AluminumAlloyBoats.com

I searched the site and it looks safe to coat the outside of my Edwing's 1/4" AL plate hull bottom with zinc chromate primer???

Boat is 100% trailered and worked in salt water around big marinas with lots of boats plugged into electricity. I want more protection than just a hull zinc and will prime bottom ASAP. Hull is bare aluminum now.

What's a good brand to but?

Mooring, I hope that Chaps, the AAB.com resident coating expert will post in reply to your question?

I think that zinc chromate is mainly considered a 'layering' film and isn't intended for the final out surface? I don't think it will provide much marine growth protection, but since you're trailering the hull I doubt there's much to grow?

It is not a very hard and durable film as I understand so I'd expect it to wear or brush off one the rollers/bunks from trailer loading and unloading? My expectation, not a hard fact.

Last, hull prep seems to be the single biggest factor in paint film success. Where Sanding Blasting is the premium (regardless of blast medium; called 'sand blasting') surface cleaning and prep for all paints- near as I know? Next in order of effectiveness is to establish an anchor patter with something like a 3M Scotchbrite (tm) pad on a belt sander/ roller sander/ rotary sander /buffer. Finally there are some film series that are put on without any anchor pattern or mechanical surface roughening. These last seem to have the higher rework or repair or failure to adhere?

After mechanical abrasion and before zinc chromate would be a conversion from aluminum oxide to chromium oxide done by spraying the hull with an acid to remove the aluminum oxide film- then while still wet from the rinse water and in small areas at a time the chromium oxide forming acid wash, Allodyne, solution is sprayed on and left to dry.

the zinc chromate containing primer is then sprayed onto the chrome oxide film (usually a brown to golden tan- with some greenish hues as visual confirmation of the coverage: NOT BLUE!!) and finally a top coat is applied for wear and growth.

I believe there are product systems where the primer (which may contain zinc chromate) is applied without etching and Allodyne? called self etching primers- but I've not used them so I can't report much about their durability?

Chaps could undoubted give you the best info as he does this work regularly and knows all the products, procedures and results! Might try a PM to him if he doesn't post in reply?

good luck with your project.

Cheers,
Kevin Morin
Kenai, AK

Thanks for the reply, you're correct on many levels. You're a chemist! I'll prep it well for sure. Good point.

All I want is more protection from electricity in the water and zinc primer should work.......I think.

Kevin Morrin is correct, whatever you do, take the effort to sandblast first and you will not be sorry.

Couple of questions . . . Are you experiencing any corrosion or pitting on your hull that has you concerned? If yes, is it a recent problem? Are you using a zinc hull anode? Do you ever plug into shore power? Is the anode on your engine getting used up rapidly?

Hi Chaps,

No real pitting or issues. I have a big zinc on the stern and a 20 pound zinc on a wire I lower when stopped. I never plug in and twin engine anodes are perfect. Boat never sleeps in the water.

I'd switch over to aluminum anodes and call it good. How'd you end up with an Edwing bowpicker way back there? Outdrives?

Aluminum anodes?? The entire boat is aluminum, what would another block of aluminum do?

One long truck ride got it to the East coast.

Twin Honda's now.

Mooring, maybe you could read up a bit on the latest methods of galvanic and stray current protection? BoatZincs is a great service and has some reference articles to help get a handle on the entire topic.

You hull is 5k (and 6k series extrusions) alloys. The newer aluminum "zincs" or anodes aren't in those alloys series; hence they'll give up electrons before your boat. I'm not sure you're reading the galvanic tables exactly? in regard zinc compared to anodes of aluminum?

Cheers,
Kevin Morin
Kenai, AK

I'll give aluminum a try.

Yes I agree with trying the "Aluminum Zincs" sacrificial anodes ! I was chewing through the motor anodes on one of my boats but I switched and now I replace the sacrificial hull anodes every two years and haven't had to replace a motor anode in at least 4 years. I'm on Quonnie Pond and frequent Stonington/watch hill, GLP and mystic which seem to be "hot" harbors.

Cheers


Rick

If you're chewing through zincs that's their job and they're working / saving the hull? Are the aluminum ones working if they're not being eaten up? Now I'm nervous....