Located on the west bank of the Mississippi River, just east and across the river from uptown New Orleans, Louisiana’s Gretna Wastewater Treatment Plant has faithfully served its 18,500 residents and 900 businesses for 30 years. It has supported the city’s explosive growth and increased demands on municipal services over the last several years. But in May 2012, it was clear that years of use and exposure to harsh treatment chemicals had caused significant deterioration to the treatment plant’s primary and secondary concrete clarifier tanks, requiring complete rehabilitation and re-coating.
Although Gretna’s Department of Water and Sewage (DoWS) agreed on the urgency of the rehabilitation project, selecting an appropriate tank lining system posed a challenge. The goal was to find the most cost-effective solution that would successfully create a solid containment.
After short consideration, the owner chose a system by International Paint and a local contractor out of Baton Rouge, La., to do the job. Not only did International Paint’s solution offer more bang for their buck (lower necessary mils for less money, but also the same positive results). Their solution also offered a one-coat lining system that could provide the robust coverage and long-lasting corrosion protection needed to restore the concrete tanks and extend their maintenance life-cycle.
Although skeptical about the results of the one-coat system, the client was convinced that it was the way to go. (Coatings samples and independent test results on the system helped prove the point of its adhesion, coverage, aesthetic, and durability properties.) Engineers were duly impressed by the evidence and cost-savings associated with reduced labor and materials. But the fact that International Paint’s Ceilcote 663-SG Ceilgard is one of the very few tank lining systems to pass the industry’s respected Redner Test with flying colors was the deciding factor in giving the contractor the green light to move forward on the rehabilitation project.
The Redner Test takes its name from John A. Redner, departmental engineer for the Sewerage Department at the County Sanitation Districts of Los Angeles, Calif. Redner has published results of testing the acid resistance of many sewer lining repair coatings in a simulated sewer set-up, and his test was developed to objectively assess the in situ application issues and the acid resistance of coatings on concrete sewer pipes.
“It was very gratifying to be able to present the DoWS with such compelling evidence to support the performance and cost-efficacies of the Ceilcote 663-SG Ceilgard lining system,” said International Paint’s Dennis Ellard. “Municipalities have to rely on leaner budgets every year, yet cannot compromise the safety and long-term protection of equipment assets. We are confident that this low-volatile organic component (VOC), single-coat tank lining solution provides the protection and sustainability the city needs, at a price that supports good stewardship.”
Seconds First
Karl Lobell, co-owner of and field manager for Professional Application Services, and his four-to-eight-man crew began work on the Gretna Wastewater Treatment Plant in June. The primary and secondary tanks are comprised of a row of four concrete basins 11 feet (3.35 m) high and 117 feet (35.66 m) wide with concrete walls dividing each of the four tanks. More than 12,000 square feet (1,114.8 m²) of concrete would ultimately need repair and re-coating. In order to minimize production downtime, plant officials chose to shut the secondary tanks down first and keep the primary tanks in operation until the rehabilitation was completed.
After all of the water was drained from the secondary tanks, four of Lobell’s crewmen prepared the concrete substrate by de-greasing the walls with a bio-degradable detergent to NACE 6/SSPC-SP-13 Surface Preparation of Concrete. Protected by Tyvek suits, Bullard hoods, face shields, and 3M air purification respirators, the crew then used an RPO 1-72 high-pressure wet-abrasive blast to remove the old degraded concrete and expose the intact concrete and aggregate. This was done in adherence to the International Concrete Repair Institute’s (ICRI) concrete surface profile (CSP) number 5.
Due to the severe deterioration of the concrete, it was necessary to use an underlayment material to fill in bug holes and create a smooth surface prior to application of the primer. Then, Lobell brought in an additional four guys to start applying the coatings.
A Crown Mortar Mixer and Airplaco Spraymaster SM-78-G pump were used to spray-apply Ceilcote 400-MP Corocrete onto the wetted substrate. “It’s hard for four guys to keep up with the nozzle guy,” said Lobell. It’s easy for the guy on the nozzle, but for the guys assigned to “knocking down,” they had to hustle. The four crew members following after the applicator had to use trowels to remove, or knock down, any extra underlayment to reach an average of one-half-to-one-inch (1.27?2.54 cm) thickness.
Some areas were so degraded that it took up to six inches (15.24 cm) of repair material to renovate. About 12 hours after the underlayment was applied and fully cured, the Professional Application Services crew conducted a water-wash at 5,000 psi (34,473.79 kPa) using an oscillating nozzle. This process, which was done to remove any laitance or contaminants from the walls to achieve a 60-80 grit surface profile, was performed on the entire tank to meet the DoWS’s strict regulatory guidelines for repairs to indoor tanks. The next morning, the crew completed a visqueen moisture patch test to ensure that all of the surfaces were dry; after 24 hours, they checked the test and were able to move on to the next step. To promote adhesion to the tank’s substrate, the crew used a Graco 60:1 pump to spray-apply Ceilcote’s 680-M primer at 5.0 mils (127.0 microns) to seal out-gassing of the concrete. It took the crew 12 hours to apply this layer and overnight for it to cure.
Over eight hours, the crew spray-applied a single coat of the 100 percent solids Ceilcote 663-SG Ceilgard lining over 4,000-to-5,000 feet (1,219.2?1,524.0 m) at a time. They used a Graco 68:1 airless spray pump to apply the coating to the prepared surfaces at 23 to 25 mils (584.2?635.0 microns).
Add It Up
It took the Professional Application Services crew six months (off and on) over two phases to complete the job. Lobell and his crew have a long history working with this coating product. “I’ve worked with dozens of tank lining systems over the years and my team continues to be impressed with Ceilcote’s remarkable ease-of-application and durability,” said Lobell. “With the turn-key Ceilcote system of repair mortar, primer-filler, and lining, the Gretna Wastewater Treatment Plant will receive outstanding protection of its equipment long-term, while having saved significant costs in labor and materials at the same time.”
While protective coatings contracts typically represent a very small portion of a municipality’s overall capital improvement budget, their role in helping protect equipment assets against damage and corrosion long-term is critical. It’s important, therefore, to spec the right solution and to apply the coatings properly. That balance can make the difference between extending the life-cycle of the project to 30 years or more and having a severe coating failure. After all, it’s not just about the coating or the contractor. The whole is greater than the sum of all parts. And on this job, that meant that the Gretna Wastewater Treatment Facility received one superb solution.