outboard primer - zinc chromate vs epoxy

Discussion in 'Outboards' started by swade, Jun 26, 2010.

  1. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    The awlgrip story ( which is all epoxy below the top coat)
    but you could get away with
    alodine ( or whatever chemical is legal) to wash it clean after you have a sanded or blasted it
    545 - you can keep coating this as thick as you want just put your pot in the fridge and keep using it
    filler if needed ( requires 545 over the filler)

    You got the standard answer from the guy
  2. aussiebushman
    Joined: Oct 2009
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    aussiebushman Innovator


  3. apex1

    apex1 Guest

    You cannot leave the Al unpainted in any underwater application, thats a nonsense!

    Blast the surface as mentioned above (soda is my choice), don´t needle, it drives the salts deeper into the surface.
    Use (any) etch primer
    Apply two layers of (any) thick film epoxy. (if need be, have a microballoons thickened layer of neat EP between them for fairing)
    Apply two layers of UV resistant Ep paint or:
    just one and antifouling.

  4. fg1inc

    fg1inc Guest

    Anti-fouling on an aluminum lower unit? Please.... not a copper based anti fouling!
  5. apex1

    apex1 Guest

    Who said copper?
  6. Frosty

    Frosty Previous Member

    If its an outboard it would only be submersed when in use!! It can be washed hosed with fresh water after. No?

    If its a trailered boat even the hull does'nt need anti fouling it can be sprayed with a bit of WD.
  7. swade
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    swade Senior Member

    This isn't about anti fouling, it's about aluminum corrosion protection. zinc chromate is for aluminum, doesn't have copper...generally what's used though other variants zinc phosphate,etc as epoxy additives are around and used now.
  8. swade
    Joined: Jun 2010
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    swade Senior Member

    heh nevermind me, i did not see the subject had changed to underwater protection doh!

    Alan look around sanding blasting my lower unit was pretty cheap (it's not small either off a 130hp), i paid 20 bucks (usd). Unfortunately
    they don't normally do it so i didn't take everything down there and of course mid section would have to be removed or done outside.
    Lower unit was very pitted from previous owner, sand blasted faired filled with epoxy...looks great. Other parts were just surface corrosion here and there.

    Richard are you saying go right over the zinc chromate self etching primer is ok with epoxy primer?

  9. apex1

    apex1 Guest


    And Frosty is right. When the boat sits on the trailer most of his life you don´t even need antifouling on the hull.
  10. swade
    Joined: Jun 2010
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    swade Senior Member

    I decided to go with existing zinc chromate primer, going to cover that with epoxy primer, then follow with a single stage urethane. I have another 50hp to repair and paint on my pontoon, so i went ahead and picked up a used supplied air pump and full mask. Given the cost of full mask and replacing organic cartridges when working with these solvents/ iso paints and that it has residual resale value the supplied air seems a better safer investment.

    Next time i'd probably sand blast everything,much quicker to drop it off for a few bucks with better results i'd think. Though the areas that I didn't have blasted and abrasive / wire wheeled should be ok. Better would be to remove powerhead from the upper case for a 100% job but removing 10 year old bolts from a salt water engine is challenging i've found to say the least.

  11. J3
    Joined: Jun 2010
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    J3 Junior Member

    25 years ago I started with acid wash, then zinc chromate primer. I was using interlux - the acid had a yellow color and the zinc chromate had a metallic pink hue - I don't think interlux had more than one at that time. Then (don't laugh) for a spectacular failure... I thought I could use some black 2-part VC-tar over the primer. It looked great the month it went on. However the heat from the outdrive made the thick coating "tear" off the bullet and crack on the upper when heat built up. Primer held fine. Had to start over the following year with a thinner top cote of trilux II - that stayed clean looking and defect-free for 5 years before it needed repainting.
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