Priming and painting Epoxy

Discussion in 'Materials' started by mvboatbuilder, Jan 14, 2012.

  1. mvboatbuilder
    Joined: Jan 2012
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    mvboatbuilder Junior Member

    Hello I am building a 18' powerboat ply covered with 10 oz glass and epoxy, i have added 2 fill coats as well. i am thinking maybe one more fill coat but am sort of confused about next step. The boat will be on a trailer but might be on a mooring for a couple of months at a time. I really want to have a high end paint job as well as the best protection for the hull. High Build primers? epoxy with pigments? different steps for above and below the water line? any suggestions would be appreciated Thanks
  2. michael pierzga
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    michael pierzga Senior Member

    Im painting today.

    Build your boat, fair it with epoxy filler , board sand to a high standard, then give the entire hull a coat of pigmented epoxy to seal the porous fairing compound. The pigment is very helpful for building colour. . White pigment if you boat will be white, grey if your boat will be a dark colour.

    Now sand the pigmented epoxy with medium sandpaper...180 0r 220 to knock off the gloss and give a tooth. Next roll on one coat epoxy primer , 545 awlgrip is good,...waite two hours and roll on a second coat of 545 primer. Primer does not brush well..roll it on. Let this two coat paint system cure hard then carefully, gently BOARD SAND the primer with 280 or finer paper. Carefully sand. fine or very fine sandpaper. Avoid sanding thru the primer. Primer sands very easily.

    Next wash the entire boat with soap and water.

    While hull is going from wet to dry', carefully observe the surface for any low spots. They will stand out during the drying cycle. mark these low spots and fill with one or two additional coats of primer...sand flat with a board or block and very fine paper .

    Wash the hull once more with soap and water. Tape off the topsides and paint...roll and brush coat of 35 percent thinned Awlgrip topcoat. Allow to cure then fine sand this first coat with 340 paper and apply the final 40 percent thinned top coat.

    When working inside in a controlled temp , you may be able to reduce the thinner to 30 percent. Try on first coat.

    To get good results the topside paint..awlgrip...must be very thin.

    With best practice the result will be glass like.

    Underwater surfaces need antifoul instead of topside paint.

    Choose a hard antifoul.
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  3. mastcolin
    Joined: Jun 2005
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    mastcolin Senior Member

    All good advice.

    My only comments would be regarding sanding.

    You don't have to sand the last primer coat by board or block. You can use a machine as by this stage it should be pretty fair. You may be even happy with a 3/4 fair hull.

    If you are going to brush/roll the topcoat you had better use fine paper. If you use wet/dry paper the grade numbers are different from the dry type papers. Rule of thumb is that 600 waterproof paper gives the same finish as approx 400 dry type papers. I wouldn't appy topcoat onto anything less fine than 320 dry types unless you are planning on lots of topcoat layers.

    Sanding between topcoat layers will need this finer paper here as well or the scratch marks will show through. Thinks 400 dry between coats. If you roll and tip it good you can just give it a light sand hopefully. It is better to try to get good finish rather than than have to sand out brush marks.

    There are plenty of posts in forum history to give you more background. Happy reading and success.

    ps You can probably use a cheaper underwater primer than the topcoat primer. Underwater doesn't need to be fair. Hopefully your build skills left the hull good enough.
    pps you don't have to use awlgrip system. There are other options. You pays your money and takes your choice.
    ppps "fill coat" do you mean a pigmented coat or just resin? If you have used pigmented coat it may be very pinholey. You perhaps won't see this till you paint. If it does look pinholey before you start. it may be idea to try to fill this with a very wet mix that is pigmented and you can try to squeeze this into the holes using a metal blade (you find them in hardware stores used by plasterers). As I said previous, search history here.
  4. CatBuilder

    CatBuilder Previous Member

    An amazing thread. I was just trying to wrap my head around this stuff myself.

    Any suggestions for the underwater primer and paint before the bottom paint? Or... do you just go from primer to bottom paint?

    Also, any suggestions as to paints that are as good as Awlgrip but that do not carry the "marine" price tag?

    If I'm looking at paints other than Awlgrip (mostly because I want a cooler looking paint job), what do I need to know? What exact paint do I look for?
  5. michael pierzga
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    michael pierzga Senior Member

    Your project is a big new build. You need an entire paint system.

    You would be best advised to seek professional advice from a LOCAL professional paint supplier. Not west marine , not the local body shop.... a marine paint supplier.

    Many good paint systems around.

    Ive had big paint jobs done with several different paint systems and they were all successful. Product support and knowledge are the secret.

    I prefer Awlgrip primers and topcoat simply because I have years of experience with them, they work well with roller and brush , and the local tech support is first class.

    The local shipyard only uses International underwater primers.
  6. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Michael brought something up in passing I want to expound on a little. Anti-fouling paint can be a very local product depending on your water and fouling organisms. So a little local knowledge can go a long way here.
  7. CatBuilder

    CatBuilder Previous Member

    I'm a big fan of Petit high copper ablative anti fouling paint. Works for me from the Keys in FL to the Canadian border. 2 years between haul outs.

    You can tell it's a good copper paint by the weight of the can. A heavier can is more metal inside.
  8. mvboatbuilder
    Joined: Jan 2012
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    mvboatbuilder Junior Member

    Hey thanks for all the great info ....really helps giving me direction to go in hope to get back working on the boat in the next couple of weeks thanks tim
  9. michael pierzga
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    michael pierzga Senior Member

    Last week was a painting week...outside. the Awlgrip topcoat system was worth the cost. I say dont fool around, go with the good stuff.
  10. CatBuilder

    CatBuilder Previous Member

    With all the labor that goes into a paint job, I have to agree. No reason to chance it.
  11. michael pierzga
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    michael pierzga Senior Member

    And 340 grit paper to prepare for finish coat leaves sandpaper scratches. go 400 grit. I can see the paper marks
  12. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    The biggest mistake people make is making coats to0 thick. Thin coats is the way to go.
  13. MechaNik
    Joined: Jan 2011
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    MechaNik Senior Member

    You should check with the supplier on coat thickness and thinning. You may get a good finish on Poly top coats when applied thin but it wont last no matter how many thin coats you have applied (unless it goes on wet on wet). It is a little hard to explain briefly but basically the paint forms a skin that has the hardness/wear properties.
    Acrylics have a lot to offer for beginners, Awlcraft is decent for casual boaters just wont wear as well.
  14. michael pierzga
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    michael pierzga Senior Member

    This is true. When roll and brushing , To achieve the super wet glass look , the paint must be thin. This shortens the life span of the paint. By working in the correct temp " room temp " you can avoid overthining the paint. With awlgrip 30 percent seems to be the limit. Perhaps ask a Pro painter or you paint supplier for advice

  15. pauloman
    Joined: Jun 2010
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    pauloman Epoxy Vendor

    my recommendation as an epoxy professional is to prime with something like a pigmented moisture cured urethane (lpu coating - like aluthane) because epoxies containing nonyl phenol can under certain conditions really slow down the drying of traditional enamels. Also with a pigmented primer you will see flaws in the epoxy layers/topcoat you missed.

    Then topcoat with traditional enamel (or acrylic latex for 'work boats') . 2 part poly coatings (like Alwgrip) cost about $100 a gallon (lpu marine) to $400 or so per gallon. An option is to use enamel and the topcoat/seal with a clear lpu (like acrylic poly UV) which is about a $100 a gallon.
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