Terrazzo is derived from the marble mosaic tradition and used for finishing floors, walls, stairs, and more. Historically, terrazzo was a combination of aggregates (often decorative and colorful, referred to as stone chips) within a cementitious matrix, which was laid wet and when cured, ground to a smooth finish. Terrazzo gained popularity in the 20th century because it’s durable, sanitary, low-maintenance, and has a breadth of aesthetic capabilities. Two early 20th century technical innovations increased its popularity and use: the invention of brass divider strips to control cracking, and invention of the electric grinding machine, which makes terrazzo cost-effective.
Historic terrazzo installation methods are Monolithic, Bonded, and Sand-Cushion Terrazzo. Historic topping types are Standard, Venetian, and Palladiana. The topping is typically 1/4 to 7/8 inches thick, consisting of approximately 70% stone chips embedded in 30% cement matrix, that’s left in a rustic state, ground flat, or polished smooth. Pigments are sometimes added to change the matrix color.
Terrazzo systems are either bonded to the concrete floor slab or unbonded and separated using sand and paper. Bonded systems have a greater tendency to crack due to restraint, thermal movement, and vibration in the floor slab. Brass, copper, or zinc strips are installed over beams and girders, and parallel with columns and walls, dividing the expanse into sections to control cracking.
Prior to repairing, replacing, or restoring existing terrazzo, sources of deterioration should be addressed and mitigated. Refer to our restoration best practices page for additional information, details, and resources. Below, find terrazzo repair and restoration options for consideration on your project.
Cementitious terrazzo that’s severely cracked, spalled, eroded, or damaged is commonly replaced during restoration projects and not repaired. Replacement of sections between divider strips or wholesale replacement need to be determined based on the level of damage. In some cases, it’s appropriate to replace cementitious terrazzo with an epoxy terrazzo system. This alternative system replaces the cementitious matrix with an epoxy-based matrix. Refer to our new terrazzo page for additional information on this system.
New terrazzo should generally be replaced to mimic the existing system. Terrazzo was typically poured-in-place onsite, or pre-cast offsite and later installed. For poured-in-place floor installation, concrete slab preparation, underbed, and metal divider strips would be installed. For wall installation, metal lathe, scratch coat, and mortar underbed and metal divider strips would be installed. Once the terrazzo mix was placed and cured, the surface would be successively ground smooth. A slurry coat of portland cement would be applied to fill pin holes, and ground smooth after. Stair treads, risers, stringers, wall base, and plinth blocks were often precast. After installation is complete, the floor would be gently cleaned and sealed.
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Here are some additional resources that focus on terrazzo repair and restoration. For a more comprehensive list of repair and restoration resources, please refer to the restoration page. For additional guidance, contact IMI.
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