Precast concrete comes in almost an unlimited array of colors, forms and textures including exposed concrete, veneers of traditional materials, or a combination of both.
This section provides basic information on finishing options. More detailed information can be found in the Architectural Precast Concrete Manual (3rd edition).
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Using inset thin-brick techniques on precast’s panelized systems can create the masonry appearance that building owners seek while adding benefits masonry can’t provide. Precast’s inset brick eliminates the long scheduling needed for laid-up brick while removing several trades from the site. It ensures a high-quality, even-spaced appearance that is difficult to achieve with actual brickwork—while eliminating on-site inspections. Using inset brick with precast panels makes efficient use of materials, minimizes time and construction materials, avoids problems with weep holes from falling mortar and eliminates concerns over inconsistent labor expertise, weak mortar joints, efflorescence and disruptions due to bad weather.
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With its ability to replicate such a wide range of materials, precast concrete panels ensure new buildings blend with existing ones. This is particularly true if the original buildings also were made of precast concrete, as previous mixes often can be reproduced.
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Corporate or school names, emblems and other custom touches can be embedded into panels, creating unique accents at an attractive cost. Glass Fiber-Reinforced Concrete (GFRC) can create sculptural forms for custom designs that create a standout facility.
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Special mixes and finish techniques are used on panels to mimic limestone, sandstone, granite and any other type of stone desired. The finishes are produced far more economically than real stone can be laid, and they can be erected much quicker. Form liners can replicate unusual pieces such as cut stone or slate, limiting options only to the designer’s imagination.
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Precast concrete panels offer a plasticity in shapes, curves and geometries that can create any desired look. They interface smoothly with glass and other modern materials.
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Precasters’ capability to tint concrete and provide several tones by using various surface treatments within one panel allow designers to specify any color they want. A wide range of finish combinations and textures can be achieved easily.
The following are the most commonly used finishing techniques when the precast concrete will remain exposed as part of the aesthetic finish.
Smooth or off-the-form finishes show the natural look of the concrete without trying to simulate any other building product.
Sand or abrasive blasting provides all three degrees of exposure noted above.
Hammered-rib or fractured-fin designs creates a bold, deeply textured surface by casting ribs onto the surface of the panels and then randomly breaking the ribs to expose the aggregate.
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Painting is used purely for decorative purposes. The decision to paint should be made early to ensure the finished concrete surface is not so smooth that pain won’t adhere to it easily.
Exposed-aggregate finishes, via chemical retarders or water washing, are achieved with a non-abrasive process that effectively brings out the full color, texture and beauty of the coarse aggregate.
Acid etching dissolves the surface cement paste to reveal the sand, with only a small percentage of coarse aggregate being visible, providing a light exposure.
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Sand embedment creates a massive appearance using 1- to 8-inch-diameter stones or flagstones. The stones typically are placed in a sand bed at the bottom of the mold, and finishing reveals the stone face, resulting in the appearance of a mortar joint.
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Combination Finishes, or two or more finishes, can be readily achieved using the same concrete mix. This procedure will raise the cost of the product, but it will be less expensive than producing a separate unit that must be attached to the primary panel, as with an accent sill.
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Form liners create unique patterns or textures. The liners can be made of wood, steel, plaster, elastomeric, plastic or foam plastic.
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Tooling, usually called bushhammering, mechanically spalls or chips the concrete using any of a number of hand or power tools, exposing the aggregate textures.
Honing or polished finishes are achieved by grinding the surface to produce smooth, exposed-aggregate appearances.
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Staining allows for some of all of the natural texture of concrete to shine through the color, giving finished pieces a more realistic tone. Staining can also be used to create artistic and faux finishes which can replicate alternative building materials onto form liners and precast concrete.
The color of concrete is made up of the paste (cement and water), matrix (paste and sand), and stone (coarse aggregate). Which components contribute mostly, or dominate the color contribution, depends on the finish selected and degree of exposure (The term “exposure” refers to the matrix and coarse aggregate). Form finishes to light exposures receive most of their color from the paste and matrix; whereas with deeper exposures, the coarse aggregate becomes the primary contributor to color.
Paste can be colored by pigments, which come in a variety of colors. However, paste is the binder in concrete resulting from the mixing of cement and water. This is a chemical reaction, and as such, can produce different results when variables are changed slightly. For example, if more water is added to a concrete mix, typically a lighter color of paste will result. This is one reason it is important to specify PCI Certification to help ensure that producers have all the appropriate equipment and quality control procedures in-place. Paste dominate finishes are usually more susceptible to color variation and changes in color with time.
Aggregates come in an array of colors. Other than natural variation of color throughout a particular quarry, once incorporated into precast concrete, aggregates provide great color stability.
Precast can be veneered or embedded with many traditional materials. These include brick, tile, and terra cotta which are usually embedded or cast into precast; and granite, limestone, and marble which are typically veneered via pins or connectors. This allows for differential movement between these materials which are often large sections. Precast offers a faster, more durable, and sustainable method to build with these materials. For specific information on clay and stone veneer, see these Designer’s Notebooks:
Since precast concrete is cast into forms, a variety of shapes and details can be accomplished in precast concrete. Formliners can also be used, especially when repetitive patterns or unique textures are needed. To learn more about forms and design, see the following Designer’s Notebooks.
Precast concrete can be painted or stained. Once only common to see in indoor applications, concrete coloring and replicative finishes of other building materials onto precast or form lined concrete is becoming more popular utilizing concrete coatings.
Painting is common on many projects, but the natural permeability of concrete can make these applications require maintenance over time. Note that latex paints will seal concrete pores and may trap water within the substrate.
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Precast’s plasticity and variety of finishes make it an outstanding choice no matter what style of architecture is desired.
Ensuring the proper look is achieved can be made easy with precast concrete. Precasters can provide finish samples, range samples and large-scale mockups, ensuring design concepts translate into reality.
Mineral stain and similar concrete stains are common choices for finishing on precast and form lined concrete. Concrete stain permeability ensures stain lasts longer and can fuse chemically with the substrate.
Mineral stain, with professional applicative services, can be made to replicate various building materials, such as wood, weathered copper, stonework, and others. Similar to precast veneering, this practice offers more sustainable construction solutions that still yield aesthetically desirable results.
Photo via Nawkaw
Designers can inspect window interfaces, joint connections and other critical elements to ensure they are visually acceptable and will properly interface between trades. Plant visits to discuss technical and aesthetic concerns provide control without requiring constant site supervision.
As the single source for so many architectural and structural components, and the source for brickwork or other finishes, the precaster works closely with the construction team to ensure satisfaction. Overlapping trades and gaps in responsibilities are eliminated when the precaster provides the entire exterior design.
