Precast Solutions - March/April 2008 - (Page 5)

surpassed the capabilities of old-fashioned sacking. Pinholes as small as 1/32-inch, which were ignored on a warehouse wall, have become unacceptable for a corporate office. Sacked areas had streaks that showed through paint, especially on radiused walls where light reflecting on the curved surface revealed every imperfection. Owners were demanding a smooth appearance comparable with drywall finishing. Sackers tried conventional drywall mud, but it is not formulated for exterior applications, and would swell and pop off when it got damp. Portland cement alone would not adhere to the concrete reliably. About six years ago, a California cement manufacturing company began developing a material to address this problem. Matt Sambol, WunderFixx product manager at CTS Cement Manufacturing, Cypress, Calif., recalls, “We got in touch with a very experienced sacking contractor and asked him to try out the material.” The contractor, Ron Drennan, general manager of Restoration Concrete, Long Beach, Calif., felt that this development approach made a big difference. “They came out to the job site to work with the product under real field conditions instead of just developing it in the laboratory environment,” says Drennan. “Nobody else had ever done that. We worked with CTS for five or six months getting it right.” They perfected a finely textured material that was durable, had proper adhesion and would function even under difficult outdoor applications. This effort resulted in the development of a new breed of a dry, premixed patching and repair compound based on premium grade hydraulic cement, fine calcium carbonate aggregate and high-performance polymers. Its color matches a light, natural concrete tonality; some contractors add small amounts of pigment to get a close match to the specific concrete on the job. The new material cures rapidly. It also has very low pH, so it does not cause unwanted chemical reactions with paint, even shortly after application. This combination of properties allows concrete to be patched and painted on the same day. The new compound’s properties include achieving more than 1,500 psi compressive strength. It can be applied in thicknesses ranging from feather-edge up to one-half inch deep. It is sandable but also hard enough to hold a range of textures. It can be roughed up, or it can be sanded with 80- to 100-grit paper for extremely fine finishing. ARCHITECTURAL CONCRETE The new material has been used on one of the largest construction projects in California. The Stater Bros. distribution center in San Bernardino is comprised of multiple concrete buildings surrounded by a 1.25-mile concrete screen wall. The largest building is a 1.45million-square-foot warehouse that will supply Stater Bros.’ supermarket chain. The most architecturally complex structure is the company’s corporate office. The entire project is being sacked by Restoration Concrete, which has adopted the new patching compound as its sole sacking material. Drennan estimates it increases productivity by about 25 percent over the old methods. Drennan points out that his work with the patching compound has set the finishing standard for the Stater Bros. project. Pointing to a row of precast columns flanking the entrance to the corporate office, he recounts that the owner insisted the precast match the smoothness and consistency of the sacking. Using a durable patching compound, complex cast surfaces can be finished to a consistent texture, edges kept straight and sharp. These concrete beams have been skimcoated and left unpainted. MARCH/APRIL 2008 | PRECAST SOLUTIONS 5

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Precast Solutions - March/April 2008 Contents Smooth Move Riding the Waves Comparing RCP With Plastic Pipe Cost-Value Analysis of Storm Sewer Pipe Concrete Testing On a Grand Scale Building Confidence

Precast Solutions - March/April 2008

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