Spraying mold plug with Duratec questions

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, Jun 10, 2021.

  1. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    OK guys back at it a few year later and I final bought an air compressor to practice spraying some projects

    It was actually easier than I thought to spray but I have a few questions...

    I am struggling getting a nice finish without having to sand it a lot. I don't know what it's called but I see a lot of peaks and valleys, I started with 320 and it will take a while to smooth it out.

    While spraying I can see the Duratec build up to orange peel which I wanted because I will need to sand, but when I go for a second pass in areas I think I am spraying too fast or something so the orange peel goes away and I think it will be harder to sand smooth.

    After I spray the Duratec to seal the mold plug, what grit sandpaper should I start with?

    What filler could I use to fill tiny scratches and pin holes without having to spray again?
     
  2. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    Here is the plug after spraying two coats of Duratec and with an upclose picture of where I sanded, can you give me some advice

     
  3. Scuff
    Joined: Nov 2016
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    Location: Richmond VA

    Scuff Senior Member

    Aaron it looks like pinholes in the second pic? If so, that may be contamination on the surface. What level of finish are you looking for? I sanded down to 1500 and then buffed with polishing compound. I found the duratec hard to spray but I'm not very good with the spray equipment.

    I tried to post a pic but it wouldn't load for some reason.
     
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    I don't see evidence of surface contamination.

    I do see lots of evidence of dry spraying. The paint is not flowing together and leaving pits between the globules.

    Are you flash coating?
    How long between passes?
    How long between coats?
    What is the wet film thickness of each pass and coat?

    I think your viscosity is too thick for your equipment.
    Try thinning.
    Start with a flash coat.
    Then slow way down on the secessive passes. The surface should be wet enough for the orange peel to flow together.
     
  5. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Use a 2.5 mm tip.

    Don't set the pressure too high (30 psi or so)

    Spray it heavy enough so it flows and levels easily. You don't want orange peel.

    Don't get too close so the the air pushes it around on the surface.

    The paper you start with is determined by how well you sprayed it. The smoother the spray job the finer the paper. But....

    If you're going to polish the primer and use it as a mold finish, you only need to sand to about 600 then buff.

    If you're going to spray a top coat over it, don't go finer than 120.

    If you need to thin it, use MEK or the Duratec thinner, you'll only need about 5%

    If you sand it the same day you spray it, it will sand easier, the longer you wait the harder it will be to sand. I'm not saying it will be difficult to sand later, just easier if you start sooner.
     
    Last edited: Jun 11, 2021
  6. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    Ideally what grit would you start sanding with after putting down the duratec?

    I had to start with 60 grit to really cut into all the roughness...I've actually rolled duratec and gelcoat with this type of finish before so I wasn't impress by the spraying. Good tips though I am using a 2.5mm tip but did not thin it. Yes I believe I am dry spraying because I felt the air was coming out without much duratec and actually changing the way the surface feels.

    Thanks for the help guys anything else you can think of?
     
  7. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    Good news this project does not need to have an end glossy finish so I can learn a little on spraying before I work on the next one that does need a glossy finish. Of course I want to get it as glossy as I can so it will pull form the mold but as long as its smooth the looks wont be as important and I guess I could always make the mold glossy in the future if needed
     

  8. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Less air and more Duratec will typically yield a smoother finish.
     
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