Painting In-Service Water Tanks

July 1, 2009

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A common practice in water tank repair and maintenance used to involve draining the tank´s content before any coating job can be conducted, because the presence of moisture condensation often interfered with the coating that subsequently led to tank coating failure.

But draining water tanks can be a costly exercise because facilities may not often have a secondary storage container sufficient to hold content when the primary tank is down for painting maintenance. Furthermore, the amount of time needed for the paint job offers some risk to the facility, particularly when the water tank serves as fire protection or when it holds crucial drinking water.

And yet painting jobs for these water tanks are also important to keep them in good condition and for protection and repair of corrosion, abrasion and other damages incurred through the years.

MCU Coating for In-Service Painting

Until recently, water tank exterior painting was indeed a problem, but with the technological breakthrough that produced moisture-cured urethane (MCU) coating, painting water tanks in-service has addressed the problem effectively.

MCU tank coating products are quick-drying and easy to apply. They are more flexible and longer-lasting than standard tank coatings because of their tolerance to more varied application conditions, abrasion-resistance, and imperviousness to wind-blown dust, soil specks and other damage-causing impacts.

Such is the effectiveness of MCU tank coating systems in in-service water tank painting jobs that the American Water Works Association (AWWA) formally recognized the benefits of using MCU through the AWWA D102-03 Industry Standard as OCS (Outside Coating System) 2.

How MCU Coatings Work

MCU coatings are suitable for damp surfaces because, like all urethane coatings, it contains foundational isocyanate groups of atoms that are reactive to hydrogen-based compounds. In water tank coating applications, this reactive hydrogen compound is found in water condensation.

In some tank coating systems, the inclusion of a primer or intermediate coat mixture of micaceous iron oxide (MIO) and aluminum pigments increases the chances of a successful application, because MIO-aluminum overlaps to form a shield that bars moisture and corrosive elements to damage the surface.

To remove out-gassing that may occur from large amount of surface moisture during MCU tank coating application, a simple scraping of pinhole-sized surface damages can be done. MCU coatings ideally cure at above 35 degrees Fahrenheit temperature. A slower curing reaction is expected at lowered temperatures although application is still possible to as low as 20 degrees Fahrenheit.

Water Tank In-Service Painting

The single-component MCU coatings eliminate the need for tank draining during application. For refurbishing or repairing water tank exteriors, MCU provides enduring protection and aesthetic reinstatement to tanks.

Applying MCU tank coating require surface preparation to remove chalking, rust and any loose coatings. An MCU primer is then applied following manufacturer’s thickness specifications. A MIO-aluminum coat is then applied on rusted or damaged areas, topped off with another MCU coating for color restoration.

MCU coatings are used by contractors because their single-component system provides ease of application, allowing contractors to complete the job faster with tolerable maintenance down-time.

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