News from Sherwin-Williams Protective & Marine Coatings

The tiny resort town of Ocean City, Maryland has 3,500 year-round residents. But, when tourist season arrives, the population can swell to 400,000 summer visitors who flock to the 10-mile stretch of the “best white-sand beaches on the East Coast” or come to fish in the “White Marlin Capital of the World.” While tourism is a boon to Ocean City, the huge influx of tourists puts a lot of stress and strain on the town’s municipal water system. That situation has been exacerbated over the years by steadily deteriorating conditions at one of the town’s three water treatment plants. Despite the city’s diligent efforts, the results of repairs made to stop water seepage cracks from occurring in two potable water reinforced concrete tanks were short lived. That’s when Ocean City officials decided to try Sherwin-Williams EnviroLastic® Polyurea coating as a long-term solution for its concrete cracking problem. Because of its flexibility, polyurea is not affected by temperature extremes and is an excellent coating choice for lining potable concrete water tanks, compared to rigid traditional epoxy coatings, which tend to crack as the substrate expands and contracts. Specifically, the EnviroLastic® AR 520 PW was developed for use in potable water applications and is certified to ANSI-NSF Standard 61. Because the lining system can be applied at temperatures ranging from minus 20º F to 250º F, Ocean City was able to complete the coating project in the off-season months of December and January, instead of the busy summer tourist season. Concrete Cracks Sprout Mold, Fungus Ocean City operates and maintains three separate water treatment plants, which produced 1.9 billion gallons of water in 2002. The Gorman Avenue Water Treatment Plant, composed of two operating facilities, includes a structurally sound North Tank that was completed in 1988 and a South Tank, built in 1972, which has deteriorated significantly during the past 30 years. “The worst cracks occurred at the South Tank’s clarifier and pump basin and measured six to eight feet long by about 1/16-inch wide,” says Dave Johnstone of Whitman, Requardt and Associates, an engineering firm where he serves as resident engineer to the town. “Maintenance crews repaired the cracks regularly by injecting them with epoxy or caulking material, but they kept reappearing.” While the cracks on the interior wall of the clarifier did not interfere with its operation, they did pose another problem that surfaced on the exterior of the clarifier. Because of its location in the middle of a residential area, the Gorman Avenue Plant is highly visible to neighbors who can view the facility any time of day. The upkeep of this facility became more demanding as cosmetic problems rose to the surface of the clarifier tank. Mold and fungus began to appear on the exterior of the water tank because of the water seepage. For appearance’s sake, the substrate had to be periodically cleaned and painted to remove the unsightly growth. Sold on Polyurea Because the polyurea technology was new to both Ocean City officials and to the engineering firm, Sherwin-Williams representatives invited them to attend a regional seminar and polyurea demonstration that the paint manufacturer was hosting for a large group of facility owners and engineering firm representatives. Three coating crew employees from B & H Coatings, a Maryland industrial painting contractor, demonstrated the proper techniques for applying the EnviroLastic Polyurea. B & H Coatings began handling polyurea projects in 1995 and has subsequently distinguished itself as one of the premier contractors in the field. With 35 employees, three of the seven B & H crews are certified to apply polyurea with three different manufacturers. The hands-on demonstration gave city officials an opportunity to learn more about the product, its recommended uses and performance in the field. Johnstone observed that reinforced concrete is “notorious for movement.” During extreme temperature changes, it can expand or contract which can cause the concrete to fracture. “After seeing the demo, we were sold on polyurea as a solution to our concrete cracking problem,” he says. “Because of its elastomeric properties – 400% elasticity – the polyurea coating can stretch without ripping and can bridge gaps up to 1/8-inch, making it ideal for protecting concrete substrates.” Off-Season Repairs a Must When B & H Coatings was awarded the South Tank polyurea coating project, city officials requested that the repairs take place during the winter, so there would be no interference with the water treatment’s operation during the peak summer months. B & H Coatings President Bruce Hall says, “Initially, Ocean City asked us to put a polyurea cap on the very top of the clarifier and pump basin which covered just a few feet of the exterior and interior concrete substrate. But after a thorough on-site inspection, we found too many cracks below the cap area, so I recommended coating the entire interior with Sherwin-Williams EnviroLastic® AR 520 PW.” Before the polyurea could be applied, the concrete substrate of the tanks was brush blasted to take off loose concrete and surface contaminants. “Next, our crew pressure washed the debris from the substrate with a Graco 3,500-psi jet,” says Hall. To remove soluble salts and other contaminants from the concrete, the crew washed the entire area with Chlor*rid. “This is standard operating procedure on any B & H project,” says Hall, who uses the cleaner to eliminate residual salt contamination that could affect the adhesion of the coatings. Sherwin-Williams General Polymers Cor-Bond 100 and silica flour were combined to create an epoxy patching compound that was used to fill bugholes and any other imperfections in the substrate. Cor-Bond 100 is a 100% solids, zero VOC moisture tolerant epoxy primer and is specifically formulated for concrete substrates, which require superior toughness and stress relieving properties. The combination of high tensile strength and tensile elongation provide for greater durability under impact and thermally induced stresses. According to Hall, the crew primed the interiors of the clarifier and pump basin with Cor-Bond 100 at 4.0 to 7.0 mils wet film thickness (WFT) during the afternoon when daytime temperatures were warmer and then allowed the primer to dry overnight. “The next morning, we were able to able to apply the polyurea coating at colder temperatures, as the lining system retains its physical properties down to minus 20º F,” explains Hall. Polyurea Stands Up to Cold Weather EnviroLastic AR 520 PW was applied at about 50 mils dft on the South Tank clarifier and pump basin. It dried to the touch in about three minutes and cured in 24 hours. From the contractor’s perspective, the ability to coat the water tanks at freezing temperatures together with the fast cure time resulted in speeding the job to completion. “We would not have been able to do this project at this time of year using traditional epoxy coatings,” says Hall. After completing the South Tank repairs in December 2002, Ocean City officials commissioned B & H to coat the clarifier and pump basin at the North Tank with EnviroLastic AR520 PW. The newer structures were in better condition and did not require as much surface preparation work. As a result, the polyurea installation was quickly completed within two weeks during January 2003. NSF Approved Coating The 100% solids, spray applied aromatic polyurea lining system is designed for immersion service as a seamless waterproof liner for large diameter pipes and tanks conveying potable water and is certified to ANSI/NSF Standard 61. “The low odor, no VOC EnviroLastic AR520 PW is a great long-term solution for the Ocean City water tanks, providing a lining system with extraordinary toughness and flexibility,” says Sherwin-Williams Corrosion Specification Specialist Ed Purdue. Based on the coating’s superior performance at the Gorman Avenue Water Treatment Plant, Ocean City officials are considering polyurea applications for future municipal projects, including containment situations, lining manholes, and a bus wash facility.