 June 2013}}</ref>

=== Types and systems ===
[[File:Norfolk and Western Railway terrazzo logo.jpg|thumb|left|[[Norfolk and Western Railway]] terrazzo logo, Roanoke, Virginia]]
Terrazzo installation includes both bonded and unbonded methods.  Bonded systems include: bonded underbed, monolithic, chemically bonded, and the most recent, thin set method ([[epoxy]] resin). Bonded terrazzo is applied over a sand-cement mortar underbed which sits on top of a concrete slab. The sand-cement layer allows for variations in the finished concrete slab that it sits on. Monolithic terrazzo is applied directly over an extremely flat and high quality concrete sub-floor. Thin-set terrazzo does not require a concrete sub-floor. Instead, a flexible membrane can be installed so that cracks do not appear on the surface.<ref>{{Cite news|url=https://www.archtoolbox.com/materials-systems/finishes/flooringterrazzo.html|title=Flooring - Terrazzo - archtoolbox.com|work=archtoolbox.com|access-date=2017-12-05|language=en-GB}}</ref> Unbonded includes the sand cushion method which uses wire reinforcing, an isolation sheet, and sand dusting that absorbs any movement from the concrete slab.<ref name="McGraw Hill">{{cite book|title=Twentieth Century Materials: History and Conservation|last1=Jester|first1=Thomas|date=1995|publisher=McGraw Hill|location=New York|page=207}}</ref>

=== Relation to mosaics ===
Although terrazzo derives from the mosaic artform, it does not necessarily place individual pieces in a decorative pattern. Instead, small pieces are thrown into the mortar base creating a more uniform surface appearance. Decorative patterns are often created by using dividers which creates lines between different colored terrazzo mixtures.

=== Deterioration ===
Cracking is a common form of failure and is often caused by the structural system that supports the terrazzo rather than the material itself. Contact with [[alkali]]s or [[acid]]s can deteriorate the bonding agents used in terrazzo. As the aggregates are often marble dust which is [[calcium carbonate]], strong acid can also cause deterioration to the aggregates. When partial replacement is necessary, a "bracketing" system mixing and matching different chips is used to create potential matches.<ref name="McGraw Hill"/> Aged terrazzo can be resurfaced to restore its original look by re-polishing.<ref>{{Cite web|url=https://www.gsa.gov/technical-procedures/regrinding-terrazzo-floors?Form_Load=88517|title = Regrinding Terrazzo Floors| date=10 August 2016 }}</ref>