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  1. #1
    AeroncaChamp is offline Cast Iron
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    Default OT: getting old fiberglass resin to harden?

    I think I screwed up - used an old (15y.o.?) fiberglass kit for a patch job ... resin isn't hardening. It had been opened and partially used when new, then stored away for a future need...

    I mixed as per directions - I suspect either the resin or the hardener has lost that special something that makes the mixture harden.

    Does anyone know any tricks to get it to harden? Is the next step to scrape the gooey mess off, strip it, and start over?

  2. #2
    Milacron's Avatar
    Milacron is online now Diamond
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    Default

    Would help to know just how large the patch area was. If not more than a few sq inches I would remove it with MEK (Methyl Ethyl Keytone) and start over.

  3. #3
    SteveF is online now Stainless
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    How long ago did you use it? I had some once that took several days to fully harden.

    Steve.

  4. #4
    SlicerMan is offline Hot Rolled
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    Prolonged heat maybe.
    Not real hot. 150F .
    It's a long shot.
    I would start scraping.
    SM

  5. #5
    mfisher is offline Cast Iron
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    Default What type of epoxy?

    Is it the polyester resin (just a few drops of peroxide catalyst and mostly the resin) or the 'West Systems' or similar 201/202 5:1 type epoxy?

    If it is one of the former, it could be the MEK peroxide catalyst has gone bad. If you need to get a new batch of epoxy anyway, you could just try wiping the surface of the patch with some of the new hardener, and be patient.

    If it is a simple patch, that can be easily redone, probably best to just get all the old out and start over.

  6. #6
    Weirsdale George is offline Stainless
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    As recommended by Mfisher, I, too, have gotten out of this bind by painting the uncured surface with a small brush dipped new hardener. (Were it a critical application like below the waterline on a boat, I would definitely recommend digging out the old and start over.)

  7. #7
    gnorbury is offline Hot Rolled
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    Clean off the uncured goo and start again with fresh materials. Chances are the old stuff will not have any strength even if it does finally go hard.

  8. #8
    Sea Farmer is offline Titanium
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    I agree with Slicerman.

    Start scraping

  9. #9
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    dpasek is offline Aluminum
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    One thing that hasn't been mentioned is that you do not want to mix systems. Peroxide cure polyester resin that contains styrene monomer will not cure properly if applied over epoxy resins. The free amines that remain after epoxy cure will inhibit the free-radical cure mechanism of the polyester.

    If you are using polyester resin only, and not epoxy, the most likely problem is bad catalyst. The MEKP in 'liquid hardener' has most likely deteriorated after 15 years.

    Regards,
    Dennis

  10. #10
    bob ward is online now Aluminum
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    Default 15 years old???

    Polyester and epoxy resin systems both have a shelf life, but neither of them are anywhere near 15 years.

    Polyester has a max shelf life of 6 to 12 months from date of manufacture and the MEKP hardener 12 to 24 months. Sometimes you can use up old resin by using increased amounts of fresh MEKP, but even if you can get the resin to set it will be understrength, so don't use it for anything important. Polyester resins are the ones with a 100:1 or thereabouts resin:catalyst ratio.

    Epoxy resins have a much better shelf life than polyesters but 5 years would be pushing it. Epoxies are typically the systems with mixing ratios of from 1:1 to 5:1

    Both systems basically just lose their reactivity over time.

    If you are talking about a kit I guess we are talking fairly small quantities, so its best as others have said to buy fresh materials and start again. Scrape off what you have done and clean up with acetone for a polyester system and MEK (that's MEK not MEKP) for an epoxy system.

    Take some clean empty glass jars to your local fibreglasser and get him or her to fill them for you, he or she will be using fresh materials.

    Avoid the prepacked kits from the big box stores, they could have several months on them before you buy them and may have been made with old resin anyway. The big box stores put severe price pressure on the guys that make up the kits just like they do to every other supplier.

    To maintain margins, the kit makers will buy the cheapest resin they can, which is quite often the out of date drum that has been forgotten in the corner at the resin factory. Or maybe it is the drum returned by the fibreglasser because there were problems with the resin. As long as the resin is still liquid and can be poured into their little kit tins, what the hey!

  11. #11
    AeroncaChamp is offline Cast Iron
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    Thanks all

    It is/was the resin/MEKP type stuff. It's only ~1 sq ft or so, so I'll be scraping and cleaning up the old goo. Too much and maybe a little thick to re-treat with fresh hardener and the extra strength I'd get from a fresh batch wouldn't hurt either.

    Shoulda listened to that little voice in my head - the one that said "i dunno, this stuff is older than your teenager" not the one that said "wow... it's still liquid and it smells like fiberglass resin". Now to find that local guy that might sell me a jar or two of fresh materials.

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