Over coating coal tar epoxy

Discussion in 'Materials' started by rfleet1066, Oct 24, 2012.

  1. rfleet1066
    Joined: Feb 2012
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    rfleet1066 rfleet1066

    Is it necessary to top coat coal tar epoxy, or can it be left as is?

    I am doing a riverine camo paint job and black will be one of the colors.
    I'm wondering if the c/t will resist the elements all by itself.


    Ryland
     
  2. michael pierzga
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    michael pierzga Senior Member

    When you overcoat Coal tar epoxy the BLACK bleeds thru the paint...nasty stuff.
    Perhaps they make better, non bleeding coal tar, but Im not aware. Why coal tar ?

    If I want to make epoxy black I add graphite powder then overcoat with a clear UV resistant coating. Seems to hold up reasonably well. The sun, black colours and epoxy are not friends.
     
  3. rfleet1066
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    rfleet1066 rfleet1066

    coal tar epoxy

    I am painting the hulls with coal tar epoxy for corrosion resistance. Also the bridge beams and other steel above deck, with a thin coat of zinc chromate first.

    Ryland
     
  4. Frosty

    Frosty Previous Member

    Zinc Chromate with coal tar epoxy --exellent system . I guess you have been advised by Joton who swear by this.


    Over coating coat tar should be done withing 24 hours if possible to get the molecular bond ( bleed though) I assume you are talking anti foul. Bleed through is good, just give it another coat.

    If your not then Jotumastic 87 in silver is surface tolerant which means it will stick to most surfaces if you cant get it clean and is excellent interiour paint for bilges.
     
  5. pauloman
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    pauloman Epoxy Vendor

    generally you cannot topcoat coal tar epoxy, especially if it is weathered. It is the big disadvantage of coal tar epoxy (well, maybe cancer is bigger). Coal Tar epoxy is used less and less - although I still sell a high end version

    paul oman
    progressive epoxy polymers
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've had some success with aluminized paints. This might be a good test for for one of your products Paul (I received you package BTW). In previous applications, I used regular aluminum paint and after several coats, it did seem to lock down the tar. I've also used elastomeric (again aluminized) paints with mixed results, probably from film thickness issues.
     
  7. gonzo
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    gonzo Senior Member

    If you are doing a camo paint, bleed-through is not much of an issue. The staining may make the boat more inconspicuous.
     
  8. Frosty

    Frosty Previous Member

    Its camouflaged if you not sure and its not what he was asking . Please try to keep the question in focus.
     
  9. pauloman
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    pauloman Epoxy Vendor

    the problem is that as the epoxy breaks down it releases some of the 'tar' and you cannot paint over 'tar'. That said, I've had one boat yard owner use my coal tar epoxy on this boat bottom and then topcoat with bottom paint without issue. Of course, it was fresh epoxy and high end coal tar epoxy. However, I have 'tested' my coal tar epoxy with a topcoat of varnish and it was a mess!


    paul
    progressive epoxy polymers inc.
     
  10. gonzo
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    gonzo Senior Member

    Are you trying to protect the epoxy from UV damage? I assume the rest of the areas will be painted with browns and greens.
     
  11. rfleet1066
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    rfleet1066 rfleet1066

    overcoat

    I certainly want to protect the epoxy from UV, as well as the steel from corrosion. Out of ignorance, I have painted the vessel above the waterline as it was constructed. First a wash with soap and water, a rinse, wiped down with thinner, the a thin coat of zinc chromate followed by the coal tar epoxy. From the water line down, I will blast to white metal, zinc chromate, coal tar epoxy, then anti-fouling paint. Again, I am armed only with ignorance and a dream.

    Ryland
     
  12. gonzo
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    gonzo Senior Member

    Camo paint is flat and covers a lot of blemishes. The paint used on roads for markings seem to be UV resistant and extremely tough. White, blue and yellow are the most usual colors, but you can probably tint them. I have never seen bleed-through on asphalt road markings.
     
  13. michael pierzga
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    michael pierzga Senior Member

    Not to change the subject of coal tar but since you are in Virginia with its gigantic concentration of Navy ships, you should investigate LSA paint for your camo job.

    http://www.paintdocs.com/webmsds/webPDF.jsp?SITEID=STORECAT&doctype=PDS&lang=E&prodno=N40A200

    LSA Low solar Absorption paint in required by the military. It drastically reduces the heat buildup on the surface of a structure caused by flat or semigloss finishes exposed to the sun. Heat is the enemy of steel, epoxy coatings.
     
  14. rfleet1066
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    rfleet1066 rfleet1066

    Blemishes are part of the art. Work boat finish standards are applied on this vessel. Clearly a finish that endures time is desired.

    Ryland
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Paul, would it be possible to over coat the coal tar with straight laminating resin, then paint as usual?
     
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