Minimize demolition and optimize durability
Sponsored by National Terrazzo & Mosaic Association
By Peter J. Arsenault, FAIA, NCARB, LEED AP
It has been said that the greenest building is an exsisting one. This logic proves true when the strategy is to reduce the environmental impact of building materials and construction by using what is already exsisting. A specific strategy is to consider the use of new flooring in a renovation project that does not require the selective demolition and removal of existing flooring. Of course, to be truly sustainable, the new flooring needs to be durable and resilient for a long service life. It would also need to be versatile with abundant design options, patterns, and colors available and the ability to be used on other surfaces too. On elevated floors, it would help if it were lightweight so as not to for green building design. While this may sound like a difficult list of needs to fulfill, there is a very well-known and readily available flooring that meets all these criteria: epoxy terrazzo. In this course, we address these aspects of using terrazzo flooring as a cost-effective, sustainable flooring in existing buildings.
TERRAZZO: A PROVEN SOLUTION
Many architects and interior designers are familiar with terrazzo as used in contemporary and historic buildings. However, not all are aware of its history, current formulations, and sustainable or green building attributes, which are summarized as follows.
The use of terrazzo for flooring and wall surfaces has been common for centuries. Some would trace it back to ancient Egypt, where mosaic flooring was held in place with cementitious binders. The more recent version of the material is influenced by 18th century Italian craftsmen who placed marble fragments in a mortar base or spread marble chips into cement that was then ground and polished. Terrazzo made its way to the United States in the 1890s and became popular in the 1920s for its noted strength and durability as a flooring treatment.
Beginning in 1924, the use of divider strips offered greater control over cracking, which was sometimes a problem without their use. The divider strips also allowed for different colors or textures of terrazzo to be separated, making it possible to design virtually any shape, pattern, or image into the surface. Around the same time, electric grinding machines became available, replacing the need to grind and polish the terrazzo surface by hand. The mechanization of the entire process meant that the costs and time associated with terrazzo were both notably reduced, making it a more affordable flooring option for many commercial and institutional buildings.
With great design versatility, solid durability, and increased affordability, the use of terrazzo increased, as did the number of companies and craftspeople dedicated to the trade. This prompted the formation, in 1923, of the National Terrazzo and Mosaic Organization (NTMA). As a full-service, non-profit trade association headquartered in Fredericksburg, Texas, NTMA has established national standards for all terrazzo floor and wall systems. It currently provides complete specifications, color plates, and general information to both architects and designers at no cost.
Current Formulations
Fundamentally, terrazzo is a composite system consisting of either a cement or resinous matrix (binder) with aggregates added that can be made of marble, granite, onyx, or glass. Terrazzo is most commonly poured in place, cured, and ground to a smooth, hard surface finish. There are also precast terrazzo products available that can be installed like tiles or used to form stair treads and risers. As such, it is commonly used for flooring, stairs, and even corridor walls whenever durable, easy-to-clean, and attractive surfaces are being sought.
There are multiple variations on the way that terrazzo is formulated and installed:
Epoxy terrazzo: This is a nominal ¼-inch-thick or 3⁄8-inch-thick resin matrix veneer placed on a flat concrete slab provided by others. It can be specified with glass, synthetic, or granite aggregates in lieu of marble to provide brilliant colors or chemical resistance. Recognized as the best thin-set system, it accounts for approximately 95 percent of all the terrazzo installed today. It offers unlimited matrix colors, color control, resiliency, chemical resistance, and tensile-compressive strengths not found in cement-based systems. It is excellent for multicolored patterns and designs. Epoxy terrazzo is lightweight (approximately 4½ PSF for 3⁄8-inch thickness) and somewhat flexible, making it ideal for multistory use. It has the lowest maintenance cost due to its nonabsorbency. In sanitary areas, it can be installed with minimal dividers, providing seamless characteristics. When used in conjunction with a flexible membrane as a specified extra, it can absorb some horizontal concrete crack or control joint movement. From an installation standpoint, it has the quickest pour-to grind installation time. It can be used over a variety of properly installed and prepared substrates including plywood.
Polyacrylate terrazzo: A nominal 3⁄8-inch-think polymer modified cement matrix veneer is placed upon a flat concrete slab provided by others. The polyacrylate polymer provides strength to allow for thinner applications of cementitious systems. It provides fast installation and moderate price range, making it ideal to replace vinyl or carpet without depth transition difficulties. It is also good to use in areas subject to moisture vapor transmission, where epoxy terrazzo or other non-breathing floors require additional steps to make them applicable.
Monolithic terrazzo: This is a ½-inch thick cement matrix veneer placed upon a concrete slab provided by others. It is dependent on the concrete quality for flatness and crack prevention. It is appropriate for on grade or below grade. Its fast installation and economical price make it ideal where time and budget are critical but the beauty, low maintenance, and performance of terrazzo are desired.
Bonded terrazzo: This is a cement matrix and underbed system used for interior and exterior areas. It is meant for conditions that require 1¼ inches to 1¾ inches of recessed depth to be filled in addition to the ½-inch terrazzo topping. With the sand-cement underbed, it has less dependence on the concrete slab for flatness when compared to monolithic.
Sand-cushion terrazzo: A ½-inch cement matrix topping is used with a 2½-inch to 3-inch underbed of low-slump sand cement. The complete system includes wire reinforcing, an isolation sheet, and a sand-dusting layer over a new or existing concrete slab. This is considered the best cement system and is intended for interior use. Due to the underbed’s depth, wire mesh reinforcing, isolation sheeting, and sand layer, it will absorb minor substrate defects and prevent mirroring to the surface.
Rustic terrazzo: This is a terrazzo produced with a non-ground, textured surface intended for exterior use. This system is available with bonded and monolithic terrazzo. It offers infinitely variable textures, colors, and patterns that may be created in a weather-resistant, skid-resistant deck surface.
Note that in any of these terrazzo formulations, the aggregate chip sizes used can be selected to suit the intended design appearance. The sizes are only limited by the thickness of the terrazzo, such that chips can be #0 or #1 in ¼-inch terrazzo with the option of #2 in 3⁄8-inch terrazzo. As mentioned, marble, granite, or other stone is the most common type of such chips, but others are possible. However, note that glass and other decorative aggregates do increase costs.
Sustainability
Terrazzo is a sustainable option for many reasons, including the following:
• Natural materials: The aggregates are natural stone materials that can be responsibly sourced.
• Resin matrix: As an alternative to a cement matrix, epoxy (resin) terrazzo does not have the same embodied energy.
• Long life cycle: Terrazzo is a long-lasting and durable material that holds up to heavy foot traffic and other intense uses.
• Wellness: Terrazzo is nonporous and does not support microbial growth, nor does it allow moisture to accumulate, contributing to a mold-free, healthy environment. Additionally, terrazzo is comprised of little to no volatile organic compound (VOC) materials, and it exhibits little to no off-gassing over the life of the cured material.
• Ease of maintenance: As a very low-maintenance system, terrazzo can be cleaned with an environmentally friendly, neutral pH cleaner. This reduces or eliminates the need for harsh chemicals or cleaners that can irritate sensitive eyes or noses.
DESIGN AND PERFORMANCE CONSIDERATIONS
When considering the use of terrazzo for a sustainable building design, there are several key factors to recognize and keep in mind regarding both design and performance capabilities.
Design Versatility
Perhaps most appealing to many architects and interior designers is the versatility of terrazzo. The custom nature of terrazzo installations means that designs of all types, patterns, and colors can be incorporated into flooring, walls, stairs, platforms, balconies, countertops, walls, columns, or other surfaces. For example, imagery such as logos, government seals, mascots, maps, historical events, scientific facts, numbers, or other purposeful information can be displayed in the floor or walls of a lobby or public space. In large facilities, way-finding information can become part of the terrazzo design to help building users and visitors become oriented and find specific areas of a building. In other cases, a simple pattern can be used to create a subtle background for a space or for some featured coloring along a corridor or other circulation space. In short, the vast color, shape, pattern, and design options provide great freedom to create spaces that can meet virtually any design intent.
Performance
While some flooring and surface treatments might look good when first installed, their long-term performance may be lacking. Terrazzo, on the other hand, is well-known for its ability to hold up and continue looking great over the long term. In fact, there are numerous historic buildings that contain the original terrazzo flooring, which is still very successfully in use. In Oregon, for example, Portland’s Pioneer Courthouse boasts terrazzo floors dating from 1905. Further, terrazzo has been documented numerous times to withstand not only normal wear and tear but also dramatic events such as floods and hurricanes as well.
Among the many factors that contribute to the impressive performance of terrazzo are the following:
Inherent strength: While it may be considered lightweight (3⁄8-inch epoxy terrazzo weighs approximately 4½ pounds per square foot), the aggregates and matrix binders are inherently strong materials. Terrazzo has been shown repeatedly that it can readily hold up to heavy foot traffic or other demands.
Low maintenance: While regular cleaning is needed for any floor, the nonabsorbent surface keeps dirt and debris on top while resisting staining.
Sanitary: In spaces where sanitary conditions are needed, the nonabsorbent surface also contributes to the ongoing likelihood of meeting these conditions.
Epoxy enhancements: When epoxy terrazzo is used, color control, resiliency, chemical resistance, and tensile-compressive strengths are all increased compared with cement-based systems.
Beyond the basic materials of the terrazzo, metal dividers are used for both design and performance reasons. As already noted, dividers can be set to separate colors or as an accent themselves. In these cases, the dividers are strictly decorative and related to the concrete slab or joints below it.
Beyond the decorative aspect, dividers are primarily used to maintain the integrity of the terrazzo over concrete. Their proper use and placement help overcome any potential cracking in the terrazzo. This is because terrazzo by itself is not likely to crack but can be impacted by the concrete substrate below it that, if it cracks, can telegraph up into the terrazzo surface. Therefore, the following should be kept in mind regarding the dividers:
Concrete standard: To reduce the potential for cracking and therefore the terrazzo, ACI 302.1 R.89: Concrete Joint Placement must be followed. Location of dividers: Most systems adhere to the concrete and require dividers to be placed precisely above any concrete joints.
Divider materials: Zinc and aluminum are standard, but brass and colored plastic are readily available.
Size: Dividers vary in width from 18 gauge to ½ inch with 16 gauge or 1⁄8 inch as common standard sizes.
Minimizing: In sanitary areas, terrazzo can be installed with minimal dividers, providing seamless characteristics.
Note that when dividers are used in conjunction with a flexible membrane as a specified extra, terrazzo can absorb some horizontal concrete crack or control joint movement. However, it is important to recognize that dividers do not function as leveling devices or crack preventers. Further, architects should design structural inset expansion plates between areas where major movement is anticipated.
Managing Cost
All building projects involve a discussion of costs, so it is important to understand that the cost of terrazzo is manageable and controllable by recognizing some of the influencing factors.
Design: Cost is often controlled by design—a simple pattern in one or two colors costs less than multiple colors throughout or fully custom designs. Therefore, it is a common tactic to keep designs simple in corridors, walkways, etc. and put a feature or custom image in a lobby or other central area.
First cost: The first cost of terrazzo is generally comparable to other commercial flooring options.
Installation time: Epoxy terrazzo has the quickest installation time between pouring and grinding. While cement systems take a week or more for curing, epoxy is usually about half that time. It cures in 24 hours or less and can be walked on by other trades, etc. at room temperature. Finish work (i.e., grinding and polishing) follows the curing.
Aggregate choice: Stone aggregates are standard, but glass and other decorative aggregates can increase costs.
Maintenance costs: The maintenance costs of epoxy terrazzo are typically the lowest compared to other flooring due to its non-absorbency. The smooth, polished surfaces allow for use of simplified cleaning, including automated or robotic cleaning. Further, mold is not supported, thus removing this otherwise common maintenance concern.
RENOVATION DESIGN WITH TERRAZZO
Terrazzo is appealing for new construction and readily incorporated, but there are many existing buildings that can benefit from renovation with terrazzo too. Keep in mind that renovation can mean renovating the entire building or renovating the existing terrazzo too.
Renovating Existing Terrazzo
Properly maintained existing terrazzo will likely last the life of the building. However, sometimes it needs some refreshing, perhaps due to neglected maintenance, changes in building use, or new interior designs or layouts. In these cases, it is fairly simple to make existing terrazzo flooring look like new for very little cost. Fundamentally, the process involves the repair and repolishing of the existing surface. This can restore the shine, bring back the original colors, and make it easier to maintain going forward.
Renovating Buildings with New Terrazzo
Existing buildings are a prime candidate for cost-effective flooring upgrades using terrazzo. Contrary to what some design professionals may think though, new installations over existing flooring do not always require the existing flooring to be demolished or removed. In some cases, with a proper assessment, the existing flooring can be determined to be sound and secure enough to remain in place, perhaps requiring only spot repairs where needed. As such, it can serve as the substrate for a terrazzo installation, thus saving dramatically on project costs. Demolition, removal, and disposal of the existing floor may be avoided, saving considerable time and expense.
What types of flooring are appropriate? NTMA has provided guidance for very successful installations over quarry tile, polished concrete, ordinary concrete, and even hardwood flooring. It certain cases, it can also be used over properly installed and prepared plywood. Of course, it is not suitable to go over soft goods, such as vinyl tile, sheet goods, carpet, etc. Note that some porcelain tile is too smooth to create a bond with the terrazzo, and the prep work will likely damage the tile and break it, so it may need to be removed.
Regardless of the type of existing flooring, the prep work is very important before installation. The substrate needs to be clean and solid with a profiled surface so an adequate bond can happen between the terrazzo and the existing floor. The floor needs to be fully assessed to be sure it is free of damage and is still structurally sound. If not, it will need to be repaired, removed, or replaced as required.
As with all flooring, moisture needs to be addressed, particularly on a concrete slab. There is typically no problem with moisture if cement terrazzo is being used. Epoxy terrazzo can be a concern since it can trap moisture or compromise the bond between the terrazzo and substrate. Therefore, some mitigation is required. The best solution is to provide a low-permeability moisture-control layer as a first coat over the existing substrate. This step helps to control vapor transmission so there is no loss of bond between the terrazzo and the existing flooring.
GREEN BUILDING CONTRIBUTIONS OF TERRAZZO
When terrazzo is incorporated into a building design or renovation, there are several contributions that may be made using LEED v.4 criteria due to its inherent properties and characteristics. These include the following.
Optimizing Energy Use
Energy performance in a building is often enhanced by adding thermal mass within the building envelope. Terrazzo over concrete can provide some additional thermal mass inside a building. As such, it may help with heating and cooling optimization and energy-usage calculations.
Materials and Resources
When looking at a life cycle-assessment (LCA) for a building, several traits of terrazzo help produce very favorable results. First, is its basic material makeup. The epoxy resin is based on 100 percent solid materials that do not contain portland cement. Avoiding the embodied energy in lime-rich cements is a direct strategy to reduce the environmental impact of materials. Regarding the aggregates, we have noted that they can be natural stone or recycled glass, both of which can have reduced environmental impacts, particularly if they are sourced local to the project site. Finally, the longevity and durability of the material means that it will likely not need to be replaced during the life of the building in contrast to other flooring materials that would likely need to be replaced repeatedly.
Indoor Environmental Quality
As a natural and tested material, terrazzo exhibits very favorable traits for indoor environments. There is little to no outgassing before, during, or after installation. No formaldehyde is present in the formulations, and VOCs are little to none. No paints, coatings, adhesives, or harmful sealants are needed. Perhaps most telling in terms of minimal indoor impacts, terrazzo installations often occur when buildings are still occupied with no adverse effects on occupants.
Overall, terrazzo is an excellent choice with documented capabilities to be able to contribute to LEED certifications.
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.
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 ¼ 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.