Epoxy over laminating polyester.

Discussion in 'Materials' started by Canracer, Sep 3, 2016.

  1. ondarvr
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    ondarvr Senior Member

    I watched them, That's why I made the comments.
     
  2. Canracer
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    Canracer Senior Member

    Ok, so your question is "what are you doing." Firstly, I'm just having a little fun with this kayak. It was somewhat well used and eventually the "legs" of the cockpit seat started to poke through the bottom of the hull. I took on water one day while out fishing.

    I considered the repair, and imagined a plastic kayak with fiberglass inner reinforcement. The idea seemed unique enough to be an entertaining challenge. I laid down the glass, it released easily from the hull, and I then re-adhered the panel with West System G-Flex.

    I might have spread the G-Flex a little thin; part of the learning process. But the panel is in place. The plan now is to reinstall the seat and then go boating. The forces introduced into the hull through the seat legs should now be well distributed.

    The same technique could be used to install frames and bulkheads. The goal being to breath new life into a polypropylene kayak.
     
  3. ondarvr
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    ondarvr Senior Member

    I understand all that, your question was about bonding epoxy to polyester, that part of the project isn't clear.
     
  4. Canracer
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    Canracer Senior Member

    I'm considering adding more to the panel. Maybe a few small frames or some coring. something to increase stiffness. I have a bunch of new epoxy and my polyester stash is really old. So I'd like to continue with epoxy.
     
  5. ondarvr
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    ondarvr Senior Member

    Clean it with acetone to remove as much of the sticky resin as you can, then sand it and clean it again with acetone.
     
  6. Canracer
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    Canracer Senior Member

    This makes a lot of sense ondarvr. Unfortunately I didn't see this post earlier and I drove down to West Marine for a bottle of PVA. It might get returned.

    I tried the solvent wash approach with alcohol and it does work to a degree. Next I'll add some sanding. (I have some acetone too, will give it a try.)
     

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  7. mydauphin
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    mydauphin Senior Member

    I have used the hot resin method dozens of times, including once in a situation of a freak storm getting everything wet. If you make it too hot yes it gets more brittle but remember I said add then sand it down. All resin will cure over time, you just need to get reaction started. Putting it out in the sun, or heat room afterward will also help. In the case of epoxy, if you screw it up, it will never cure.
     
  8. ondarvr
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    ondarvr Senior Member

    If you're sanding it completely off it doesn't make a difference if you mess up the mix, but if you plan to leave it on there it makes a huge difference.

    Polyesters don't eventually cure over time, they need the correct amount of catalyst to crosslink completely, although it may eventually get hard being heated or placed in the sun, this is not the same thing as curing correctly. Physical properties can be reduced significantly by over or under catalyzing.
     
  9. mydauphin
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    mydauphin Senior Member

    Everything you are saying is true, but these are not spaceships or structural parts like stringers. It is a canoe, it is a mistake and it is easy to fix and go on. If it was a hull then more proper controls are needed to start with.
     
  10. Canracer
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    Canracer Senior Member

    This kayak sat in my very hot Florida garage for a year. It is still very sticky. If left out in the sun, the UV radiation might decrease stickiness, but it would also breakdown the resin the was properly cured.
     
  11. ondarvr
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    ondarvr Senior Member

    Short term the UV rays won't do any damage, so that isn't a concern. The problem is epoxy and polyester chemistry aren't compatible in the uncured state, so you need the sticky surface to be fully cured and/or sanded off for the epoxy to bond well. If the entire laminate is still soft (probably isn't) then it would need to be removed completely.

    Acetone should remove the sticky surface, then a light sanding should work fine.
     

  12. ondarvr
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    ondarvr Senior Member

    My view is that whether it's a critical component or not, using the correct methods ensures you'll get the best results possible. In this case if he does it incorrectly the epoxy may not cure, and if it does, it may come loose easily, not a good result. Applying more polyester resin at the correct ratio and prepping the surface, or removing the sticky surface currently there will give the epoxy a good surface to bond to.
     
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