Epoxy + glass cloth protect Styrofoam underneath?

Discussion in 'Materials' started by Austin Reynolds, Dec 13, 2020.

  1. Austin Reynolds
    Joined: Dec 2020
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    Location: coastal BC

    Austin Reynolds Junior Member

    Hey there everyone hope life is treating you well. Currently I'm working on a small boat and the seats are styrofoam with 2 layers of glass cloth/epoxy laid over the styrofoam. I am working with Interlux 404/414 Epoxy Primekote which is recommending using a Thinner: "Interlux Brush: 2333N". The thinner contains a "slow evaporating solvent". Do you think it will seep through the 2 layers of fibreglass and melt the styrofoam if I use thinned primekote?
    Could you see a solution to the problem ie. more layers or do you know of a good marine primer which doesn't require a solvent thinner?
    Thank you in advance for your reply!
    -Austin
     
  2. ondarvr
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    ondarvr Senior Member

    As long as the glass is thoroughly wet out with epoxy it will be fine.

    Any pinholes or dry spots will let the thinner through though.
     
    missinginaction likes this.
  3. Austin Reynolds
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    Austin Reynolds Junior Member

    This is good news for me! But! I just noticed the paint contains xylene which will attack the styrofoam. Im in the market now for another primer//paint combo with no solvent or very little ideally.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Don't use a thinner ?
     
  5. missinginaction
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    missinginaction Senior Member

    He has to thin the primer Mr. E. The stuff comes out of the can(s) close to the consistency of yogurt. The Interlux Perfection can be used without thinning depending on the ambient air temperature but the finish coat contains isocyanates which I'd presume is going to attack a foam core. He should be OK though. A couple of coats of neat resin to seal up and get those seats smoothed down. Then two coats of cloth. If he's building up enough skin to support his weight that cloth will be maybe 9 oz.? Regardless, by the time he's ready to paint it I believe that it will be sealed up pretty good. Ondarvr's right though. He needs to be careful.

    Me? I'd just use plywood but I'm old school. Maybe he's using the foam core as double duty as flotation.

    MIA
     
  6. bajansailor
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    bajansailor Marine Surveyor

    I am a bit confused (this is easy to do for me) - Austin, are you building these seats yourself, or do they already exist in the boat, and you are just looking to paint them?
    If the latter, then I would have thought that the chances of any solvent getting through pinholes in 2 layers of cured fibreglass must be rather slight?
     
  7. ondarvr
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    ondarvr Senior Member

    If you have 2 good layers of glass on it, it makes no difference what solvents are in the paint.

    Again, this means there are no areas that are dry or with pinholes.
     
  8. Austin Reynolds
    Joined: Dec 2020
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    Location: coastal BC

    Austin Reynolds Junior Member

    Missinginaction, ondarvr, thank you both. Good information and helps bring me to the next phase of the build.

    I will try painting the glass covered styrofoam seats first with epoxy prime kote, thinned with brushing solvent, and see if it melts thru to the styrofoam/ I'll let people know how it went.

    Bajansailor, I built the seats and 'glassed them, then I read a similar build where a guy had used paint with xylene in it and it had melted chunks out of his foam, maybe his lamination was too thin.

    Thanks
     
  9. bajansailor
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    bajansailor Marine Surveyor

    Please do follow up with how the paint 'works out' on your seats - and if you have any photos of the boat, I am sure that we would all love to see these as well.
     
  10. ondarvr
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    ondarvr Senior Member

    There is no guessing, if you actually covered the EPS foam with epoxy you can apply any type of coating you want and it will have no effect on the foam.

    This is a common method of building plugs and shapes, there are polyester primers that can be used also.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd be more concerned that the essential strength may be lacking, light fibreglass cloth doesn't offer much. and styrofoam, next to none.
     
  12. ondarvr
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    ondarvr Senior Member

    Yes, two layers of light cloth probably wouldn't be strong enough to hold to much abuse.

    Heavier cloth or fabric may hold up OK.
     
  13. upchurchmr
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    upchurchmr Senior Member

    You need to look into building kayak seats with shaped "minicell" foam.
    No need for glass or any coatings and your posterior is well cushioned.
     
  14. Austin Reynolds
    Joined: Dec 2020
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    Austin Reynolds Junior Member

    There is a before and after. I have given two layers of epoxy primekote over styrofoam sheathed first in 2 layers 6oz glass cloth and epoxy.


    132167440_1277004149340284_1289333810456825381_o.jpg 132429026_1277004476006918_1058588443383041333_o.jpg
     

  15. Austin Reynolds
    Joined: Dec 2020
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    Location: coastal BC

    Austin Reynolds Junior Member

    Wanted to add how much this forum has helped me over time. I've been reading and studying here for a year now / the expertise of the gentlemen here has saved me hours and hours.
     
    missinginaction likes this.
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