Sherwin-Williams two-coat paint system (consisting of Corothane I GalvaPac zinc primer and Fast Clad Urethane topcoat) was applied to three overpass bridges on US 64 in Wake County, NC as a part of a routine maintenance painting contract. The plan was to compare the performance and cost benefit of the two-coat paint system to North Carolina Department of Transportation's (NCDOT's) standard three-coat inorganic zinc/waterborne acrylic system, which was applied by the same contractor in the same general area on five overpass bridges.
The effort and progress of the painting crew at work sites was tracked. An analysis of data confirmed the expectation that the Sherwin-Williams two-coat Corothane 1/Fast Clad Urethane system could save time and labor over NCDOT¿s standard three-coat inorganic zinc/waterborne acrylic system. For a 24,000 ft overpass bridge, the entire operation of mobilization, traffic control, blasting, painting and demobilization could be completed in 20 days with 884 man-hours of labor with the two-coat system and in 29 days and 1239 man-hours of labor with the standard three-coat system. Unfortunately, the savings in time and labor were negated by problems¿including paint delamination and appearance of rust spots¿ that require costly repairs. The problems could be attributed to poor workmanship, absence of a stripe coat on corners and edges, and the design attributes of the Corothane 1/Fast Clad Urethane system that is less forgiving of poor workmanship and mistakes. By eliminating an intermediate coat that could otherwise provide a remedial safeguard against poor painting practices, the Sherwin-Williams Corothane 1/Fast Clad Urethane system is deprived of the redundancy safeguard.
In contrast, the standard three-coat system gave a satisfactory outcome. It is more forgiving of poor painting practices, and minor problems were readily fixed.
This report includes data and observations to support recommendations for improving future bridge painting contracts and enhancing quality assurance methods.
