New to polyester resin

Discussion in 'Fiberglass and Composite Boat Building' started by Bigtalljv, Nov 28, 2022.

  1. Bigtalljv
    Joined: Aug 2019
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    Location: California

    Bigtalljv Junior Member

    Hi,

    Ive only used epoxy in my boat work prior to now but due to the future quantities needed I am exploring using polyester to laminate large surfaces like bulkheads, cabin walls, and such. Now I have dug myself a hole in that I have epoxy covering most of the hull so I’ll need to tab and join parts with epoxy but that should be ok.

    my local supplier has polyester laminating resin. My understanding is that while it’s super handy for doing multiple layers and offers longer times between layers the last layer or top surface needs to be “cured” before bonding with or to epoxy.

    the most common way to cure, it seems, is to add wax to the resin. I DO NOT want wax anywhere near my work area. So the other common but maybe less common is to spray the top with PVA. It’s water soluble so it should wash off better and hopefully be less dangerous than wax to future bonding.

    Do any of you use PVA for the surface cure? Do I need an HPLV type spray gun or can I use a spray bottle or something less high tech? (I have compressed air and an HPLV gun but it’s a lot for small parts).

    I know it’s maybe a little crazy but polyester is 1/3 the price and I don’t want to burn money if I don’t need to, there will be plenty to spend it on….

    thanks
    Jason
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    First, you should try a small area test to make sure the polyester cures over the epoxy. There are some epoxy formulations that affect the cure. If you don't want to wax the polyester resin (it only needs it for the last layer) there are easier ways to make it cure. Spraying PVA is messy and a hard job to clean well. You can use polyethylene sheets over the laminate to keep the air out. After you lay the fiberglass, you simply put the plastic over it and squeeze the air out. It will also give you a smoother surface finish.
     
  3. Bigtalljv
    Joined: Aug 2019
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    Bigtalljv Junior Member

    Thanks. Plastic sheeting does sound easier. I hadn’t seen that option discussed. Hmm I could even vacuum it a little….

    I am not putting polyester over epoxy. I am planning on building polyester laminated panels and then using epoxy to tab them into place. Epoxy over polyester.
     
  4. gonzo
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    gonzo Senior Member

    That will work with no problem. I have used polyester and vinylester over polyester with success. I got lucky they were compatible. Tests show that some epoxies won't let polyester cure.
     
  5. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    99.999 % of all polyester laminating is done without using anything to enhance the surface cure. It will cure sufficiently on its own after a short period of time.
     
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  6. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Be aware that compared to epoxy, polyester resin has a much shorter pot life.
    I’d definitely keep a spray bottle of PVA on hand for the last layer, you probably won’t have time to mess around with plastic sheeting or vacuum on large or complicated parts.
     
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  7. gonzo
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    gonzo Senior Member

    Can you post any data backing that? I have used all types of resins, and the open time for polyester is long enough to build 70 ft boats. I can't see how it is too short for small tabbings.
     
  8. redreuben
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    redreuben redreuben

    Use peel ply.
     
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  9. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Senior Member

    Standard MACT compliant / low HAP resin will be blended with DCPD to reduce viscosity without added styrene. It will cure tack free within 1 day. Your chemical bonding window is a maximum window of 72 hours.

    for epoxy tabbing, it’s less of a concern. Grind, wipe clean, tab in with epoxy.
     
  10. Bigtalljv
    Joined: Aug 2019
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    Bigtalljv Junior Member

    Well it was easy enough to throw some plastic sheeting over it, seal with masking tape to my steel welding table, and vacuum it down, it came out great, nothing tacky.

    If I use peel ply on the polyester do I need to sand before I use epoxy to tab it in?
     
  11. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    The texture left behind by peal-ed-ply is usually suitable for the next layer of laminating.
     
  12. redreuben
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    redreuben redreuben

    Depends; if it’s a structural joint like a bulkhead I like to expose fibre to the new resin. If it’s just a shelf then no.
     
  13. Bigtalljv
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    Bigtalljv Junior Member

    That’s a good point….
     
  14. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    I've seen test data that indicates an untouched peelply bond is better than a sanded peelply bond. It was a while back and I can't remember which peelply was used, there are different types.
     

  15. Bigtalljv
    Joined: Aug 2019
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    Location: California

    Bigtalljv Junior Member

    That’s a good point….

    ahhhhhhhh! So probably no matter what I do it’s probably not going to fall apart.
     
    redreuben likes this.
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