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  1. #1
    Lieutenant Commander
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    Default Aluminum Corrosion (How to keep from getting worse?)

    In a few weeks I will be putting new sheet foam in and putting the new deck down. My stringers and inside hull have some light oxidation/corrosion from the pour in foam that the boat had. I have powerwashed everything with hot soapy water but there is still a lot of thin white powdery oxidation. This was a freshwater boat it's whole life so what i'm talking about is pretty light.

    Without the pour in foam to hold moisture, do I need to worry about this corrosion getting a whole lot worse in the next 20 years? The boat will be a good weather boat and will be kept inside when not in use.

    Bottom line, Do I need to get all that white stuff off and coat it so it doesn't come back? Or if left as is, do I need to worry about it?

    Sorry for the rambling, but I think you know what I'm getting at......
    Dave P.
    1979 22' Starcraft Supersport V5
    w/ 1985 Evinrude 140 & 1979 Evinrude 9.9

    My original thread about my boat:
    http://forums.iboats.com/starcraft-boats/my-22-starcraft-supersport-v5-yes-pics-416445.html
    My restoration thread:
    http://forums.iboats.com/boat-restoration-building-hull-repair/1979-22-starcraft-supersport-v5-restoration-427003.html

    1995 FourWinns Freedom 3.0 I/O.

    1995 14' SeaFarer LW
    Sold....http://forums.iboats.com/starcraft-boats/i-got-another-starcraft-sf-14-lw-543525.html

  2. #2

    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    I don't know the answer to your question, but if it were me I'd simply buy a few cans of self-etching primer and paint the affected areas, then cover it up with the new floor and forget about it.

  3. #3
    Lieutenant Commander
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Quote Originally Posted by JimS123 View Post
    I don't know the answer to your question, but if it were me I'd simply buy a few cans of self-etching primer and paint the affected areas, then cover it up with the new floor and forget about it.
    Right, but do I need to get the white stuff off first?

    I guess I'm wondering, now that it's all dried out, is it still corroding?
    Dave P.
    1979 22' Starcraft Supersport V5
    w/ 1985 Evinrude 140 & 1979 Evinrude 9.9

    My original thread about my boat:
    http://forums.iboats.com/showthread.php?t=416445
    My restoration thread:
    http://forums.iboats.com/showthread.php?t=427003

    1995 FourWinns Freedom 3.0 I/O.

    1995 14' SeaFarer LW
    Sold....http://forums.iboats.com/showthread.php?t=543525

  4. #4
    Petty Officer 2nd Class
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    Sturgeon Bay, Wi
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    I'm no metallurgist, but I would think that the source of the corrosion came from water trapped between the aluminum and foam in a low oxygen environment. Once it is opened up and aired out, the corrosion should stop. I would not sand it or treat it further. The oxides formed on the aluminum protect the aluminum itself.

  5. #5
    Seaman outdoorsman10's Avatar
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Sounds like a ph problem in the water you are using.

  6. #6

    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Quote Originally Posted by djpeters View Post
    Right, but do I need to get the white stuff off first?

    I guess I'm wondering, now that it's all dried out, is it still corroding?
    Corrosion (i.e., oxidation) is a chemical reaction between aluminum and oxygen, and its accelereted in a moist environment.

    I would guess that it will continue to get wet down there because, after all, it is a boat. True, oxidation in itself is a barrier coating if exhibited uniformly all over the surface. But if we're talking about pitting here, that mau be a different story. If pitted, I would guess that it will continue to "corrode" because it will continue to get wet.

    Now, the question arises - is this an appearance issue or a structural one.

    Since acid etching primer etches into the aluminum, I would think it would etch in the aluminum oxide as well. If that is the case it would serve to seal the corrosion and prevent contact with oxygen.

    Rusoleum's "Rust Reformer" is used on ferrous metals and removing the rust is not necessary. Why not call them and ask their technical department if the AEP would work similarly on aluminum?

  7. #7
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Clean off all oxidation with a mild acid, let dry completely, spray with good primer. Home Depot sells Muriatic Acid in a gallon jug, dilute it with water just so when you apply to the aluminum oxide that it foams a bit, use a brush to clean, rinse with fresh water.

  8. #8
    Rear Admiral
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Muriatic acid is a bit too strong for my liking and will continue in an active state unless completely stopped with a soap and water rinse. If it gets into seams it will be hard to stop properly. Aluma Prep 33 is my preference but even that is a bit touchy. I've found that a Green Scotchbrite pad and Dawn diswashing detergent (soapy water) is the best method. It's a little more elbow grease but it's just as effective. It the metal is really scrungie then a prewash with paint thinner will knock off most of the grime and make it eaiser to get the job done without clogging up the greenie.

  9. #9
    Vice Admiral Yacht Dr.'s Avatar
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Might want to try Alumiprep 33 as sschefer preferred..rinse well with water after your application..

    YD.
    Iboats Helper

  10. #10
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    Default Re: Aluminum Corrosion (How to keep from getting worse?)

    Dilute the muratic before you put it on, let it work and brush a few minutes, neutralize with bicarbonate of soda, wash it off, no problem at all. The soda will kill it on contact. 13 years in water treatment and acid cleaning boilers, cooling systems, etc....no problem. Good Luck!

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