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Polyurethane Coatings Help Keep the Writing Off the Wall at the San Antonio River Walk

Bayer MaterialScience AG : 17 April, 2001  (Company News)
A polyurethane anti-graffiti coating is helping San Antonio maintain the beauty of its premier tourist attraction and reduce city maintenance costs at the same time. The city chose the coating system after the concrete underside walls of the north channel of the San Antonio River had been repeatedly defaced with graffiti.
Flowing through the heart of the city, the San Antonio River is bordered by the famous three-mile River Walk, a tourist favorite. Cobblestone walkways lead to restaurants, unique retail shops and nightclubs along the river, which is shaded by towering cypresses, oaks, and willows and bordered by gardens of flowering ornamental plants.

City officials felt strongly that the graffiti problem, if left unchecked, could damage the reputation of the San Antonio community and unfavorably affect the economy and quality of life enjoyed by its residents.

The San Antonio Parks and Recreation Department first attempted to paintover the graffiti, which resulted in an unattractive, blotchy appearance. As a result, city paint crews would then have to repaint the entire structure, incurring an annual cost of over $5,000.

San Antonio wanted a high-performance, yet affordable, coating system that would enable the city to eliminate costly repainting and provide a long-term solution to its graffiti problem. To accomplish these goals, the city utilized PermaCoat coating from Freda, Inc. PermaCoat, a two-component (2K) aliphatic polyurethane system containing Desmodur? polyisocyanates from Bayer Corporation of Pittsburgh, is specifically designed as a hard coating to withstand power washing up to 1200 psi or to withstand 200 rubbings.

The city hired Anti-Corrosion & Waterproofing, Inc., as the coating applicator. Prior to applying the polyurethane coatings, the crew cleaned the surface and applied a waterborne acrylic paint. Next, the clear 2K aliphatic polyurethane was r oller-applied to approximately 1.5-2.0 mils dry film thickness (DFT). Four hours after the first coat was applied, a second coat of clear 2K aliphatic polyurethane was then roller-applied to 1.5-2.0 mils DFT, providing an anti-graffiti coating that is easy to clean and maintain.

Once the polyurethane coating was applied, various tests were conducted on the new graffiti protection system using PermaClean. PermaClean is a soy-based, biodegradable cleaning solution that is specifically made to remove graffiti from the polyurethane-based PermaCoat surface. To remove the graffiti, the paint crew sprays PermaClean to the surface and allows it to sit for four to five minutes, after which time, the graffiti completely emulsifies and is then rinsed off the surface.

The Johnson Street Bridge, a steel bridge, was painted in 1999. Due to the long-lasting performance properties of polyurethane coatings, it will not need to be repainted for 20 years. For San Antonio, the use of polyurethane coatings has saved more than $10,000 per year in paint costs alone. In addition, the City has been able to reduce its paint crew from three to one due to the low-maintenance requirements of 2K polyurethane coatings.

Due to the success of utilizing 2K polyurethane coatings, San Antonio plans to coat all of its bridges with the PermaCoat coating beginning with the St. Mary's Street Bridge, one of the oldest, most historical bridges in the city. Future polyurethane coating applications also include various murals and artwork in its recreational parks, along with the stone walls (flagstone and fieldstone) along the River Walk.
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