HELP!

Using Underwater Coatings on Metallic Surfaces

In Salt Water - A Warning

Your Host and Tour Guide:

Paul Oman, MS, MBA - Progressive Epoxy Polymers, Inc.

Member: NACE (National Assoc. of Corrosion Engineers), SSPC (Soc. of Protective Coatings)

"Professionals helping Professionals"

Epoxies bond to surfaces at the molecular level by tiny electrical charges. Sometimes in marine settings there can be pre-existing electrical charges in the underwater environment that interfere with the bonding mechanism of the coatings. Such electrical cells can be either intentional or accidental.

Active or passive cathodic protection systems, designed to protect against underwater corrosion, will produce electrical fields that disrupt coating bonding. Dissimilar metals in the immediate vicinity (identified or unidentified) will also produce stray electrical fields. Even chemicals and pollution in the water may be responsible for or enhance the voltage of existing underwater electrical cells. The problem is more often observed in dirty harbors, full of unidentified metal junk, and chemical/industrial waste. Even ongoing arc welding on a ship will produce electrical charges on and around the hull. Ships tied to dockside facilities with their own cathodic protection systems or sloppy electrical systems, can cause underwater coating bonding problems on conductive (metallic) surfaces. Generally there is no problem on non-conductive surfaces such as concrete and wood.

The method to evaluate the application and bond of underwater coatings on conductive metallic surfaces in seawater is not in a bucket of harbor water, but under actual conditions. What bonds and works well at Dock A, may not work at Dock B or when tied up to Facility C due to identified or unidentified electrical charges at that site.

Almost without exception, bonding problems associated with ‘underwater painting' are site specific and related to electrical cells formed in a conductive medium (seawater) on a conductive surface. Always test in the actual marine environment before committing to any underwater coating project as this type of coating failure is not covered by product warranties.

BECAUSE OF THE SITE SPECIFIC, KNOW OR UNKNOWN CAUSES OF UNDERWATER BONDING PROBLEMS, NO WARRANTY CAN BE OFFERED OR PRODUCT RETURNED BASED UPON UNDERWATER BONDING PROBLEMS AT YOUR LOCATION. WE WILL WARRANTY THAT OUR UNDERWATER EPOXIES WILL BOND TO SUITABLY PREPARED WOOD, METAL AND FIBERGLASS SURFACES IN SALT OR FRESH WATER IN A GLASS OR PLASTIC TANK. TO AVOID COSTLY PROBLEMS ALWAYS TEST ANY UNDERWATER EPOXY FOR COMPATIBILITY AND ADHESION PRIOR TO ORDERING PROJECT SIZED VOLUMES.

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