A relatively new option for precast in North America is graphically imaged concrete. The graphic finish can range from a photograph to any type of pattern or design to render a stunning, iconic look. The graphic finish can be repeating
A surface retarder on a printed membrane is placed at the bottom of the form. Concrete is cast atop the membrane containing the reversed image. After the concrete is cured and extracted from the form, the retarder is rapidly washed away with a high-pressure washer, revealing an image resulting from the contrast between the fair faced (smooth) and the exposed aggregate surface. The amount of definition in the design can be controlled by the strength of the retarder and the color variation between the cement and aggregate. Though it cannot be reused, the membrane itself is recyclable. This finish is just as low maintenance—and permanent—as any of the other precast concrete finishes.
A standout example of the possibilities can be found in Denmark. RUM Arkitektur originally won a contract to design a new copper-clad Rødkilde Gymnasium (see page 50). The nearby courtyard would be a social gathering place and learning hub. Copper cladding proved too expensive, so the firm looked to graphic finishes on exposed concrete, aiming to tie in with the school’s older concrete buildings. For a distinctive element and to bring in the “new,” the students and staff were encouraged to write words, statements, and formulas. These were then incorporated into the graphic finish, making the building truly the school’s own.
For this type of finish, it is advisable to discuss the project with a precaster to ensure the specification meets the aesthetic expectations of the architect. Small adjustments to the aggregate or retarder strength can result in superior imaging. Test panels are commonly produced to ensure the mix design and graphically imaged membrane work together to produce the desired aesthetic.
Evaluate, consult, specify
While precast concrete can carry the misperception of being hulking or bland, the availability of a variety of finishes belies this bias. From variations in the mix design and treatments to embedded elements and graphically imaged concrete, precast may be one of the most versatile palettes for architectural expression.
Specifications often include class certification from organizations like Precast Concrete Institute (PCI) and Canadian Prestressed Concrete Institute (CPCI) to ensure adherence to best practices and modern manufacturing processes for architectural precast. Specifying travel distance between the precast facility and jobsite (usually less than 805 km [500 mi]) is also typical, especially if adhering to green building practices. Specific aesthetic treatments should be reviewed with one or more precasters to make sure there is enough detail to allow the contractors to estimate costs and production timetables accurately.
Overall, precast concrete can deliver a multitude of unique finishes complemented by all of precast concrete’s advantages of low maintenance, production efficiency, and resilience. Specifying the proper finish requires an understanding of the architect’s vision and coordination with certified regional precasters to ensure the outcome.
Tony Smith is vice-president of preconstruction and marketing for Metromont Corporation, a precast/prestress concrete manufacturer. He has been with Metromont for more than 27 years with experience in drafting, estimating, sales, business development, and marketing. Smith can be reached via e-mail at email@example.com.
John Carson is executive director of AltusGroup, a partnership of 19 North American precast companies dedicated to precast innovation powered by collaboration. A graduate of North Carolina State University, he has more than 35 years of technical business development and strategic marketing experience. Carson can be reached at firstname.lastname@example.org.