Priming and painting Epoxy

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

  1. michael pierzga
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    michael pierzga Senior Member

    There is more paint on the inside of a boat than the outside. Working with two part paints inside a hull is hazardous to your health.

    It would be wise to check out the new waterbased marine paint systems for interior work. Purchase a quart of primer and topcoat , then practice to see if this waterbased paint is workable. An important feature for interior paint work is FAST DRY.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I haven't been around for a while and would like to dispel some misinformation I've seen in this thread.

    You always apply paint in thin coats and it doesn't make the coating weaker. In fact, it's the only recommendation from any professional or paint formulator.

    A professional or wise novice will always use a primer, even on fresh epoxy. Technically, you can skip the primer and likely have no adhesion issues, except with some alkyds and modified alkyds, but this isn't the only reason you use a primer. Primers serve several functions and one is to provide a final, easily abated surface, for final fairing and smoothing. With several coats of primer (most is sanded off), possably in different colors, so you can keep track of progress, you can fine tune a crappy paint job into a good one. It's all about the prep, not the top coat.

    A good primer base will even the surface, so the top coat will lay down uniformly. It also acts as a bond coat, marrying the substrate to the top coat. Because primers have silica and other fillers, you can quite precisely "hone" the surface to a baby's butt result.

    A big mistake, especially with hand applied primers, is to under tooth the material. By this I mean, you can use too fine a grit on primer which will ruin it's ability to grip the top coat. 220 is more then sufficient, 280 way past what you can see and 320 pushing your luck to the point, that you can have some lifting issues in hard top coat use. The only time this isn't rue is when spraying hi end finishes, such as LPU's. Top coats will easily cover and fill in a 220 grit sanding marks. If not, you haven't sufficient film thickness and you should apply more coats.

    Top coats can tolerate these extra fine grits, particularly if you're continuing the smoothing process, such as compounding and polishing, but this is typically well outside the realm of the novice painter.

    Roll and tip techniques aren't dependent on thinning your paints, but are a function of the modifiers, now used in most modern paints. 20 years ago, you couldn't do this with paint, no matter how much thinner you used, but today, paints are far better and roll and tip techniques are now possible. You can pull a can of Brightsides off the shelf and have nearly flawless results, straight from the can, assuming prep is sufficient and the conditions are well suited to the task. Again this assumes hand painting, as spraying almost always requires you thin just enough to remove stipple.

    To directly answer Myboatbuilder's questions, if you want a really high end paint job, you'll have to pay for it in both product and effort. Sprayed LPU's dominate this area and getting them to look like a mirror, requires the surface to be really fair and smooth. You can paint a poorly finished surface with these paints, but you'll instantly wish you'd put a lot more time and skill into the prep.

    Good paint jobs are 90% prep and 10% actual paint brush or gun in hand time. If you want a mirror, you have to massage the surface to a suitable level, which frankly is well past most novice painters. A roll and tip job can rival a sprayed paint job, with much less trouble, but again the surface will reflect each and every flaw that was over looked in prep.
     
  3. CatBuilder

    CatBuilder Previous Member

    Par, thank you for that post. I'm still learning about marine paint and it was very helpful to read.

    Question:

    If you have a faired surface of microballoon/epoxy fairing compound, what is next? Neat epoxy sealing coat, then primer, or can you go straight to an awlgrip 535 high build primer?

    At this step, going from microballoons to primer, are the steps any different for above and below the waterline?
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Seal it, particularly with balloons. This also offers a final, last fairing surface to really smooth things out and provide a uniform, toothed surface for the primer. If you're experienced with fairing and smoothing, you don't need a high build primer, but if you still need to fine tune the surface, then you'll go through several coats of high build, before top coating, knowing you'll knock 80% of it off with fairing and smoothing operations. I always do 2 final primer coats, once satisfied with the finish quality, so I know there's sufficient film thickness under the top coat on the whole hull. Lightly sanding between coats.

    Fairing and smoothing operations are the same, regardless of hull location. This said, you can be less annal about underwater areas, as these will be out of sight. A racer might do the reverse, with a really sweet, symmetrical bottom, but topsides that are just okay.

    Both fairing and smoothing is an art form. Once you figure it out, it's a lot easier, but most can't find fair or smooth until they get some shinny stuff on, which of course is way too late.
     
  5. mastcolin
    Joined: Jun 2005
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    mastcolin Senior Member

  6. CatBuilder

    CatBuilder Previous Member

    Great info! Again, thank you, PAR. Learning a lot here.

    One more follow on:

    I have an epoxy that should be post cured as the main laminate. Above this, as a fairing layer I have used an epoxy that doesn't require a post cure.

    What do I do?

    Will the extra "no post cure" epoxy fairing and sealing coatings outside the "should cure" epoxy in the glass weave take care of any possible print through?

    Or...

    Will the "should cure" epoxy below start to move in the hot sun some day and move the "no post cure" epoxy around, causing a mess?

    With different Tg's and only one having a post curing schedule, I am certainly hesitant to post cure the whole laminate, possibly ruining the outer layer of "no post cure" epoxy.

    I think this is what they refer to as, "painting ones self into a corner!" ha ha ha ;)
     
  7. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    It would be the perfect world if you could post cure EVERYTHING. Even the final paint film. With Awlgrip flag blue...Pro applied to a mirror finish inside of a climate controlled build shed in the Netherlands.......I can see 340 grit sandpaper scratches in the surface of the flag blue after it has post cured in the sun for one season.

    You would be best to...use good craftsmanship, paint the boat WHITE , not be anal about coating perfection, then two years down range when you re paint, pull any post cure offender out with a board sander.

    The paint cycle on an industrial yacht is 3 years, depending how many times you bounce off the dock or the tender bounces off you

    Post cure is barely visable in white.
     
  8. CatBuilder

    CatBuilder Previous Member

    I can post cure the entire boat at one time, if that's any help....
     
  9. michael pierzga
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    michael pierzga Senior Member

    I dont know...all vessels Im involved with are to big and complex to post cure.


    The local custom builder postcures small craft... then primes , topcoats and collects his fee.
     
  10. CatBuilder

    CatBuilder Previous Member

    I'm 15 meters loa x 7.5 meters beam. I can post cure the whole boat if needed, but do I need to?

    My boat is certainly too complex, as described above...
     
  11. AndrewK
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    AndrewK Senior Member

    Yes you should post cure.
     
  12. CatBuilder

    CatBuilder Previous Member

    But at what schedule if one epoxy doesn't require it, the second has a schedule, and the last doesn't require it? They all have different Tg's as well.

    Can't I damage the non post cure epoxies by taking them up in temperature?
     
  13. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    Every epoxy will benefit from pos tcure, you will not damage the ambient cure epoxy.
    If you do not post cure the infusion epoxy you may have as much as 10% unconverted material.
    What schedule; you do not need to worry about this in a simple uninsulated plastic tent you will only get to ~60'C.
    Because the structure will not be supported in a mold you need to bring the temperature up slowly and keep it 5-8'C below the HDT. ie you push your HDT up rather than pull it up.
    Your laminates made with the epoxy requiring post cure will have a HDT ~50'C when not post cured. So start the heat cycle at 40'C and raise it slowly to 60'C over 24hrs., then keep at this temp for a further 12hrs.
     
  14. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Paint System


    A paint system approach. He is absolutely right. It may cost more money but that is the only way to match sure you don't get some surprises.
     

  15. CatBuilder

    CatBuilder Previous Member

    Well that's easy enough. 60C is nothing to get to in the summer here. I should be able to get the whole boat to 60C (will have to check HDTs to be careful) It's already above 40C in the tent naturally some days! :D
     
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