Two-coat painting comes out on top

Case Studies
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Reconstruction and rehabilitation of the nation’s bridges is a constant concern because of the time and labor involved. Repainting typically involves the application of a three-coat paint system, and traffic around the jobsite is usually considerable. But the Connecticut Department of Transportation recently found a two-coat paint system that eliminated many of these problems and brought significant cost savings.

Brian Castler, the bureau chief for the Connecticut DOT’s Bureau of Finance and Administration, investigated the two-coat paint system for new and existing steel bridges that have been blast-cleaned to bare metal. The system, manufactured by the Sherwin-Williams Co., uses a polyaspartic coating technology from Bayer MaterialScience . The primer is a VOC-compliant, moisture-curing urethane zinc rich primer that is designed for low temperature application to 20° F, and the topcoat is a fast-dry, single-coat polyaspartic that is formulated for accelerated maintenance painting.

“This is the first two-coat system ever to be placed on NEPCOAT’s Qualified Products List,” said Doni Riddle, vice president for industrial and marine marketing at Sherwin-Williams. “Its performance was judged against
that of conventional three-coat systems.”

“There are four primary advantages of polyaspartic coatings technology,” Riddle said. “It applies exceptionally well in humid environments, it has excellent airless-spray characteristics, it can be applied to a specified thickness of 10 to 14 mil—compared to the 10- to 17-mil dry film thickness of the three-coat
system—and it dries exceptionally fast.”

Castler liked what he heard. So when the time came to paint Bridge No. 1199 over I-84 in Danbury, Conn., he conducted a test. The two spans over the westbound side of I-84 were painted with a traditional three-coat system while the two-coat polyaspartic system was applied to the two eastbound spans. Work on the bridge was conducted during off-peak hours.

Paint contractor A. Lagugeni & Son Inc., based in West Haven, Conn., agreed to participate in the experiment. The contractor closed one highway lane in each direction during work hours. The contractor then blasted the bridge to near-white blast cleaning based on SSPC-SP 10. After blasting, the spans were inspected by both the contractor and the state’s quality assurance inspector to ensure proper surface preparation.

The difference was significant. “The [topcoat] went on like butter,” said Greg Lagugeni from A. Lagugeni & Son. “It was very user-friendly. The paint went on free of sags and runs and covered very well. I wouldn’t hesitate to use it again.”

Because they were attempting to determine the advantages and disadvantages of each method, ConnDOT logged and audited every aspect of the project. According to the results, the two-coat technology was approximately 30% faster than the traditional system. This meant the road was closed for a shorter period of time, and there was less danger for travelers and the work crew.

Additionally, the two-coat polyaspartic system resulted in overall cost savings of about 22% for ConnDOT.

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