preparation of interior rust on steel hull

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

  1. NZ_Shipwright
    Joined: Sep 2010
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    NZ_Shipwright Junior Member

    Hi, Sandblasting is the best way yes but this way I suggest is a reliable long term option . I know this as fact.

    We use Protective Paint as a Supplier in link above , They are a Major supplier here
    and you are saying is just nonsense.
    Dont bring any comment foward about my qualification either you dont know me
    but from what I have read here and from previous posts you dont have a lot to offer.It is pretty safe to hide behind your supposed "standards view" but in the real world coal face experience is better than textbook smart.
  2. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Landlubber is a shipwright, leave him alone, he's one of the members who does know his stuff on this forum, and he's bright enough to take advice.

    As for textbook smart so far you haven't addressed my comments as to why acid is considered a poor option on a ships hull in the context we are discussing. Nor anything supporting your view that it's anything other than a poor choice.

    So far you found a couple of application notes which you posted above and an excerpt from a general publication. That doesn't make a case for anything, cleaning and painting metal parts is not cleaning and painting a ships hull.

    Here's the professional approach that would actually mean something: Get a specification from those paint suppliers for a ships hull that they will stand behind that includes the use of acid rust treatment and post it here. You don't make a case by simply claiming you know better therefore your knowledge is superior. I'll eat my hat if you can get them to include acid treatment. Why do you suppose they wouldn't?

    Qualification has nothing to do with it, sensible practical knowledge is everything. Funny that you should be so touchy on the subject of qualification that wasn't even raised.
  3. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Hey mate, "It is pretty safe to hide behind your supposed "standards view" but in the real world coal face experience is better than textbook smart."...try telling that to a prospective customer that is having a steel boat made to survey have too be joking IS the standards that we build to, not some precincieved idea that may or may not be right.....

    ....sorry i called you a shippy...I figured that you were one by your name......touchy little fella aren't you.
  4. michael pierzga
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    michael pierzga Senior Member

    Landlubber, of course the proper standards appraoch is correct when building a boat or pro refitting, but the problem is that this thread was started by a guy name Pete Owne up in Ireland with a bit of corrision and old age in his forepeak. Incredible how the thread changed subject and confussed this poor fellow . Sure hope poor pete didnt go out and purchase a sandblasting rig to "white metal" prep his forpeak for another couple seasons use. Its the problem with forums.
  5. apex1

    apex1 Guest

    The problem is, that you still not got it! As always.

    Do you think a acid treatment on the ballast-insulation boundary, would be a sensible solution?
    Who told you he wants only to get a few more seasons out of the boat?

    In opposition to you, I hope he DID get the guys with the blasting equipment, or at least did use the angle grinder and the wire brush, as recommended.

    If one says "Phosphoric acid" when it comes to rust removal/protection on ships, he will probably get a ice cold shower in the commercial world. One of my oldest Friends is the founder of the largest coating company in Europe, he laughs his socks off when you tell him you prep the boat interior with acids. Is another good job in the near future.
  6. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    NZ shippy, from the Altex sheet that you provided...
    "Recommended Uses:
    • Rust Wash may be used on mildly rusty steel surfaces
    in order to dissolve and convert the rust layer before
    painting commences
    • Surface rust only, can be treated in this manner".........

    ...I am very familiar with Altex, just love paints that you can use...they make this product as do others to provide a service and competition to the other companies that make, basically the same product, it is designed to do what it is not a product for the proper treatment of rust, sandblasting to white metal is the only know and proven method for protective coating of steel in the marine environment.

    I do not mean to be picking on you at all mate, sorry if you feel that I am, but as a professional, and if you are using the name of one, i can assume that you are (reasonably), then we should be promoting the best way to do a job.

    That does not mean that we have to ONLY do it this way, but surely we are obliged to do the best we cam always.
  7. NZ_Shipwright
    Joined: Sep 2010
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    NZ_Shipwright Junior Member

    Hi, Ok let me just say I have never stated that in the commercial world that acids are used for this application. I said ships are designed with a corrosion factor as we know. The accepted standard is by chipping, needling, buff cup on a grinder them prime/paint. If anyone wants to talk shipbuilding or repair I would love to also, however this original post from owensp is what I answered. Nothing more.
    Small yacht with surface rust ..
    In reasonably tight and hard to get places like what was mentioned I believe the use of an acid wash viable after wire cup buff. I believe the phos is also neutralizing the alkaline salts remaining in the small pits and magnetite. Wash maybe a bit better than just fresh water, I agree.Maybe to improve this by using a slight alkaline type wash to neutralize the acid to keep the balance on the plate.
    We use phos , it works , its not everyones cup of tea.

  8. Landlubber
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    Landlubber Senior Member

    NZ Shippy, Yep no worries mate, sometimes that is what is required because of circumstances.
  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    In the tail of this thread there is some concern about acid being trapped in pits and corners.
    I do not think that's what happens.

    Yesterday I removed the rust from a piece of square tube using hydrochloric acid and a paint brush. Not something I'd recommend in a boat because the fumes may shorten your life dramatically, but in the open that is not an issue.
    HCl works much faster than phos: within 5 minutes all black and brown oxides were removed. The greenish brown liquid dripping from the object is not HCl but Fe2Cl3, which is a salt, plus H2O formed by the oxide reduction. HCl, even diluted, reacts violently with the limestone we call gravel here, but the green ooze doesn't react at all.

    The chemical reaction with phos is more complex because the acid already contains some oxygen and several phosphorous iron salts can be formed, but as long as there is iron available, the acid will keep reacting until it has neutralized itself.

    I also observed that with acid, you achieve a white metal surface, but only as long as you continue the treatment. The moment you flush with lots of water, the highly reactive surface turns brown again, so even if the paint can is standing next to you, you still have to wait for the surface to dry and rust will be formed before the first brush stroke. That makes painting over bare metal an illusion.

    In my case, I traded an uneven crust for a thin layer of newly formed oxide, on which I sprayed CR zinc, to be followed by polyurethane. It certainly looks better now than the pieces I cleaned with a flap disc and wire brush, but the long term effects depend on sealing the surface with a paint layer.
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  10. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Painting over rust, an anecdote

    Searching for certain paint properties I arrived at this website:

    In the early sixties I was in the advertising business, mainly technical accounts and Zandleven was one of our clients.
    They had nothing to offer for the average garden gate, but provided solutions for offshore drilling platforms, concrete silos, bridges and even produced a 1200 C. marker paint for steel forgeries. There products were sold in drums rather than cans.

    But they wanted to increase their market share and hired us to achieve that. We designed the company logo they still use, prepared technical documentation and advertisement.
    I was briefed by the research manager, who told me that some of their products contained rust inhibitors and provider lasting protection even when applied over rust. Because rust removal is the nasty part of painting, I saw excellent opportunities there.

    I translated that into sales talk and used words like breakthrough and unbeatable performance. When I presented our work at the next board meeting I was met with unexpected hostility: the company president doubted my sanity. Painting over rust was unheard of in these days.
    The research manager didn't back me up but said there might have been some misunderstanding about the rust inhibitors that were only there to take care of the residual rust after blasting. Texts were watered down to mediocre or completely rewritten. In fact there was so much commotion that several other items were passed without proofreading later and were printed with annoying typos, so we lost the client.

    Now, 50 years later, I see they still want all steel to be blasted with non-metallic particles, even when zinc coated.......
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  11. Conachair
    Joined: Jan 2009
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    Conachair Junior Member

    Peter, best literature regarding steel boat maintenance in the real world I've found is here...
    Cheap download.

    Best 1st coat sealer I've come across is the one recommended in that book, ameron amerlock sealer -
    Then amerlok 2 high build epoxy on top of that, the sealer goes off very slowly and soaks into absolutely everything while the high build goes off quick, on a hot day you might get 3 coats on.
    To add fuel to the acid etch, assuming blasting to 2.5 is not possible there seems to be the choice of treating the steel with phosphoric acid or painting over an area where there is still rust in the pits. Without blasting I've yet to find a system which will completely remove rust from the pits, the area will look perfect but put some opsho on it and all the pits will bubble way as the rust gets converted.
    So in my mind the question is will the paint system be more likely to fail painting over rust or painting over iron phosphate. Phosphoric acid etch has worked well for me so far, but I haven't got 10 years spare to try both side by side in a hidden area of a rusty bilge :)

    Once the paint is on keep the water out! :)
  12. castaway
    Joined: Nov 2010
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    Location: Solent UK

    castaway New Member

    Bruce Roberts Owners Group

    Hi Peter

    I think we may have discussed this a while back, but maybe not.

    As there does not appear to be any sort of 'unofficial' Bruce Roberts Group, Club or Web page, and as BR him self doesn't appear to interested in owners who are not purchasing his plans, I have set up a little BR Owners Group on Yahoo.

    Its only been up for a couple of weeks but is attracting a steady drip of new members.

    No commercial links and the intention is only for the general pleasure and enjoyment of boat ownership.

    All best, Nick [Mauritius 43 Theseus]
  13. Jack Hickson
    Joined: Jan 2011
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    Location: Vancouver Island BC

    Jack Hickson New Member

    I once used Epiglass phosphoric acid based prime on steel . The epoxy over it fell off in sheets. Friends tried international phosphoric acid based primer. Same result. Haven't seen any other result.Only sandblasted steel works.
  14. mastcolin
    Joined: Jun 2005
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    Location: The Netherlands

    mastcolin Senior Member

    I am pretty sure that product is for aluminuim not steel which would explain problem perhaps.

    On separate note in response to some above posts, note that cars are made with cold rolled steel plate. Marine steel is hot rolled. It ain't the same. (they don't blast cars before painting do they?)

    As foreman-painter and ex-tech service and laboratory for International Paint (the world's biggest supplier of coatings for steel), acid washes are not recommended. You just can't guarantee a clean surface, clean as in acid free. And the surface it leaves behind is of questionable technical benefit anyhow.

    Anything less than cleaning to Sa2.5 or St2 minimal is less than satisfactory and depending on extent of corrosion remaining you will always be touching it up. Yes you can do it otherwise. whether it is worth the risk is, in my (the marine world's experience) very debatable.

    As has be pointed out numerous times above, if there was a magic potion, it would be being used and 1000 of millions of hours blasting would be being saved.

    Another important point to note in the painting of these awkward areas is that a) ensure you have sufficient ventilation. Trapping solvent in cured coating is not good idea b) make sure you try to paint in optimum temperature envelope ie between 15 and 20C. The paint cures best and you minimise risk of solvent entrapment.

    It goes without saying that it is good idea to make sure you take care with film thickness - a reason bilges often fail is that the paint is TOO thick in the nooks and crannies. It tempting to use the 1st coat as a filler in all the weld seams and corners. Try to avoid.

    The 1st coat is the most important coat. This is where you get the adhesion. Optimise this and you have more leeway on the coats on top.

    Lots of thin coats are better than 1 thick coat.

  15. cgoodwin
    Joined: Mar 2011
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    Location: Seattle

    cgoodwin Junior Member

    Wow, that was a painful read, why all the name calling and infighting?

    Ok, in the real world there are areas that can not be blasted or wire brushed, what then? Sat you have a 60 year old steel boat and areas of the bilge are below the floor, in areas inaccessible, you can remove the scale but not blast or brush clean? What about the area between riveted plates? And why has no one addressed the question about Por-15?

    It seems that in order for rust to continue it needs O2 and possibly coating would prevent O2 contact...
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