What do you get when you cross an artist with a concrete contractor? It’s no joke; you get great decorative concrete surfaces (floors and pavements). Through the use of stains, stamps, dyes, colored pigments, white cement, textured patterns, ornate sawcuts, epoxy overlay, and more, concrete floors are becoming increasingly attractive for home and facility owners. As techniques for decorative concrete finishes are developed, other decorative floor coverings are being replaced by concrete.
Concrete floors provide an alternative to moisture-sensitive flooring materials. Using concrete as the exposed finish offers several benefits. With fast construction schedules, concrete may not have time to dry adequately prior to placing an adhered finish. If that finish is impermeable or is applied with moisture-sensitive glue, there is a potential for failure: debonding, delamination, blistering, and expansion are a few problems associated with moisture in floors. Read more on concrete floors and moisture.
For both interior and exterior applications, varying looks are achieved by employing one or more of these techniques. This page provides a sampling of some of the available techniques for adding visual interest to a concrete surface.
One of the most popular and enduring decorative concrete finishes, exposed aggregate uses the texture of the rock or stone in the concrete to embellish the surface. In this technique, concrete is placed and floated as normal. The concrete is left to set and the surface paste is later removed by washing and/or brushing. In a variation of the method, select aggregate is cast over the fresh surface and embedded prior to setting of the concrete. Washing and brushing follow as before to remove the mortar from the surface, fully exposing the natural color and texture of the aggregate. An acid wash may also be performed to further remove paste from the aggregate and brighten the surface. Read more on exposed aggregates in concrete.
Stamping, which can be used for both interior and exterior concrete surfaces, has literally made a big impression over the last several decades. Stamped surfaces are created by supplementing finishing operations on fresh concrete with patterned or textured mats and templates. Having started as simple shapes and minimal textures, stamping tools and techniques have continually evolved to an advanced stage. Truly realistic textures can be enhanced with color additions, mimicking natural stone, rock, wood, brick, and more. The only limitation is the designer’s imagination.
Standard procedures for placing, finishing, and curing concrete flatwork apply – with a few added steps. Using a stamping tool or pattern, fresh concrete is imprinted after the initial float pass and application of a release agent. If color is to be used, a dry shake color harder may be applied during finishing. The stamping procedure effectively replaces steel troweling, and the effect is a unique surface in both pattern and texture.
One way to reduce the cost of materials for colored flatwork finishes is to place the color only at or near the surface. There are two common approaches for doing this: Dry-shake finishes or the two-course method. Both are compatible with stamped finishing techniques. Read more on decorative concrete.
Integral Colors, Staining, Tinting, and Dying
There are many ways to color concrete—before it has hardened or afterwards. Integral pigments are mixed into fresh concrete to create through-body color. Alternately, stains, tints, or dyes can be applied to hardened surfaces to impart color. Chemical stains react with hardened concrete to become an integral component of the floor surface. Pigmented tints or dyes deposit finely ground pigments into the substrate. To allow for the greatest range of colors, including pastels and deep, vibrant hues, white portland cement provides a neutral tinting base for adding color. Alternately, it enables bright white finishes when used in combination with white aggregates.
Logos and other creative designs made from a combination of stains and dyes accentuate the lobby of a commercial building
Stains enhance the inherent irregularities in the concrete surface with color to resemble a marble appearance.
Chemically reactive stains are water-based, acidic solutions that contain metallic salts. These metallic salts react chemically with calcium hydroxide compounds (hydrated lime) in hardened concrete. Such reactions form the insoluble colors that become a permanent fixture of the hardened concrete surface.
Partly due to the irregularity in finishing patterns and partly due to the inherent variation of the concrete materials, stain chemicals react in a very irregular pattern – giving it a decorative effect. As a result, mix constituents and finishing techniques will greatly influence how effective the staining can be. Controlling these parameters is important for achieving the best effect from the stain.
Stains can be applied to old or new concrete; to colored or gray surfaces; and may be used in conjunction with other decorative techniques and creative joint patterns. Combining chemical stains with dyes presents an unlimited palette of colors to create floor patterns and designs. To protect and enhance the color of the floor, using a sealer is an important step. However, just as material selection for the concrete is important, selection of the appropriate sealer is also important for the performance and durability of the floor.
Sawcut joints are installed using either an early-entry saw after concrete finishing or a conventional saw after concrete setting. Alternately, jointing tools (rather than saws) can add pattern lines to fresh concrete surfaces. Since joints should be used to control concrete cracking anyway, this is a simple—and purposeful—method for adding greater interest to concrete surfaces. Read more on joints.
This concrete slab at the Kennedy Space Center in Melbourne, Florida, uses creative sawcut joints to enhance the outer space ambiance of the facility.
According to the National Terrazzo and Mosaic Association, terrazzo was originally created in Italy over 1,500 hundred years ago by Venetian workers searching for a way to use discarded marble remnants – making it one of the world’s first green flooring systems. The material remains a composite that is poured in place or precast, and used for floor and wall treatments. Aggregates for terrazzo now include marble, quartz, granite, glass, plastic, or other suitable chips incorporated in a binder that is cementitious, chemical, or a combination of both. Following curing, terrazzo is ground and polished smooth or otherwise finished to produce a uniformly textured surface.
Green marble aggregates and white cement give this terrazzo its bright, colorful appearance.
Portland cement-based terrazzo is a highly durable finish well suited to high-traffic floors. It has long been used for commercial applications because it is so durable. It has also found its way into residential properties. Past generations valued terrazzo for its long life, and contemporary specifiers appreciate its durability and further recognize the potential it offers to contribute to the U.S. Green Building Council’s LEED® credits for new construction.
All terrazzo systems are made with zero VOC materials, so terrazzo exhibits little or no offgassing over its life. Terrazzo is composed of about 25 to 30 precent cement or epoxy binders (by volume) with the remainder being natural or recycled aggregates, pigments, and fillers. As this is a decorative finish, aggregates are commonly colored as is the surrounding mortar: white cement with or without color pigments provide the widest range of color choices.
Terrazzo floors are cast with thin forming strips, making it easy to create patterns.
All terrazzo floors have extremely low maintenance costs. Annual stripping and resealing are done with environmentally friendly water-based products. Routine maintenance includes dry and damp mopping, with an occasional spray buffing. In comparison, carpet requires energy intensive maintenance—regular vacuuming and periodic steam cleaning. In many older buildings, terrazzo floors can be restored to their original luster at a fraction of the cost of replacing the finish. In addition, terrazzo is non-porous, does not support microbial growth, and prevents moisture accumulation, helping to maintain a mold-free environment with improved indoor air quality. Further information is available from the National Terrazzo and Mosaic Association.
Using stencils and paint, the concrete slab becomes the artist’s canvas. Some designs are very detailed and intricate and require etching tools to create fine lines.
Artists at World of Concrete in Las Vegas demonstrate their abilities of transferring elaborate drawings onto concrete slab surfaces.
Architectural Pervious Concrete
In today’s environmentally conscious climate, the benefits of pervious concrete to sustainability have reinvigorated interest in these free-draining pavements. But, although it’s appealing for its technical benefits, pervious concrete hasn’t necessarily been attractive…until now. Renewed attention to pervious pavements has led some people to experiment with improvement of the surface aesthetics—and spawned a new type of concrete sometimes referred to as “architectural pervious concrete” (APC).
Most pervious concrete has a sort of popcorn look about it: Uniformly sized aggregate, falling within a narrow aggregate gradation, leads to a concrete with open void areas that promote fast drainage of large volumes of water. Some like the organic, rough-textured look of plain pervious concrete. But for those who want a different look, there are several options for enhancing the aesthetics. Treatments include color, stamping, jointing, and grinding. Read more on architectural pervious concrete.