Creative Forming and Finishing of Tilt-Up Concrete
By: Ed Sauter
Tilt-Up Concrete Association
For years, if you were to ask almost anyone in the construction industry, they would have told you that
the terms “aesthetics” and “Tilt-Up construction” were mutually exclusive.
Developed at the beginning of the 20th century, Tilt-Up (the construction method by which concrete panels are cast on site and then quickly “tilted” into place) developed a reputation as the perfect means to construct big-box warehouses—and little else.
However, with the rapid growth of Tilt-Up has come an infusion of technology and creativity that is breaking the stereotypes of what the construction method can and can’t do.
As a result, more and more contractors and owners are embracing Tilt-Up construction, not only for its speed and cost- effectiveness, but also for the limitless creative possibilities it provides.
ARCHITECTURAL TILT-UP: HISTORY AND GROWTH
In 1909, Thomas Edison described Tilt-Up construction as “a construction method which eliminates the cumbersome practice of constructing two wooden walls to get one concrete one.” But even then, Tilt-Up was already much more than this simple definition suggests. Although it eventually came to be characterized with bland, industrial buildings, in its infancy, Tilt-Up showcased plenty of architectural features. The United Methodist church in Zion, Ill., located in a Chicago suburb, is one of the earliest examples of Tilt-Up construction featuring intricate detailing on its façade and it is still in use today. Unlike some of today’s integral architectural treatments, though, these were merely decorative precast or terra cotta elements that were cast into the face of the panel before it was tilted into place.
The rapid, inexpensive process of Tilt-Up construction that we are familiar with today came into its own just after World War II, with the introduction of two material handling innovations. The ready mixed concrete truck allowed quality concrete to be transported in large quantities to the job site, thereby eliminating the considerable expense of having an on-site batch plant. And the mobile crane provided an economical means for lifting the large, heavy panels into place.
In the past decade, Tilt-Up construction has experienced unprecedented growth. In 1995, Tilt-Up accounted for 129 million square feet of panels, representing a quarter of a billion square feet of building space. By 2000, Tilt-Up had grown to 270 million square feet of panels and three quarters of a billion square feet of building space—and the numbers continue to grow. But it’s not just the square footage that’s increasing. Each year, Tilt-Up expands its reach beyond big-box construction into smaller buildings such as schools, retail centers, offices and churches.
TILT-UP MYTHS AND REALITIES
The primary reason for the growth of Tilt-Up among smaller structures is the growing realization that the method offers owners and developers an almost unending range of creative possibilities. In fact, as many are learning, Tilt-Up can even undertake certain feats that would either be impossible or considerably more expensive with other construction methods. In the process, many of the myths that have plagued Tilt-Up construction for years are being proven wrong.
For example, it was long thought that Tilt-Up structures could only incorporate a few small windows—a highly undesirable proposition for buildings such as schools and offices, which would be fully occupied during the day. However, the average Tilt-Up project today incorporates numerous windows in various shapes and sizes—and, better yet, configuring openings for these windows, in particular for unusual shaped openings, is often easier in Tilt-Up than in other construction methods.
Another long-held misconception about Tilt-Up construction is that it must be confined to simple, rectangular shapes, therefore giving any building constructed with the method a warehouse-type aesthetic. Although it’s true that rectangular panels are the most economical option, virtually any shape of panel can be used in Tilt-Up construction today. Computer software and other improvements in the lifting industry automatically calculate centers of gravity and other parameters necessary to erect and brace complicated panels.
Tilt-Up construction’s former focus on large industrial buildings was due in part to the fact that their ample floor surface area provided the space necessary to cast wall panels. While an 80- to 85-percent wall-to-floor ratio is still desirable for panels that are cast on the slab, this measurement no longer restricts the size of the structure that can be built. A host of other casting techniques, including casting beds and stack casting, make Tilt-Up a viable option for buildings that don’t meet this guideline. In addition, the old notion that walls needed to be at least 20 feet high to be a candidate for Tilt-Up has also fallen by the wayside. The design and finish of the building, construction schedule, equipment availability and experience of the design team can all help determine whether wall heights shorter than 20 feet are cost competitive.
Much of the growth in Tilt-Up construction has occurred in the Southern half of the United States—however, contractors are now realizing that Tilt-Up can also be an effective construction method in colder climates. The only requirement is a one- to three- day window in which the concrete can be cast—after that, reasonable precautions can be taken to prevent the panels from freezing until they’re ready to lift. Additional technologies, such as ground-heating systems or specially formulated concrete mixes, also can be used to extend the available building time in Northern states.
TILT-UP POSSIBILITIES: FORMING
There are a couple of broad trends that are helping shape the face of the Tilt-Up industry today by pushing the boundaries of the method’s architectural possibilities. One that is just beginning to be explored involves using the unique nature of Tilt-Up construction to create interesting panel forms that can be used in a variety of ways. Because concrete is such a fluid material, it can easily be cast into any shape that can be formed. In addition, Tilt-Up’s use of a horizontal casting surface makes shaping these unique forms quite simple.
Simple curved panels are one of the most common elements used on Tilt-Up buildings. While not a wildly unusual shape, curved panels can still have a major impact when used creatively. Curved panels can be concave or convex, depending on the desired aesthetic. They need not be full height, either—often, convex spandrel panels will be set atop Tilt-Up columns to create a dramatic entranceway. If a structure is designed to incorporate a large circular wall, the wall typically can be constructed using several radius panels. Radius panels in a variety of sizes also can be used to provide softer, rounded corners for traditional rectangular buildings. Other techniques such as shadow paneling (placing one panel in front of another) can be employed solely for artistic effect.
Because attaching unusually shaped panels can be tricky, many designers and contractors will break the
linear plane only at the top of the wall to get around the restrictions that come with attaching panels to the foundation or to adjoining panels. In some instances, even panel sides can “escape” beyond the edges of the structure to add a new dynamic to the building. Another way to incorporate unique forms into a traditional rectangular structure is through the use of interlocking panels. These panels are cast in a variety of shapes (usually using different finishes to give them textural interest), then fitted together like puzzle pieces. This type of aesthetic would be virtually impossible to achieve with any other construction method, but with Tilt- Up, it isn’t any more difficult than forming a conventional rectangular wall.
Beyond shape, another way to add interest to panels through forming techniques is with the use of openings. Windows and doors are the most obvious panel openings, but purely aesthetic openings, referred to as “voids,” also can bring plenty of drama to otherwise plain panels. Used on panels that extend beyond the boundaries of the structure, voids let light and sky through to create a unique, three- dimensional look for the panels.
Although windows and doors are not structural elements, they can still add plenty of beauty when used creatively. One common Tilt-Up practice is to incorporate “ribbon windows”—long, thin strips of glass that stretch completely across the façade of a building. In reality, portions of these “windows” aren’t windows at all; rather, the glass is placed in recesses that are cast into the panel, giving the illusion of windows. However, these false windows may often have real windows incorporated inside—just not in the continuous form that’s visible from the outside of the building. Illusions aside, it’s quite possible to design a Tilt-Up building that incorporates a number of large window openings, as long as the panels are designed with sufficient legs to provide strength during lifting. These large windows can even take on a variety of shapes, such as a Gothic arch for a church building.
Architectural interest doesn’t just have to be generated during the casting process, though. The way the panels are placed together can go a long way in creating an eye- catching structure. Shadow panels, overlapping panels and freestanding panels that extend beyond the four walls of the structure are an easy way to make a statement.
TILT-UP POSSIBILITIES: FINISHING
The other broad trend defining architectural Tilt-Up today is the desire to replicate traditional building materials such as brick and stone. While the real materials can be costly and time-consuming to install, their Tilt-Up counterparts, by contrast, are fairly easy and inexpensive to incorporate. A variety of finishing techniques can impart these classic looks on a building’s surface.
Reveals— narrow, decorative indentations (usually 3⁄4-inch deep) in the face of the panel—are formed by applying strips to the slab (casting surface) before placement of the concrete. Something as small as a change in reveal depth – for example, from 0.75-inch to 1.5 inches – can dramatically alter the look of the structure. The reveal forming strips have sloping sides for easy removal. However, keep in mind that the depth of the reveal must be considered in the structural analysis of the panel.
Form liners are another easy way to bring interesting detail to an otherwise plain panel. These liners— typically made of a thin plastic that is either vacu-formed or stamped—are available in a variety of textures that replicate several different materials, including wood, corrugated steel and bush-hammered concrete. Even customized images (such as logos) can be fabricated from foam and placed in forming beds to create a truly unique building façade. Not only do form liners provide a way to introduce the illusion of other materials to an all-concrete structure, but they may also help hide inconsistencies in the panels’ finishing. A word of warning, though: form-liner patterns can be hard to implement on large panels, so it may be best to divide the panel into smaller areas to better control the pattern.
While details cast into panels may work in some situations, others may warrant what is referred to as applied ornamentation—decorative elements, made from materials such as precast concrete or stone, that are added to panels once they have been formed. One of the most popular forms of applied ornamentation are Exterior Insulated Finishing Systems (EIFS). The popularity of EIFS lies in part in their ability to replicate historic styles such as Art Deco and Gothic Revival.
Another way to achieve a classic, traditional style is by using cast-in elements. These elements are real masonry materials, such as thin brick, stone or tile, which are cast into the face of the concrete panel. Unlike full masonry, however, using these materials in conjunction with Tilt-Up is both quick and cost-effective. The use of cast-in elements has allowed Tilt-Up to gain ground in markets previously dominated by masonry construction.
While cast-in elements certainly provide the most realistic option for creating a traditional finish, a more popular, economical approach is to apply one of a variety of finishing methods to the face of the concrete once it has set. These methods include exposed aggregate, polymer- modified cement, coatings, paint, and stamped or rolled finishes, and they often are used in conjunction with other techniques discussed above to impart maximum impact on the look and feel of a structure.
Exposed aggregate is often used to impart a rougher, more natural feel to a building.
A similar natural effect can be achieved through the use of textured coatings. These coatings, some of which resemble fine-grained granite when dry, are typically thicker than paint, and can be used to add color as well as texture to the surface of the building. While they’re typically more expensive than traditional paint, they usually last longer and can provide a significant upgrade to a building’s aesthetics. Polymer- modified coatings are similar in application; however, they have the ability to replicate even a wider variety of different building materials. Polymer-modified coatings also have the added bonus of being virtually maintenance-free.
Finally, Tilt-Up buildings can be a wonderful blank canvas for trompe l’oeil painting. French for “a trick
of the eye,” trompe l’oeil painting creates a detailed faux exterior for the building, right down to the shadow created by a piece of molding. A Tilt-Up building for a fire equipment company in Phoenix took advantage of this method, creating an entirely fake Romanesque-style edifice, complete with intaglio bas relief panels, landscaping stones and rustication.
As the breadth of decorative techniques described here demonstrates, while Tilt-Up may have gained a reputation for creating bland, industrial buildings in the past, this is far from the case when it comes to today’s Tilt-Up projects. As the construction method continues to grow, the same combination of technology and creativity that has made these feats possible will undoubtedly create an atmosphere in which the only limitation on a Tilt-Up project is the imaginations of those designing it.
