Specifying Terrazzo Installations

When specifying terrazzo, it is advisable to review the information available from NTMA, which publishes industry standards and model specifications that can be customized for specific construction or renovation projects. In a standard, three-part specification format following the CSI or MasterFormat system, it is found in Division 9: Finishes under Section 09 66 23. Some of the relevant items to address are highlighted as follows.

Part 1: General

The scope of the specified work and related work as well as any definitions should be called out. It is advisable to specify a preinstallation meeting and request submittals based on the project needs, including the request for LEED documentation for credits being pursued. Quality assurance can be addressed by calling for Contractor and Associate membership in NTMA, which represents a commitment to meeting NTMA standards and protocols. Project conditions and product storage should all be addressed in typical fashion.

Part 2: Products

All of the different performance and material criteria for each of the components of a terrazzo system need to be called out. This includes the bonding matrix, primer (if required), aggregates, divider strips, and abrasive strips (for stairs if needed). If any precast terrazzo is part of the project, the types, sizes, makeups, colors, patterns, and finishes will all need to be specified. The setting materials for precast terrazzo will also need to be called out. There may be some miscellaneous accessories needed for either poured-in-place or precast terrazzo, including sealers, moisture-mitigation products, or a crack-suppression/isolation membrane. Each should be called out as required.

The details of each mix of terrazzo that is being used in the project will need to be clearly identified in the specifications and coordinated with locations as shown on the drawings. NTMA has published standard color plates and mix colors from which selections can be made. If custom colors are required, they are readily possible, but they need to be identified and specified according to the resin color and chip (aggregate) mix, showing the size, grade, and percentage of the total mix that each chip provides.

Walnut Grove Elementary School located in Bargersville, Indiana, incorporated seven bright, cheerful colors that were each specified to enhance the creative and way-finding aspects of the design.

Part 3: Execution

As with any site-installed product, the installation requires multiple steps that need to be clearly articulated in the specification in order to achieve the best results, including:

• Examination and preparation: The importance of this step should always be stressed. In addition to the architect, the installer and general contractor or construction manager should review and examine the substrate for conditions that may affect the installation or the overall performance. This can include a determination that the slab does not vary more than ¹⁄₄ inch from a true plan in a 10-foot span. It may also require the use of independent testing agencies to verify moisture content in the slab. Any issues will need to be corrected, likely by the general contractor, if they are found to be out of compliance with the stated requirements.
• Installation: For poured-in-place installations, the divider strips are installed, and the terrazzo is placed, finished, and polished as specified. For precast terrazzo, the surface is prepared, and the terrazzo is installed using the specified bonding agent.
• Protection: Once installed and finished, the surface should be able to withstand use by remaining construction personnel on the project. However, the general contractor should be instructed to cover and protect the surface as appropriate to the job-site conditions.
• Cleaning: Upon completion, the terrazzo should be cleaned of any construction or miscellaneous dirt, debris, etc. following the directions from NTMA on cleaning and maintenance.

When specified and installed correctly, the floor system will provide the desired look and long-term performance characteristics that are intended.

Conclusion

Terrazzo has been shown to provide architects, interior designers, construction professionals, and building owners/managers with an appealing, long-lasting solution for floors and other interior building surfaces. It offers exceptional design versatility with numerous options and complete customization possibilities. Its performance is well-known and documented for durability, ease of maintenance, and resistance to many conditions due to its nonporous nature. As a sustainable system, it can contribute to LEED and other green building certifications. Overall, it has been used for more than 100 years in the United States and continues to be a popular, enduring, affordable choice in both new construction and renovation.

Restaurant Renovation Case Study

Project: Gallagher’s Steak House
Location: New York City

The Project: This popular steak-house restaurant is located in the middle of the Time Square District in New York City. Established in 1927, it serves as one of the finest dining and event gatherings in New York. The building that houses Gallagher’s is timber and masonry construction with exposed floor beams that date from 100 years ago. The existing flooring is terrazzo that is finished in a checkerboard or diamond pattern that is very consistent with the overall decor and durability of this establishment.

The Challenge: Even though the beams were reinforced from the underside, the floors had sagged, and the wood joists and plywood top would deflect and bounce together under foot traffic and concentrated loading. Bouncing wood flooring is not ideal for terrazzo, especially if the ownership is very critical and does not want to see any cracking.

The Re-Flooring Solution: The nature of this building required a multistep solution. The first task was to correct the differing flooring transitions by building up an independent substrate that could act as one unit with the rest of the existing floor structure. This allowed weight applied as a single-point load to be distributed to the rest of the floor without breaking or cracking the surface.

After the floors were leveled and transitions corrected, cove base black borders around the center bar and wall perimeters were installed. The border distances from wall to wall had to be held to exact dimensions so no deviation would be visible when brass diamond-pattern strips were installed to create the diamond/checkerboard pattern.

The final step involved installing an average of 2 inches of epoxy terrazzo reinforced with ¹⁄₄-inch wire mesh to act as an independent floating slab. In some areas where the depth was not available (i.e., in the front of the existing revolving door), prefabricated pieces of terrazzo were used independently of the poured-in-place terrazzo. After completion, the installers epoxy grouted each color several times. This ensured that there were no surface pinholes to accumulate any dirt, especially in this very active restaurant and steak house.

The Design: The beauty of this floor is due to the exact mathematics of the diamond pattern. All the terrazzo diamond corners start and end precisely on the brass strip of the black border. This exact math and configuration into the floor areas is the art that is noticed right away. The visual play and design of the brass strips separating the two different terrazzo checker diamond colors is strong and appealing. The owners chose colors and a mix of terrazzo that were true to the original era to recreate the authentic look of the flooring.

The Results: Restaurant patrons have said many times that they would swear this floor always existed and compliment the management on how wonderful it looks after all those years.