The Future of Water Tank Interiors: The Recoating of the Norma Marshall Reservoir

For a glimpse into the future of interior water tank linings, look no further than the refurbishment of the Norma Marshall Reservoir in southern California.

Looking to extend the life of the nearly 40-year-old, 4.8-million-gallon aboveground welded steel reservoir, Rancho California Water District officials opted for a 100% solids epoxy system to replace existing polyurethane- and epoxy-based linings. Those linings had started to show significant wear after only a dozen years, prompting the district to consider a new option.

The high-solids-based strategy offered the water district a quick turnaround – allowing the tank to be disinfected and placed back in service 24 to 36 hours after completion of repairs – for a total project duration of just four months.

Completed in mid-2021, the project also brought the tank into compliance with new NSF/ANSI/CAN 600 standards for potable water – which took effect this January – nearly a year and a half early.

A Chip Off The Old Coatings 

Last recoated in 2008, the reservoir – 160 feet in diameter, with a 34-foot shell height – in Temecula, California, had an interior coated with 30 to 50 mils of a unique hybrid 100% solids elastomeric polyurethane system for the roof and rafters, with an epoxy on the bottom plate and floor.

Before beginning restoration of the tank’s lining, the project’s applicator – industrial and maintenance services provider Advanced Industrial Services, Inc. (AIS) – found the existing coatings to be in poor condition.

While most tank owners may hope for a coating system to last twice as long, the Norma Marshall’s interior was experiencing significant delamination. Coatings were blistering, peeling and becoming detached from the steel, which compromised the integrity and, potentially, the longevity of the steel tank.

Initial inspection revealed conditions in the tank’s vapor zone were especially compromised, including significant rust on rafters, clips and the center column where the elastomeric polyurethane system was used.

The tank’s interior provided ample space for mobilization, yet removing old coatings from the roof proved initially challenging. Given the thickness of the existing lining, crewmembers forewent abrasive blasting – reasoning that blast media would have trouble penetrating the thick layer. They instead elected to use air-powered chippers to get under the coating and remove it.

Next, using recyclable abrasive steel grit 25, crewmembers dry blasted all interior tank surfaces to the SSPC-SP 10 Near-White Metal Blast Cleaning standard, leaving a steel surface free of coatings and residues with a minimum 2-mil profile to promote adhesion. After collecting the grit, crewmembers placed it in a recycler to separate out paint chips and other debris. Later in the job, upon completion of the roof and shell, the project team used a self-propelled, self-contained shot blaster to reduce dust and particles while preparing the floor.

The tank also required the protection of an intricate system of internal piping that needed additional care during surface preparation and the application of coatings.

Before beginning interior blasting, contractors used small mobile cranes to temporarily remove and safeguard the interior mixing system’s piping – made up of high-density polyethylene (HDPE) piping, steel appurtenances, fittings and supports, and Tideflex® check valves – which can be especially susceptible to corrosion. 

Charting New Waters

The majority of ground storage reservoir tanks feature multi-coat systems to cover their interior roofs and rafters, which are full of sharp angles and edges where angle iron is welded and bolted to the structure to give it strength. The multiple coats are meant to ensure adequate coverage of all edges, outside corners, bolts, crevices, and other irregular steel surfaces. However, the Norma Marshall tank’s owner recognized the benefits of using an edge-retentive 100% solids epoxy, which can be applied in a single high-build coat, to extend the tank’s service life.

The material would need to provide corrosion resistance for all vital areas of the tank, as well as excellent edge retention, which included the ability to sufficiently cover corners, angles and bolts with a single coat.

These preferences contributed to the choice of Sherplate™ PW, a two-component, edge-retentive, low volatile organic compound (VOC) rating, low odor, ultra-high-solids epoxy amine coating from Sherwin-William Protective & Marine. The product replaced the elastomeric polyurethane that had been previously used on the tank. In addition, it displaced traditional solvent-rich epoxies that would have otherwise been used and would have required additional coats and longer cure times.

The Sherplate PW coating system was also designed to control corrosion in the vapor space above the water line and the structural steel of the roof, including beams, as well as to protect the remainder of the immersed tank.

The coatings system was also compliant with NSF 600 ahead of the new standard’s implementation in January 2023.

“We aimed to be ready for where the industry is going,” said Pablo Gamboa, Project Manager, AIS. “On this project, we were ahead of the game.”

Applicators began by applying a stripe coat of Dura-Plate® UHS Primer to critical areas such as weld seams, edges, angles, bolts and more (Figure 1). This two-component epoxy amine, with its ultra-high-solids formulation, provided exceptional surface wetting and adhesion properties. The primer, recommended for immersion service in various tanks, was applied with ease at a thickness of 4 to 8 mils DFT using a combination of brushing and rolling techniques.

Subsequently, the interior surfaces of the reservoir, including the roof, shell and floor, along with edges, nuts, bolts, welds and joints, received a topcoat of Sherplate PW (Figure 2). The crew applied two coats to the roof and rafters, for a total thickness of 24 to 36 DFT, which offered extra protection for good measure. The floor and shell received one coat, at a thickness of 24 to 36 mils DFT, sprayed to ensure optimal coverage (Figure 3).

Sherplate PW, a specially designed coating engineered for immersion service in potable water pipes and storage tanks, proved instrumental in providing superior protection, with its high-build properties and its greater than 70% edge retention.

Applicators used nearly 2,000 gallons of the fast-curing coating, which also has a low VOC rating that met all standards set by the region’s South Coast Air Quality Management District, which are some of the strictest in the country. 

Precison in Tight Spaces 

Throughout multiple visits, Sherwin-Williams Protective & Marine technical representatives provided assistance to the AIS crew, especially during the roof and subsequent floor coating applications. They helped the team set up two plural component pumps on-ratio, which ran concurrently, using transfer pumps to pull the coatings directly from the drums.

This efficient setup enabled applicators to easily reach the tank’s upper corners and crannies using scaffolding. A crew of three, consisting of an applicator, a crewmember adjusting the sprayer and another conducting wet film thickness (WFT) mil checks, successfully completed the challenging roof area in a timely manner.

“Sometimes, getting in tight spaces can make the job difficult,” said Gamboa. “Everything goes a lot smoother when tech support is out there – making sure our equipment and coatings are set. When they give us the thumbs up, we know we can rock and roll.”

Sherwin-Williams technical representatives proved invaluable to the success of the project by providing essential consumables, including spray tips and housings. In addition, they imparted their expertise to water district personnel on the proper repair of any damage to the coatings.

With coating thicknesses notoriously difficult to measure or inspect in the tank’s roof and rafter areas, applicators coated these sections with confidence, guaranteeing the tank’s durability and service for the benefit of the Rancho California Water District and its patrons.

“We always appreciate when the manufacturer provides direct support to the project and makes sure the crewmembers feel comfortable and confident in getting the job done,” said Jake Wiley, Assistant General Manager – Engineering & Operations, Rancho California Water District.

After completing the roof and shell coatings, applicators cleaned, prepared and coated all the mixing system components (Figure 4) outside the tank and then reinstalled them with new non-asbestos rubber gaskets.

During the project, unforeseen mechanical issues emerged with the tank’s support system. Following the observation of metal loss from the blasting, the project team had to undertake extensive repairs, including the replacement of the center vent and seven rafters. The team also took on the task of fixing nearly 60 rafter-to-shell clips by fitting them with new nuts and bolts – and installed an entirely new set of earthquake rods to reinforce mid-span bracing.

With sometimes as little as 60 days to get tanks back in service, the consistency of the Sherplate PW coating system helps AIS complete restorations in a timely manner, even when unexpected issues arise.

“The fast-curing nature of the coatings helps us get on and off projects – there’s no running fans to move air and cure out a tank,” said Gamboa. “Sometimes the tanks can be a tough blast. With these coatings, I know I won’t have delays with coatings on the back end. I can’t afford to wait for paint to dry.”

Back in Service

An owner-led inspection confirmed the thickness of the coatings, passing with flying colors – and found only three holidays.

“For a tank that size, to have only a handful of holidays was impressive,” said Wiley. “The few touchups cured quickly, and the tank was back in service soon – welcome news to everyone.”

The project team received honorable mention recognition in the 2022 Sherwin-Williams Impact Award program, which recognizes projects that demonstrate the use of high-performance coatings from Sherwin-Williams Protective & Marine.

With the high-solids coatings containing no VOCs, the prospect of extractables in the stored water was nil – helping the tank pass water safety tests with ease and ensuring Rancho California Water District customers will have quality drinking water for years to come.

“The project gave us no concerns about what may leach into the water and affect quality,” said Wiley. “Given new national standards, this approach could serve as a model for tanks anywhere in the country.”

ABOUT THE AUTHORS

Paul Trautman has 30 years of experience in the paints and coatings industry working in various capacities, including 20 years with Sherwin-Williams Protective & Marine, where he is currently Market Director of the Water Infrastructure segment. Trautman has authored technical papers related to protective coatings and presented educational programs for the Society of Protective Coatings (SSPC) Coatings+ Conference and regularly hosts educational luncheons for municipalities, industrial facility owners and consulting engineering firms. Contact: Paul.Trautmann@sherwin.com

Josh Skinner is a Senior Technical Sales Representative, with an owner and engineering focus in water and wastewater, for Sherwin-Williams Protective & Marine in the Los Angeles, California, market. With the company since 2008, Skinner has served as Operations Manager, Store Manager and Commercial Sales Representative in the Stores Group of The Sherwin-Williams Company. Contact: Josh.D.Skinner@sherwin.com