Steel hull prep - Sand blasting VS Wire wheel

Discussion in 'Boatbuilding' started by parkland, Feb 17, 2013.

  1. parkland
    Joined: Jul 2012
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    parkland Senior Member

    I'm reading about the application of coal tar epoxy, and the 1st most important rule is to prep the metal by sandblasting.

    Would a powered wire wheel provide the same effect though?

    I might end up re-painting a boat that isn't right in my back yard, so it would be a lot more practical to not have to haul bags and bags of sand blasting media.

    The boat in question doesn't really have a rust problem, this would be to mostly tear off the old paint and re-do with fresh coal tar epoxy.
    There is the odd bit of rust, but nothing major at all.
     

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  2. Submarine Tom

    Submarine Tom Previous Member

    I blasted my hull with baking soda.

    It's not as heavy as sand.

    Of course mine was a fg hull not steel.
     
  3. parkland
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    parkland Senior Member

    Probably 100x times more expensive than sand too haha.
     
  4. pdwiley
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    pdwiley Senior Member

    There are dozens of threads on this.

    If the boat is already painted and the paint is reasonably ok, then no you don't need to take it back to white metal. Depending on the paint, good luck trying to cut it with a wire wheel. Jotun 605 for example takes a lot of work to get off.

    If it's plate covered with mill scale you're going to die of old age before you get even a fraction of the mill scale off with a wire wheel.

    I hate sand blasting so I paid a company to do all of my plate & bar *before* I started welding the boat together. My 120 cfm setup is fine for small bits but even that is far too small to do the entire boat - at least it is if you're as impatient as I am.

    PDW
     
  5. Yobarnacle
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    Yobarnacle Senior Member

    Water blasting is done on steel hulls n commercial yards. A light rust film is deliberately allowed to form before epoxy primer is applied, for greater adhesion.
    Think of it like gun barrel blueing, a chemical rusting process resulting n a protective coatng. :)
     
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  6. michael pierzga
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    michael pierzga Senior Member

    Simply google metal preparation and you will find countless studies concerning metals.

    SAND BLAST.


    Locally I can hire a Pro blaster for 70 euros per hour, plus materials. This blaster can sweep the entire bottom of an 80 foot steel hull, keel and rudder then apply one coat of epoxy primer in 50 hours.

    Dont play games..get a blaster.

    To save money have the complete work area prepared for the blaster...scaffolding, lighting, ventilation surface protection and clean up
     
  7. Submarine Tom

    Submarine Tom Previous Member

    No, it was cheaper, ha ha.
     
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  8. parkland
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    parkland Senior Member


    Wow I didn't see that coming.
     
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  9. Submarine Tom

    Submarine Tom Previous Member

    The guy was new to the industry, I had an influential job at the time, so he gave me a good price.
     
  10. Submarine Tom

    Submarine Tom Previous Member

    What aluminum does quite naturally.

    Cheers!
     
  11. FMS
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    FMS Senior Member

    I was advised to primer aluminum quickly after acid etching for strongest adhesion. The natural protective film on aluminum does not improve adhesion of surface coatings.
     
  12. FMS
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    FMS Senior Member

    cost of soda blasting

    More or less than $30/foot?
     
  13. parkland
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    parkland Senior Member

    According to his post, and my math, 43.75$ / ft (euros)
     
  14. Submarine Tom

    Submarine Tom Previous Member

    That is correct.
     

  15. Submarine Tom

    Submarine Tom Previous Member

    It was $1.07CAN per square foot. And he did a great job.

    The objective was just to take the gelcoat off below the waterline so I could apply an epoxy barrier coat.
     
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