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May 25, 2001

Getting creative

  • Modern technology allows concrete to be stenciled, sculpted, engraved, stained and colored.
  • By GARTH E. GLASCO
    Skilling Ward Magnusson Barkshire

    Great Hall section of Everett Station
    Photo courtesy of ZGF
    The Great Hall section of Everett Station, now under construction, features five 40-by-36-foot precast sculpted concrete arches with supporting columns and beams.

    When you think of concrete, what comes to mind? The massive, gray stuff that holds up buildings, durable, but mostly plain and blockish in form? This is perhaps the most typical concrete, easily constructed, strong and cost effective.

    However, advances in concrete mix design and construction technology, along with an increased availability of skilled concrete craftspeople, have produced an ever-widening spectrum of creative concrete applications. Starting with color, the concrete “artist’s” toolkit now includes stenciled sandblasting, form liners, photoengraving, sculpting and more. Concrete can be used to successfully produce the appearance of slate, brick, tile, marble, wood — or even a work of art.

    Colorized concrete

    A common concrete enhancement is colorization, using one of three typical approaches:

    The addition of pigments to the concrete mix before placement (creating integral color) is the easiest and most common method of colorizing concrete. A wide range of color intensity and contrast can be produced by modifying pigment dosage. Concrete ready-mix suppliers are now installing liquid-dispersed color equipment to meter the colors directly into truck mixers. With this system, any color can be formulated from three or four tanks holding primary colors, with the advantage of color consistency. The cost of integral colors for typical slab-on-grade ranges from $20 to $40 per cubic yard.

    Color can also be added to freshly placed concrete slabs by spreading dust-on or dry-shake color hardeners onto the surface, followed by finishing. Color hardeners produce intense, bright colors and can be mixed to produce a wide range of abrasion-resistant finish effects.

    Chemical stains can be applied to new, old, plain or colored concrete surfaces. Acid-based stains react chemically with the concrete and produce an infinite number of results, limited only by the creativity of the installer. Variability, not uniformity, of appearance is the most attractive feature of stained concrete. The price ranges from as little as $2 per square foot for simple applications to $15 per square foot for applications with sawed patterns and multiple colors.

    Stamped concrete

    Stamped concrete is the process of imprinting and texturing the plastic concrete right after placement. Interior floors, exterior driveways, patios and sidewalks can be transformed using stamped concrete surfaces. Many tools and patterns are available to create patterns that simulate brick, tile, cobblestone or other materials. Grooves left by the tools, up to an inch deep, can be grouted with a contrasting color. In addition, texturing skins (thin, flexible pieces of polyurethane) can impart textural options to the plastic concrete in a free-flowing pattern.

    Stenciled concrete

    Stenciled concrete slabs use paper stencils to produce decorative concrete options, providing attractive, economical color and texture combinations. Disposable paper stencils come in sheets that are laid on the plastic concrete surface to produce the look of grouted joints resembling inlaid brick or stone. The stencil is then embedded with more float passes. A dry-shake color hardener is spread uniformly over the surface after excess moisture has evaporated. When the concrete has set enough to bear foot traffic, the paper stencil is pulled up. Areas covered by the pattern remain uncolored and slightly indented, resembling mortar joints.

    Form liners

    Form liners can achieve a wide range of architectural finishes for vertical concrete surfaces such as walls and columns. Securing form liners to the face side of concrete forms results in the replication of rock, brick, masonry block, wood grain or original art graphics.

    “Original art” on concrete surfaces is becoming a large market for the form liner industry. Seattle artist Vicky Scurry has even used recycled tire treads in her work with form liners. The exterior surface of the recently completed Bellevue Art Museum (designed by Steven Holl and Sclater Partners Architects) was created by lining the concrete form with rough-sawn 1-by-2-inch cedar boards.

    Form liners can be either single- or multiple-use and range from $3.50 to $15 per square foot. The result is a maintenance-free concrete wall nearly indistinguishable from a natural stone or masonry wall at about half the cost.

    Stenciled sandblasting

    A relatively new finish for the decorative concrete market, with unlimited possibilities for creativity, is stenciled sandblasting. The process involves sandblasting texture into the surface of concrete through stencils to create patterns, borders or original art. To greatly enhance the effect, the images can be sandblasted through stained finishes into colored concrete, through dry-shake colored surfaces and through textured surfaces.

    Contractors can create their own stencils for simple images using plywood, hardboard, plastic or sheet metal. The material used must resist the sandblasting process for at least one application. Specialty manufactures can create stencils that withstand sandblasting application for multiple uses. Complex images with floating elements in the design use stencils manufactured with adhesive added to one side to bond to the concrete surface for the sandblasting application.

    Stenciled sandblasting is used primarily on horizontal surfaces. However, it is possible to sandblast images on walls and columns. The cost of stenciled sandblasting work can range from $9 to $15 per square foot for the stencil, and $15 to $25 per square foot for installation.

    Engraved and photoengraved concrete

    Hardened concrete can be engraved to transform existing, plain concrete pavements into interesting, decorative finishes. Engraving involves the use of diamond cutting tools to produce repetitive patterns or original graphics. Using concrete stains on the engraved work greatly enhances the final appearance.

    Photoengraving on concrete walls is a new technique similar to the silk-screen printing process. This process allows cast-in-place walls to display intricate relief images of animals or original art, less than a .063-inch relief depth.

    The photoengraving process involves digitizing a black-and-white photograph to produce a screen of the size required for the final image. A surface retarder is applied to the screen, and the retarder flows selectively through the holes in the screen onto a panel of rigid polystyrene, which is then fixed to the inside of the form. The unimpregnated areas of the polystyrene transfer the design to the concrete surface, while the retarder prevents setting of the concrete elsewhere. Washing the surface exposes the aggregate in the retarded areas, revealing the photographic image.

    Sculpted concrete

    All concrete is sculpted, in that concrete, when wet, is a plastic material that is shaped in forms and worked into the final state. This shapability makes concrete the ideal medium for artistic interpretation. A precast approach takes that idea one step further, allowing the creation of concrete sculptures in a controlled environment where creative expression can be economically enhanced.

    Precast sculpture is incorporated into the Everett Station project, designed by Zimmer Gunsul Frasca and currently under construction for the city of Everett. The station is a four-story steel structure with a three-story-high and 60-foot-wide Great Hall through the center. The Great Hall is constructed with a series of five dramatic 40-foot-wide by 36-foot-high precast sculpted concrete arches, with supporting columns and beams. The cross-sectional shape of the arch varies throughout its length. A blend of white and gray cement was used, with a light tan sandstone pigment and light sandblasting to expose the white aggregate speckle. Precast concrete was chosen to consistently manufacture the arches in a controlled environment.

    For complex shapes such as this, the formwork requires craftsmanship equal to fine woodworking. In addition, architecturally exposed precast concrete requires the formwork to be constructed watertight, similar to boat construction, so the formed surfaces appear consistent with no protruding fins. The inside face of the form is lined with a fiberglass mesh, adhered to the plywood using an epoxy adhesive, and the mesh is then coated with an epoxy resin, and finally sanded smooth.

    As the demand for creative expression and decorative detailing with concrete increases, the cost is becoming more economical. Concrete provides the freedom to sculpt any shape, replicate any material, and produce any color — an artistic builder’s dream.


    Garth E. Glasco is a professional engineer and senior associate at Skilling Ward Magnusson Barkshire. He leads the firm’s in-house group of concrete specialists.


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