Terrazzo is a composite flooring system consisting of either a cement or resinous binder/matrix mixed with chips of marble, glass, and/or a variety of other aggregates. It’s usually mixed on-site and troweled in place, then cured, ground, and polished to a smooth, hard finish. Terrazzo is one of the most beautiful, durable, and sustainable floor finishes available. Terrazzo floors can range from a single color with monochromatic chips to varied combinations of colors and patterns. Many designers and architects specify terrazzo because it holds unlimited design possibilities. Design features like company logos, school mascots, artwork, and wayfinding can easily be incorporated into terrazzo.
Terrazzo can be classified into 2 broad categories based on its type of binder: cementitious and resinous. Originally, terrazzo was a cementitious material, and from the 16th century until today, cement terrazzo has provided a beautiful and durable floor finish. There have been many innovations in cementitious terrazzo, and today it takes a variety of forms. Examples of cement terrazzo systems are:
Resinous binders for terrazzo were developed in the United States in the 1960s, and these systems are credited with sparking a renewed interest in terrazzo due to their ability to overcome certain design limitations like color and thickness. In contemporary construction, epoxy terrazzo dominates the terrazzo market.
Examples of resinous terrazzo systems are:
In addition to the traditional categories of cement and resinous, in recent years, manufacturers of flooring materials and decorative concrete toppings have been developing proprietary systems using cement binders that have been modified to deliver a thinner profile than traditional cement systems, accept a wider range of pigments, and in some cases, are flowable rather than trowel applied.
While each terrazzo application is unique, a terrazzo floor is generally made up of individual components that work together to create the assembly:
One or more types of membranes may be required over the substrate prior to the terrazzo being placed. Generally, the purpose of a membrane is to prepare the substrate for the terrazzo topping in some way. For example, if the terrazzo is an unbonded system, a cleavage membrane may be used to separate the terrazzo assembly from the substrate, allowing them to move independently. Alternatively, if the terrazzo is a bonded system, there may be a primer over the substrate that acts as a bonding agent for the terrazzo topping. A moisture mitigation membrane may be specified if the substrate is found to contain excess moisture or relative humidity. A crack suppression membrane may be specified to prevent small cracks from telegraphing from the substrate to the terrazzo finish.
The binder, sometimes called the matrix, is a cementitious or resinous mixture that suspends the aggregate. Aggregate is typically mechanically mixed with the binder, resulting in a stiff mixture which is troweled onto the floor. Under some circumstances, the binder may be mixed and placed onto the substrate prior to the aggregate, which is then handbroadcast. After the rough grinding process, the binder may be hand-troweled to fill small voids that might occur; this is known as grouting the floor. Cementitious binders come from white or grey cement and can be pigmented to a variety of neutral colors; epoxy binders can be colored to any custom color. A terrazzo design may call for a single color binder, or many colors separated by divider strips.
The aggregate, sometimes called chips, gives a terrazzo floor most of its visual impact, as designs typically call for 75-85% chip density. Common types of aggregate include marble, granite, and river rock. Colored glass, crushed mirror, mother-of-pearl (seashells), and other materials may also be used if they are compatible with the binder. The size of aggregates vary and are specified according to the size screen the chips pass through. A terrazzo design may call for a single material, single size aggregate, or it may combine aggregates of many types and sizes in the mix. Larger aggregates may require a greater overall thickness of the assembly. Many creative applications can be achieved by specialty aggregates, such as Venetian terrazzo (aggregates ranging from #1 to #5) and Palladiana terrazzo (stone, glass, or tile mosaics inlaid into the floor with terrazzo poured around them)
Divider strips serve aesthetic and functional purposes: they divide areas of terrazzo into smaller modules that may receive contrasting colors of terrazzo; they provide opportunity for creative designs like logos, mascots, and other artwork; and they can provide accommodation for movement within larger floor areas. The strips may be made of zinc, brass, aluminum, or plastic. They come in widths from 16 gauge to 1/2 in., with the most common width being 16 gauge or 1/8 in. The strips also come in various heights and are ground flush when the floor is ground and polished. Terrazzo divider strips are not flattening or leveling devices. They must adhere tightly to the substrate.
To protect the finished floor, an initial sealer compatible with the terrazzo is applied after the final polish. Sealers can be water-based, and many contain a blend of acrylic polymers that provide a stain-resistant surface seal and a temporary high-gloss finish. As with any finish, a regular maintenance program is recommended to prolong the life of the floor.
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