The Beauty of Designing Sustainable Terrazzo Flooring

Aspects of Terrazzo Flooring
Terrazzo floors have been around for centuries and have been the original recycled flooring, as they used marble chips that were a by-product of the stone-cutting trades. Today technology and green design have pushed terrazzo back into the spotlight. Terrazzo is "green" in its durability, composition, recycled content, and air quality issues.

Durability
Sustainable construction is the core of green building. Terrazzo floors typically will last the lifetime of the structure. In many older buildings, floors can be restored to their original luster at a fraction of the cost of replacing the floor. Both cement and thin set epoxy floors have extremely low maintenance costs. Periodic stripping and resealing can use environmentally friendly water-based products. Routine maintenance includes dry and damp mopping, with an occasional spray buffing. Generally maintenance for terrazzo is significantly less than tile with its numerous grout lines and carpet and energy-intensive vacuuming and steam cleaning.
 
Composition and Embodied Energy
Terrazzo is composed of natural occurring aggregates, recycled glass, plastic, or oyster shell, and a processed cement or epoxy binder. The binder consists of 30 percent of the volume of the terrazzo. Initial life-cycle assessments of embodied energy appear favorable due to the longevity of the floor and its low energy use for maintenance.

Recycle/Reuse content
Glass aggregates are available from several suppliers in a variety of forms - from 100-percent post-consumer glass (bottles used by the consumer and collected in a recycling program) to 98-percent industrial glass (generally scrap window applications; this is melted and colored). Often post-industrial glass has no other recycling market. Some stone aggregates are reclaimed from prior uses to be made into aggregates for the terrazzo market. Plastic aggregates may contain up to 20-percent recycled content, and a recycled metal divider strip can be incorporated. Twenty-percent recycled content may be achieved by using recycled glass fillers (sizes not generally visable). A flooring finish can incorporate glass aggregates and glass fillers in a recycled content of 70 percent.

VOC Off-gassing/Indoor Air Quality
Both cement and epoxy matrix floor systems are comprised of zero volatile organic compounds (VOC) materials. Terrazzo exhibits little or no off-gassing over the life of the cured floor. The nonporous, cleanable terrazzo finish does not support microbial growth, nor allows moisture to accumulate, helping to maintain a mold-free environment and improved indoor air quality.

Designing Terrazzo Flooring
First, let's define what terrazzo means and identify applications.

The National Terrazzo and Mosaic Association (NTMA) defines terrazzo as follows: "Terrazzo consists of marble, granite, onyx, or glass chips in Portland Cement, polyacrylate Portland Cement, or resinous matrix binder. The terrazzo is poured, cured, ground, and polished. Terrazzo is typically used as finish for floors, stairs, or walls."

Terrazzo is used as both an interior and exterior finish. Portland Cement and polyacrylate matrix terrazzo can be used for both interior and exterior applications. Epoxy resin matrix terrazzo, however, is not recommended for exterior use. Also, a style of terrazzo known as rustic terrazzo is frequently used for outdoor applications; it has a rough surface for added slip resistance.

When considering which terrazzo system is best suited for the proposed application, the required thickness may become the deciding factor. The following minimum thickness and weight apply for each respective terrazzo system:

Exterior sand cushion/Venetian terrazzo ................. 2½ inch; 30 lbs/sq. ft.
Exterior bonded .................................................... 2 inch; 20 lbs/sq. ft.
Interior/exterior polyacrylate ................................... ½ inch; 3 lbs/sq. ft.
Interior epoxy resin terrazzo ................................... 3/8 inch; 3 lbs/sq. ft.

Advantages/Limitations of Terrazzo Types:

• Can be used in both interior and exterior applications
• Can be acid-washed for added slip resistance for exterior use
• Topping thickness will accommodate the largest chip size
• System is breathable and not affected by moisture vapor transmission
• Sand cushion terrazzo can accommodate substrate defects

Limitations

• Requires minimum 2½-inch depression for system installation
• Vibrant colors are limited in Portland Cement
• Glass chips are not recommended in unmodified cement
• Additives must be used to overcome alkali silica reaction between glass and cement
• Design flexibility due to panel size limitations
• Lengthy cure times to achieve final appearance

• System thickness of ½ inch total; can be used over a wood substrate
• Glass chips can be used in polyacrylate matrix terrazzo
• Can be used in outdoor applications
• System is breathable and not affected by moisture vapor transmission
• Can be acid-washed for exterior nonslip applications

Limitations

• ½ inch total thickness requires high flatness tolerance of ¼ inch per 10 square feet in the substrate
• Vibrant colors cannot be achieved in a polyacrylate matrix
• Maximum chip size that can be used is a #2

• System thickness of 3/8 inch total can be used over concrete or wood subspace
• Virtually unlimited range of vibrant colors available
• Glass chips can be used in epoxy resin terrazzo
• Design flexibility due to minimal divider strip requirements
• Accelerated chemical cure allows for faster installation
• Good color uniformity on large installations due to sophisticated manufacturing process for epoxy resin
• Most cost-effective terrazzo system for interior use

Limitations

• 3/8 inch thickness requires a high flatness tolerance of ¼ inch per 10 square feet of substrate
• Not recommended for exterior use
• System not breathable; effective moisture vapor barrier required for slab-on-grade applications
• Maximum chip size that can be used #2

Matrix Design and Products
The terrazzo matrix binder allows virtually any color of terrazzo to be produced. While there is a wide range of marble and glass colors, virtually any color may be produced with epoxy resin matrix terrazzo. A limited variety of colors can also be produced with Portland Cement and polyacrylate matrixes.

Matrix design can become even more detailed with the introduction of aggregates and strip dividers for artistic creation. Excellent quality domestic and imported marble chips are available for use in terrazzo in a wide range of colors. Colored glass chips can complement any marble design. Other products such as mother of pearl and metal chips can be used in epoxy terrazzo matrixes.

By selecting various terrazzo chip sizing you may alter the look even more. Terrazzo chips are available in sizes ranging from 1/16 inch up to 1 inch (See Sizing Chart).

In addition, divider strips are used in terrazzo for both function and aesthetics. Divider strips act as control joints, for transitions between matrix colors and from vertical to horizontal installations and for termination to adjacent flooring finishes. Divider strips are commonly used aesthetically to create custom designs and patterns in the terrazzo. Intricate logo artwork and lettering can be created with water jet designs. Strips are available in both zinc and brass.

Sustainability of Terrazzo
Have you walked across a newly constructed airport floor and noticed the beauty, design, and possibilities of a terrazzo floor? Today's terrazzo floors have more color possibilities, more selection of aggregates, and more design potential than ever before. Terrazzo floors are beautifying homes, hospitals, shopping centers, schools, and restaurants. The versatile color and design can go from bold and bright to the elegant and classic styles. Terrazzo floors can be personalized in design to depict anything from local attractions to sport heroes, from one simple colored floor to complex geometric shapes. Terrazzo floors, along with their beauty, have a history of durability in high-traffic areas and are easy to maintain.

In addition to these historic values, current trends now favor the added bonus of containing up to 70-percent recycled material, which helps contribute to five different point areas in the United States Green Building Council's (USGBC's) LEED rating system.

Terrazzo is a composition of a cement or epoxy that can contain a combination of marble, glass, shell, or other types of decorative aggregates. It is troweled in place, ground, and brought to a polish. The grinding process reveals a floor that is 30-percent cement or epoxy and 70-percent aggregate, giving the floor its characteristic speckled appearance. It is customary for the epoxy or cement to be tinted.

Aggregates are selected from a variety of sizes, colors, and transparencies. Small metal strips divide color, provide for expansion and contraction, and transition between terrazzo and other surfaces.

A terrazzo floor can keep its newly laid luster for 40 years or more with a periodic dust mopping and weekly buffing. It has less maintenance requirements than the daily vacuuming of carpet or grout cleaning of tile.

Terrazzo comes in three categories: cement, polyacrylate, and epoxy.

Cement
Cement is the oldest of the three types of terrazzo and has the advantage of both interior and exterior application. It will accommodate the largest chip size, is breathable, and can cover up subfloor defects. It can be acid-washed for exterior nonslip surfaces. Cement has the most limitations: It requires a 2½-inch allowance for installation, color choices are limited, glass chips are not recommended, and divider strips are placed closer together, limiting design flexibility. It also requires lengthy cure times.

Polyacrylate
Polyacrylate is a modified cement system using an acrylic additive that allows the cement to be poured as thin as ½ inch thick. Other advantages include its use in outdoor applications because it is breathable; glass chips can be used; and it can also be acid-washed for outdoor applications. Because of its ½ inch thickness it requires a high flatness tolerance for the subfloor. Vibrant colors cannot be achieved, and it is limited to a smaller chip size.

Epoxy
Epoxy terrazzo is the thinnest of the three systems at 3/8 inch. It has virtually an unlimited range of vibrant colors because of the ability for the epoxy to accept color. Glass chips can be used. Accelerated installation can occur because of the epoxy's rapid cure time. There is greater design flexibility because of minimal expansion divider strip requirements. It has the lowest cost for interior use. Its 3/8 inch thickness requires a high flatness tolerance. It is not recommended for exterior use because it is not a breathable system. Smaller chips will be required because of its 3/8 inch thickness.

One of the exciting new materials available in aggregates for terrazzo flooring is glass. Glass gives terrazzo floors a transparency and depth that has not been available in marble. Glass is all about color - from intense red to deep blues to soft greens and crystal clear. Crushed mirror can add reflective sparkle, and silver-coated glass can put a reflective backing on any of the colors. Glass can match any envisioned design and add brilliance to otherwise mundane flooring.

Post-consumer glass allows bottles that were used for weeks to have a new life in a terrazzo floor and used possibly for the rest of the life of the building. Post-industrial glass - scrap glass from window manufacturing - is melted and colored to be made into aggregates for the terrazzo market. Often post-industrial glass has no other recycling market. Glass filler, 16 mesh and smaller, can be used to achieve 20-percent recycled content. If filler is combined with glass aggregates, the percentage of recycled content in the terrazzo finish could be up to 70 percent.

With the increasing interest in green building, a glass terrazzo floor offers an eco-friendly option. The durability and low maintenance of a terrazzo floor ensures use and enjoyment for years to come. Few other floorings can boast of the advantages of a terrazzo floor. Its design can be as limitless as the creative process. 

Ken Thornley ([email protected]) is vice president at Heritage Glass Inc. He has spent 28 years working with glass and glass coloring. He introduced glass aggregates to the terrazzo floor market in the mid-1980s and is an active member of the National Terrazzo and Mosaic Association (NTMA) and the U.S. Green Building Association (USGBA).

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