preparation of interior rust on steel hull

Discussion in 'Metal Boat Building' started by owensp, Oct 26, 2010.

  1. MikeJohns
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    MikeJohns Senior Member

    POR 15 is just another Polyisocyanates Polyurethane 2 pot paint. Marketed as a magic bullet in small pots for large amounts of hard cash :) High cost expensively marketed paints always have an industrial equivalent that costs a fraction of the price and is identical chemically.

    Advantages of thin paints is that they run into the cracks and crevices and supposedly seal off the rust from further moisture ingress.

    There are also 100% solids thin watery epoxies that are targeted for the same application, they all work the same way providing a moderate penetration, but no more.
    Forget the oxygen , it's the water and chloride ions that are the worst offenders. So if you are buying time it's most important to remove all scale then drive out all the moisture and then apply your low viscocity coating.



    Not sure what you mean about the "area between riveted plates" but if you mean the typical corrosion in the overlap there is only one solution and that's major surgery. I've been involved with several riveted old hull rebuilds due to rust issues. I'm interested in what type of vessel you have.
     
  2. CDK
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    CDK retired engineer

    Unfortunately it isn't as simple as that.
    The marriage between iron and oxygen is a complex one, especially when traces of chlorine and moisture were present during rust formation. Covering scales with an impermeable paint layer still allows chemical action from oxygen present in the scales.
    There are at least 16 ways for an iron atom to attach to hydrogen and oxygen.
     
  3. brian eiland
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    brian eiland Senior Member

    Both very interesting replies, thanks.

    I just happened across this simplified pictorial presentation that emphasizes PREPARATION...not converters. ...for what its worth
    http://www.thecoastalpassage.com.au/rust-paint.html
     
  4. cgoodwin
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    cgoodwin Junior Member

    What is the industrial equivalent?

    POR-15 is a single part paint, not a two part and being polyurethane it is moisture cured so in theory sucks the residual moisture from the substrate. I have used it extensively in automobile restoration and in one application, the headlight bucket of a 1972 911 targa, I wire brushed the rust as clean as possible, applied two coats of POR-15 then dusted with a spray primer while still tacky and finally with a spray paint over the primer. That was in 1988 and three days ago I pulled that lamp to replace it and the bucket looks just as it did when I finished it 23 years ago.

    Not saying that this is the same application as say the bilge of a boat but assuming that there is no chipping of the paint I am not sure what the difference would be.

    It is simply not possible to reach all the areas of an old ship and although they did the best they could in 1952, the treatments and paints were not so good. Riveted hulls in particular as the Red hot rivet exposed to air was beat into the hull and the heating alone brings carbon to the surface and promotes rust. There are areas in my bilge where washing with pressure and trying to clean with a wire brush was the best that could be done. After rinsing, ospho, rinsing, rinsing, brushing and vacuuming I coated with POR-15 followed by a primer while the POR-15 was tacky and finally gray Bilge Kote.

    There are other inaccessible areas I am considering soaking with POR-15 using a bug sprayer.

    [​IMG]


    [​IMG]



    56' 1952 Feadship, the oldest Feadship afloat, hull #7. Riveted plates below the waterline, welded above.

    [​IMG]

    [​IMG]
     
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  5. brian eiland
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    brian eiland Senior Member

    Nice Looking Vessel
     
  6. brian eiland
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    brian eiland Senior Member

    Restoration of Old Feadship Yachtfisher

    WOW, I just found your subject thread on this vessel and its restoration over HERE:
    http://www.yachtforums.com/forums/feadship-yacht/8490-53-feadship.html
    What a marvelous story, and links, and photos !

    I loved this quote of yours:
    "It has been 3 long months working every second I could find while still maintaining a business and family. I went through 2 carpenters, 5 painters and 2 welders and ended up being helped by a 54 year old painter and a 52 year old welder becasue not one of the younger people I hired would work or even show up consistently for that matter. Strange world where you drive to work past a half dozen young able bodied men sitting on milk crates begging with cardboard signs, yet can't find people to come to work...

    I have paint in places I can't reach to wash, so much grinding dust in my skin that when the rains came I turned orange, I have a permenant blue dot in my view from my helmet not darkening in time, and get confused if I do not smell like bilge water, burning steel, diesel fuel and paint...."
     
  7. brian eiland
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    brian eiland Senior Member

  8. MikeJohns
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    MikeJohns Senior Member

    [FONT=&quot]

    urethane alkyds or one-pot polyurethanes
    [/FONT]

    I wouldn't count on a single pack moisture cure absorbing much moisture, the moisture just triggers the icocyanate to react with itself and atmospheric humidity is all that's required to do the job.

    The single pot versions aren't as good as the two pot mixes but just look for the urethane alkyd gloss paint. Brands will be different but the products are always the same ingredients. There's no magic with paints, no secret formula. You can ask your local reputable paint manufacturer to recommend an equivalent. It'll work just as well.

    Notes:

    Urethane Alkyds don't like any acid or immersion.
    I made my thoughts on acid known earlier. My feeling is that if you ever use acid then neutralise it with something like builders lime, then wash it off, remember water doesn't neutralise acid.

    Acid is the enemy of steel any acid 'activates' a steel surface while alkali passivates it. In fact you can't get steel to corrode in a reasonably alkaline environment.
     
  9. cgoodwin
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    cgoodwin Junior Member

    "Hi Cgoodwin,
    Just wondering if you have ever looked at these relatively newer Polyurea products.

    Rubberised paint for steel decks?

    polyurea hull spraying video"


    Wow, thank you. Funny that, I have been joking with friends about painting the whole hull with "rhino liner" which, as it turns out, is polyurea. I will experiment with it and do more research, thank you.

    As durable as it appears, it's use does not address what to do with rusted steel other than blasting to white steel before coating...
     
  10. cgoodwin
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    cgoodwin Junior Member

    Well... Playing the devils advocate.

    I weld stainless everyday, after welding I use "pickling paste" which is an acid, (nitric and hydrofloric) to clean the weld, neutralized with water. Phosphoric acid is used to clean boilers and heat exchangers

    http://www.northstarchemical.com/prod_phosphoricacid_prof.htm

    And acid treatment is a part of the process of working with steel.

    http://en.wikipedia.org/wiki/Pickling_(metal)
     
  11. brian eiland
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    brian eiland Senior Member

    You might also join this discussion over HERE...as the fellow "PAR" seems to be quite knowledgeable about such products.
    http://www.boatdesign.net/forums/metal-boat-building/rubberised-paint-steel-decks-36414.html
     
  12. MikeJohns
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    MikeJohns Senior Member




    Yes I know but these are quite different application to cleaning a rusty surface prior to painting inside a boat hull. It's problematic and specifically advised against for good reason.
     
  13. Northman
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    Northman Junior Member

    Mike,
    I have just looked at a 12 year old steel boat. The paint job inside is generally in good condition, but will need to be touched up in some spots - see picture.
    What would your choice be for repainting these spots from (hopefully) bare steel to final coat?
    Regards
    Walter
     

    Attached Files:

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  14. MikeJohns
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    MikeJohns Senior Member

    Walter
    I'd use a Polyamide Epoxy especially in the wet bilge.
    It looks pretty good to me but they didn't use a zinc rich base coat which would have helped.
     

  15. cgoodwin
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    cgoodwin Junior Member

    I am still not sold on the fear of acid. Nearly everyone cleans steel with acid after welding, the metal is then rinsed well, primed and painted or in the case oif stainless, often just acid and rinse. So why is this so different from cleaning rust from older metal, rinsing and painting.
     
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