A Venetian marble mosaic, with portland cement matrix, terrazzo is composed of two parts marble chips to one part portland cement. Color pigments may be added.
Three methods of casting in place portland-cement terrazzo atop structural concrete floor slabs are commonly used: sand cushion, bonded, and monolithic.
Sand-cushion (floating) terrazzo is used where structural movement that might injure the topping is anticipated from settlement, expansion, contraction, or vibration.
This topping is at least 3 in thick. First, the underlying concrete slab is covered with a 1â„4- to 1â„2-in bed of dry sand. Over this is laid a membrane, then wire-fabric reinforcing. The terrazzo underbed is installed to 5â„8 in below the finished floor line.
Next, divider strips are placed and finally, the terrazzo topping.
Bonded terrazzo has a minimum thickness of 13â„4 in. After the underlying concrete slab has been thoroughly cleaned and soaked with water, the surface is slushed with neat portland cement to ensure a good bond with the terrazzo. Then, the underbed is laid, divider strips are installed, and terrazzo is placed.
Monolithic terrazzo is constructed by placing a 5â„8-in topping as an integral part of a green-concrete slab. Adhesive-bonded monolithic terrazzo with an epoxy resin adhesive also has been used successfully, with a topping thickness of only 3â„8 in.
Terrazzo may be precast. It generally is used in this form for treads, risers, platforms, and stringers on stairs.
Because of the large variety of color and surface textures that can be attained with terrazzo, it is used extensively as an exterior and interior decorative flooring.
Portland-cement terrazzo, however, should not be used in areas subject to spillage, such as might be encountered in kitchens.
Details on selecting the proper type of terrazzo, marble-chip sizes, methods of applying, and finishing of the surface may be obtained from the National Terrazzo and Mosaic Association, 110 Market Street, Suite 200A, Leesburg, VA 20176. Also, specification sheets for terrazzo are published by the American Institute of Architects.
Other matrix materials used with marble chips include rubber latex, epoxy, and polyesters. Suppliers should be consulted for installation details.
