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topic 29978

Best way to paint a cast aluminum boat stern drive

adv. northern banner

(2004)

Q. I would like to know of a preferred method of painting or coating my Volvo outdrive lower unit, which is aluminum casting.

If you are not familiar with stern drive power on boats, they are the used to transfer power from the boats engine to the prop and is usually submerged (in my case, in fresh water for 4 months each year). My drive has be power wire brushed to remove any failed paint.

Because I don't have access to a oven, the process would have to include air dry times between processed elements.

I have tried using zinc chromate primers and both lacquer and enamels for sealing and cover coats with little durability, usually lasting less than one season.

Any help you can provide would be greatly welcomed.

Thanks,

Dale

DALE B [last name deleted for privacy by Editor]
boater - PITTSBURGH, Pennsylvania


(2005)

Q. To Dale B,

I have the same problem as you described for your boat (same aluminum outdrive, paint won't adhere). How did you correct it?

Donald H [last name deleted for privacy by Editor]
- Syracuse, New York


(2006)

thumbsdown DON'T TRUST ADVISE FROM YOUR MARINA WHERE YOU ARE DOCKING YOUR BOAT. GET INFORMATION FROM THOSE WHO ARE NOT LOOKING TO PROFIT FROM YOU.

Jack C [last name deleted for privacy by Editor]
- Sayville, New York


April 2008

A. Thanks, Jack. That's exactly what they're trying to do here. Got any? :-)

Ideally, the proper pretreatment of bare aluminum is actually a chromate conversion coating consisting of two steps: cleaning with an aluminum cleaner like Alumiprep 33 and chromate conversion coating with a product like Alodine 1201 [linked by editor to product info on Amazon] before painting. This is not something really safe for consumers, however, so you'd probably be best off trusting it to professionals.

A treatment that is not as good as chromate conversion coating, but better than sanded aluminum, is phosphatization. Commercial Naval Jelly [linked by editor to product info at Amazon], although designed for steel, will give your aluminum a bit of a phosphatization (I haven't tried it myself though). Good luck, and if anybody has tried it, please give us some feedback.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


Latex Self-Etching Primer

August 2, 2008

A. A brush coat of phosphoric acid and then a self-etching primer for aluminum should do the trick. Paint with a good quality marine paint and it should last for years...

Rich Poythress
- Boise, Idaho


April 24, 2009

A. DON'T use a wire brush on aluminum body drives. The metal will become impregnated into the aluminum. Use sandpaper or sandpaper flapper wheels only. Good Luck!

Richie Rich
- Laplata, Maryland

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Ed. note: Readers may also be interested in letter 13648, "Painting a Mercuiser aluminum outdrive"




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