The Nature of Tilt-Up Concrete and the Role of Sandblasted/Exposed Aggregate Finish
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By Douglas Kozel, AIA – KEE Architecture Inc.
Tilt-up has characteristics that differentiate it from other types of construction, and it is these qualities that make it a unique and expressive way to build. We like to explore these characteristics, looking within the tilt-up technique itself, to create unique architecture.
Think about conventional stick-framing construction. A framework of steel or concrete goes up and then walls are hung from the frame. These walls can be made to look like anything, from the masonry of a Richardsonian courthouse to a Cinderella castle. Postmodern design, thankfully now behind us, depended on this technique. Tilt-up can also be made to match a given idiom. But is this an authentic way to build? We don’t think so. There are examples of tilt-up in Mediterranean, colonial and Georgian styles. However, just because we can do this does not mean that we should.
Figure 3 End walls are 20” thick.
Tilt-up offers the promise of something different, something true to its own technique and how a building is put together. It offers an authentic way to build. Tilt-up walls have an abundance of mass: sheer weight and thickness just waiting to be explored in an architectural composition. The walls we typically use are 12 inches thick! Stick-built construction can simulate this characteristic, but it cannot match its authenticity.
At Spectrum Brands, the thickness of the tilt-up wall is expressed by using deep-set windows with concrete returns. The returns were cast integral with the panels. Another way of revealing the three-dimensionality of the panels was by extending the end panel past the enclosing wall.
We also like the monumental, even heroic scale possible with tilt-up, and when carefully composed, tilt-up’s scale can provide a powerful expression of strength and permanence. At the lobby of Fiskars Brands’ headquarters in Middleton, Wisconsin, slots were cast into the wall of the main stairs where structural support would intersect the wall, revealing the inherent strength of the tilt-up wall. We like this one especially because it brings the exterior material inside where it can be more directly experienced while using the stairs.
Figure 5 Finished panel supporting the stairs
The general configuration of panels as a composition of slabs suggests another approach. At Mead & Hunt, the placement of vertical panels on the east and west elevations helps screen the vertical windows from the sun.
Mead & Hunt; Middleton, Wisconsin. Tilt-up panels turned sideways provide shade to vertical windows on the east and west elevations while expressing the strength of the construction type.
This brings us to the finish used on tilt-up panels. Many finishes are available. However, when panels are sandblasted, the aggregate within is revealed, showing an interesting, raw texture. We are given the chance to see the toughness and strength of the materials that make up the panel.
To accomplish this, we carefully control the color of the panel, using white cement in the concrete mix. This provides a clean, clear matrix that allows the aggregate to come through untainted. For aggregate, we have a couple of favorites. First is regular washed river rock, which is a mix of tans, reds and a few black stones. The second is limestone aggregate, which lends a light buff color to the mix. The degree of sandblasting depends on the project, though we generally favor at least enough to expose the aggregate within to a healthy degree.
This is the river rock aggregate.
Figure 9 Fiskars’ sandblasted aggregate wall. This is the limestone aggregate being evaluated here for compatibility with veneer stone used elsewhere on the project.
Also, we have not been shy about replacing the concrete facing panels with other materials. These include metal, wood, and masonry.
1242 Fourier Drive; Madison, Wisconsin. Conventional brick facing masonry laid up over insulated tilt-up structural panels.
RS&K Building; Madison, Wisconsin. Stainless steel tiles over insulated structural tilt-up panels.
Blackhawk Church; Fitchburg Wisconsin. Wood siding over insulated structural tilt-up panels. Installation above, finished building below.
The technical wonder of tilt-up is that it is load-bearing and space-enclosing, and it includes sandwich insulation, exterior finishes, and interior finishes. This is not only economical, but it also offers the prospect of an authentic architectural expression. And it has a special characteristic shared by much good architecture: it does more with less.
We see tilt-up construction situated as a useful, viable way to build, with its own set of expressive possibilities. Our relationship with Newcomb Construction Corporation is founded on the furtherance of this potential. We put forward this summary of our work together as a chronicle of that venture.
Photo Credits:
Robbins Photography Inc.
Figure 1
KEE Architecture Inc.
Figures 2, 4, 8, 9, 10, 13, 14, and 15
C&N Photography
Figures 3, 5, 11, 12, and 16
Korom Photography
Figures 6 and 7
