Rustproofing inside steel hull with tar

Discussion in 'Boatbuilding' started by parkland, Nov 16, 2012.

  1. parkland
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    parkland Senior Member

    I'm just curious if the inside of a steel hull was painted with a roofing type tar, if it would prevent rust?

    I painted some outdoor steel stuff I have with aluminized tar for patching camper roofs, and the steel has zero signs of rust, and the bare metal is flaking and rusty.

    Seems like it worked very well, and cheap.

    Would the aluminum in the tar react with the steel?
     
  2. rasorinc
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    rasorinc Senior Member

    Do not forget to allow for preventing condensation under your coatings.
     
  3. parkland
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    parkland Senior Member

    How would you get condensation under a tar coating?

    Is the only reason we don't see more tar simply that it's messy?

    Seems like it would be the best rust proofing ever for in the hull.
     
  4. sdowney717
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    sdowney717 Senior Member

    Roofing tar idea?
    Although It likely will harden then crack and the steel will rust.
    And be an awful mess if you have to do any welding repair to the hull, boat will go up in flames.
    It might also stink and make you feel ill. Could even make you sick from fumes, maybe.
     
  5. parkland
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    parkland Senior Member


    The stuff I tried didn't flake, but even if it did; wire brush and a shop vac, and apply another coat.... seems almost too easy.

    Also saves the step of prepping the steel for paint, it's usually covered in black protective grease of some type.
     
  6. Wynand N
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    Wynand N Retired Steelboatbuilder

    and assumption is the mother of all screw-ups....

    Any paint or covering is only as good as its preparation. Even when using decent coatings such as epoxies, it will be a worthless exercise if the surface was not prepared by taking rust, mill scale etc off by shotblasting before applying the coating.

    That said, nothing is new in boat building and since steel boats are around for more than 100 years, tar would have definitely being used in the early distant past of steel boats because that was what was available at the time except some primitive paints.

    Since it is not used for many decades now you need to answer the question why? You will probably find that the main reasons are those few raised by sdowney717.
     
  7. parkland
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    parkland Senior Member


    Why would you waste time cleaning off protective protective oil coating, when you're about to apply a protective oil based coating?

    I can look where I put it, it even "seeped" oil onto the bare metal; what more could you want?
    And stuck on there tight enough you need a razor to shave it off.

    I could agree with the smell and fumes, it stinks for a good week, but after that it doesn't smell much. I suppose it would depend on the temperature too.

    This is the aluminum patch tar I speak of, not black tar.

    I
     
  8. michael pierzga
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    michael pierzga Senior Member

    With steel boats much depends on the environment you operate in.


    Fresh water is gentle so less than perfect solutions work.

    Salt water is aggressive and can defeat even the best protection.

    Boats like canal boats in England or the Netherlands operate in gentle conditions and use many Home Brew solutions to good effect. Lanolin for example
     
  9. parkland
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    parkland Senior Member


    Ahhh....

    So what you're saying, is that if it's in fresh water, cheap solutions might work just fine... ?

    But on the inside would be the same.... condensation.?
     
  10. michael pierzga
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    michael pierzga Senior Member

    Pay your money, take your chances.

    Once the interior and systems are fitted to a steel boat, repairing any " chances" becomes extremly expensive or impossible .

    Tar sounds like a nightmare.

    Surface tolerant paint for steel is the best second choice if the steel structure cant be sandblasted .

    Speak with your paint supplier.

    Google canal boats and learn what old timers did to protect steel
     
  11. gonzo
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    gonzo Senior Member

    Tar has some problems like being soluble in motor oil and fuel. Any spill will make a sticky mess. Also, it becomes soft and sticky with heat, a problem under decks and inside enginerooms. Another problem is that it is very flammable and creates a fire hazard.
     
  12. goodwilltoall
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    goodwilltoall Senior Member

    Cement is a better and cheaper inhibitor of rust than tar.
     
  13. michael pierzga
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    michael pierzga Senior Member

    Sure.. a cement wash works well, Ive treated many water tanks that way, but you cant coat the interior of a boat with it....as soon as you touch it its gone...as soon as the cement is contaminated by bilge goo or beef stew youve got a monster on your hands.

    As they say...do it right or dont do it at all.

    Modern paint systems work and will be 10 times cheaper over the long term
     
  14. goodwilltoall
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    goodwilltoall Senior Member

    There are better coatings than cement but, have seen it perform well with old shovels and wheelbarrows that are coated with it and left outdoors. It doesnt fall apart when touched or contacted with goo, the oily goo might even help it as petroleum based grease will protect bare steel. But petroleum products also break down cement.
     

  15. pdwiley
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    pdwiley Senior Member

    Are you talking about pickled & oiled plate or hot rolled plate with the mill scale still on it?

    Vast, vast difference in how you go about covering it to inhibit rust between the two.

    Hot rolled plate, if you want long life, needs to be blasted and primed. Many have tried to avoid this step. Good luck if you want to be the next failure in the ranks.

    Pickled & oiled plate has the scale off already - that's the pickling bit. Recommended treatment is to wash it down with a good detergent, flush with a lot of fresh water and then paint with oil based paint. Or epoxies.

    Painting the interior is such a PITA that you don't ever want to do it again just because you wanted to save a bit of time and money the first time round. My hull has 3 coats of primer over the weld-through primer then 4 coats of enamel over the primer, and the steel was professionally blasted before I started building. I enjoyed none of this including paying the bill for the blasting, but I'd do it all again.

    I can't think, offhand, of a single book written by a boatbuilder where using tar is a recommended coating for steel.

    Now, if you want to ignore the accumulated knowledge & advice of people who've built steel boats, go for it. You've gotten the advice of the people on this forum, and it's 'Don't do it'. Up to you if you take notice or not, but do us a favour and don't just keep arguing your position because you want to be right.

    PDW
     
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