Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

December, 2004

Painting Aluminum Boat

Q. Looking at painting an aluminum boat hull that will be around lots of salt air and water. Constructed from 6061 T6 alloy and 7074 T6 aluminum alloy (not sure if the last alloy numbers are correct). Planning on using Alodine to prep the metal and on using a zinc chromate primer to minimize corrosion and covering with a polyuerathane paint. Does using a zinc chromate primer to provide the extra corrosion protection really work and is there other products around that might be more effective? Is there any special prep work that needs to be done to the primer prior to applying a coat of the polyuerathane?

You coating system sounds good to me, but please make sure that the zinc chromate is an epoxy and not an alkyd or acrylic. The military uses MIL-P-23377 which is a strontium chromate epoxy primer and this is preferred on account of environmental pollution, health and safety.

I don't know how you intend to apply the Alodine but that will be the key to the success of your coating system. I suggest that you apply at least two coats of polyurethane.

Ther application of the epoxy zinc or strontium chormate primer is critical to the success of the system, for both corrosion protection and intercoat adhesion YES, don't leave it out.

Please follow all of the vendor's instructions.

Health and Safety

Please be aware that coatings and solvents are chemiclas and therefore you should always pay attention to proper handling procedures and be prepared to wear protective clothing, such as respirators,gloves, coveralls, etc., and always be sure that your work area is well ventilated.

For further information on the health and safety requirements for the coatings and solvents you wish to use we strongly advised you to contact your local coating supplier and obtain a copy of the Material Safety Data Sheet (MSDS). If possible, go the extra step and look for this information on the website of the product vendor.

Acid etching:

You MUST insure that you are properly protected with goggles, acid-resistant gloves and proper clothing so that you don't injure yourself. For similar reasons, please insure that you keep others away from this process.

Best wishes,

Ron Joseph

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