post curing epoxy

Discussion in 'Fiberglass and Composite Boat Building' started by bladerunner, Dec 29, 2014.

  1. bladerunner
    Joined: Dec 2014
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    bladerunner New Member

    I was thinking of using a propane construction heater ( sort of like a tube with a blower with 350 K BTU and tarping off the hull. Has anyone tried this and if so what kind of temperatures could you achieve?
     
  2. Mikeemc
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    Location: South Carolina

    Mikeemc Junior Member

    In my past experience heat speed curing epoxy that is 2part mix damages the molecular structure of the resin. Use it at the manufactures recommended temperature and set time. If your new to epoxy do small batches, 2 cup mix procedure, and always keep a log on daily temperature and size of batch mix. Go through a dry run on your layup and time it just like you would if you were laying the resin on and add 2to 3 minutes per yard ( flat surface ) , curves and crannies take longer to wet out and dress right. Remember No Wax on first coats. Hope that gets you going.

    If you know Chris Hanson he's a good guy to get to know , if Frank is still at Delta boat in the port talk to him. Spent my mislead youth in that place, lol just kidding
     
  3. PAR
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    PAR Yacht Designer/Builder

    This is incorrect Mike, most experienced builders post cure, even room temperature cure formulations, if only to get it hard faster and prevent fabric print through. The molecular bonds will take place, no matter what, assuming it's warm enough to do so and with room temperature cure goo's, this is anything above near freezing. Slow and very slow hardener formulations may need higher temperatures, say 70 degrees, but it's going to cure, like it or not.

    I wouldn't use a kerosene or propane heater for this process. Most shops have way too much dust floating around for this to be a wise idea. Most importantly, you can't control temperature. I use oil filled electric heaters, which have thermostatic controls. I can put them under a tarp without worry, open flame just is asking for a problem. You can half the cure rate of room temperature cure epoxy at 110 degrees, which is what I shoot for. Once you get into the 130 degree range, it'll cure quick as hell, but you're also pushing the edge of the goo sagging or distorting from the heat. This is why it's important to have temperature control. Keep it below 120 and you'll be fine.

    I'm not sure what you mean by wax Mike, but this discussion is about epoxy, not polyester.
     
  4. Mikeemc
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    Mikeemc Junior Member

    Ok I stand corrected , I must have something wrong , it's been about 25years since I've worked with it on boats. My home deck is fairing well after 22 years , epoxy , and yes I use wax on final finishes always have.
     
  5. PAR
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    PAR Yacht Designer/Builder

    What type of wax are you using on epoxy? Is this a finish or a release agent?
     
  6. Mikeemc
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    Mikeemc Junior Member

    I still have the can at the house , this weekend i'll take a look. I purchased it from the old FRP out of Tampa back n 1992 when I did the deck on the house. When was in Ft Lauderdale mostly did polyester, some epoxy. Yes it was a finish wax , additive. Before when I didn't use it the epoxy would just gum up the sand paper or grinding disks. Want some real vintage epoxy resin lol. I also use UV additive and use high solids black as primer base for extra UV protection.
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    The point about fire security with the dust is very real also. Par is right. I would never use that in a shop filled with flammable stuff...I do see also a very big drawback in using propane heaters for curing epoxy; propane combustion releases a lot of carbon dioxide, carbon monoxide, and lots of water vapor. It's the the best way to have the epoxy milky, filled with water (the hardeners are very hydrophilic when not totally cured) and plenty of wax-like carbamate on the surfaces, making posterior sanding an horror. It's also a risk of asphyxia. I won't talk about condensation and the water running from the tarp.

    Like Par I've always used oil filled electric radiators and spark proof ventilators for equalizing the temperatures. They have the advantage of being very safe, very sturdy and it last years and years. Like Par I've used a lot of slow curing epoxy, post cured at 120 F ( around 50 C), It's an excellent method. 120F is very easy to attain, and the relative humidity goes very low, so the cured epoxy has no flush. The problems of deformation are around 60C and above with ordinary resins.
     
  8. gonzo
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    gonzo Senior Member

    High temperature can also be used to temper a polymer. Check online, there is a fair amount of literature on the subject.
     
  9. SukiSolo
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    SukiSolo Senior Member

    I agree with using 'dry' heat and prefer oil filled electric rads too. Propane is a nightmare for moisture and causes bloom on cellulose paints etc etc 'nuff said.
     
  10. pauloman
    Joined: Jun 2010
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    pauloman Epoxy Vendor

    FYI - epoxy cure is a simple chemical reaction. It doubles or halves with every 18 degree (10 C) temp change - as do all chemical reactions

    paul oman
    progressive epoxy polymers inc
    epoxyproducts.com
     
  11. bladerunner
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    bladerunner New Member

    I have an aerospace prepreg that requires a 300 degree F cure cycle.
     
  12. upchurchmr
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    upchurchmr Senior Member

    Are you going to use the 80PSI pressure on the laminate that is typical of an aerospace composite?

    It would have been nice if you mentioned that to start with to avoid useless discussion.
     
  13. SukiSolo
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    SukiSolo Senior Member

    Could be fun watching the 'tarp' at that temperature.....;)
     
  14. TeddyDiver
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    TeddyDiver Gollywobbler

    Also remember to rise the temperature very slowly. Like first hour to 100F next hours 10F increases per hour. Once you reach 140F (absolute max) keep it there for 6 hours, if it's "colder " double the time for every 10F below 140F.
    BR Teddy
     

  15. upchurchmr
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    upchurchmr Senior Member

    A typical cure cycle for aerospace graphite/ epoxy has a faster heat up rate and much higher temp.
    I believe bladerunner said his was a 300F cure epoxy - why would he heat only to 140?

    If it would really be useful I can get the heat up rate, but I think it is around 80 degrees / hour.
    The real concern is that he doesn't have the curing pressure probably required to get a good laminate, unless he has another surprise for us.
    Second concern is being able to get a consistent heating of the whole structure at the same time.
    Cooldown also needs to be controlled.
     
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