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Thread: Epoxy not drying

  1. #1
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    Epoxy not drying

    I am having difficulty getting a clear epoxy to set up. The clear System Three is supposed to be quick setting,
    however my recent results is that it just does not set hard. It is rubbery after days.I am wanting to fill small
    splits in mesquite wood.

    I have a little better luck with Loctite white marine epoxy, but after hours it is still a bit rubbery.

    What can you say about your experience with epoxies.

  2. #2
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    Lowell,

    A couple of thoughts.

    First, is the epoxy fairly recent stock, or old stock? If it is old stock, it may not co-polymerize as thoroughly as desired, which could give a result like you are seeing.

    The other possibility that occurs to me is a failure to mix it thoroughly. I like to stir the material well for about a minute, or more. You need to get the two halves extremely well mixed so that the two materials are in intimate contact at the molecular level. This greatly helps with the polymerization bonding. This extensive mixing is especially important if the epoxy is a little older.

    Just my two bits.

    Stew

  3. #3
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    I am having difficulty getting a clear epoxy to set up.
    This happened to me recently.

    I attributed it to the shop being cold. Checking the weather indicates that isn't the likely problem.

    My epoxy is old, the mixing may not have been as thorough as needed.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  4. #4
    How are you measuring the parts? I've used a lot of T88, which is slow setting. I use a scale to measure out the 1:1 ratio. Mix well.

  5. #5
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    I agree with the above comments. In summary, the most common causes of improper curing are:
    • Improper mix ratio- epoxies are very sensitive to mix ratio. Use calibrated pumps or a scale. Double check the mix ratio, as it differs by brand.
    • Low ambient air temperature- typically this only causes a slower cure, but if it is really cold it can cause it not to cure at all.
    • Old or bad epoxy- If it is old, usually the hardener will turn yellow to brown or even purple. It may also have gotten moisture in the epoxy. This can sometimes cause discoloration, but sometimes it looks fine but won't cure. It will usually foam up when you spread it out in the cloth if it has a lot of moisture in it, but in pours like you're doing it won't be as obvious. Epoxy that has been allowed to freeze during winter or get really hot in summer may also go bad and not cure. Freezing may not change the color. Overheating usually will darken the hardener. Freezing is worse for epoxy than getting too hot.


    One thing to note when filling large gaps- it is best to add some wood flour or colloidal silica. Epoxy needs a fill agent for strength. This, however, is not why it's not curing. It should still turn hard without a fill agent. I am just mentioning for when you do get the cure issue solved. For gaps 1/4" or larger you want to use a thickening agent. Microballoons (also known as sanding filler) will make a more easily sanded product. It will turn the epoxy a chocolate to reddish-brown color. Colloidal silica will turn white to gray. It's very hard to sand and tough on cutting tools. Wood flour (fine powdery sawdust) will turn much darker when mixed with epoxy and makes a strong and sandable fill. Pine flour turns mahogany color. Teak turns black. Test a small batch before using to see what color you get. You can also tint epoxy black with copier toner if you want black. Just some ideas on the topic for your consideration.

  6. #6
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    Thanks guys. I appreciate it. I will use wood flower in the splits. I'm glad I posted here because I didn't know pine turns dark brown and that is the color I need.

  7. #7
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    Most problems with epoxy stem from insufficient mixing. You need the proper ratio of resin to hardener, and you need to mix very well. I usually mix until it looks completely clear and even, and then mix that long again. I've never had any epoxy fail to harden, and I've used gallons of system three epoxy, including some that was over a decade old. At low temperature it will cure slowly.

    The one thing to watch out for on storage, particularly if it's cold, is crystallization. If you see solid in the resin, gently warm until it melts and mix it in before use. Otherwise, that part of the resin will not mix properly with hardener, and you will wind up with at least regions having the wrong ratio.

    The ratio is important: you can think of the resin as mortised and the hardener as tenoned. The strongest structure will result from mixtures where each mortise and each tenon has a partner.

    It is true that with the right filler, epoxy can be stronger. But in my mind the main advantages of fillers are economy and appearance.

  8. #8
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    Epoxy that has been allowed to freeze during winter or get really hot in summer may also go bad and not cure.
    This could be another of my problems since my shop isn't heated in the winter.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  9. #9
    I use S3T88. My experience mirrors others: mix well and beware if it's old. That being said, it has always eventually hardened up for me. Just may take a couple days. I've never had it stay soft forever.

    I am never that scientific in how much I mix together. I try to do it by sight if it's less than an oz sized batch. I mix that for about 30 seconds, until it's a pherfectly phlegmy yellow with no swirls.

  10. #10
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    My epoxy has cured by today. It cures with a sheen, but after I level the cured epoxy with a chisel, it has the proper appearance.

  11. #11
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    Quote Originally Posted by lowell holmes View Post
    My epoxy has cured by today. It cures with a sheen, but after I level the cured epoxy with a chisel, it has the proper appearance.
    I checked my last epoxy job today and it is hard.

    My dad showed me about making scotch tape dams for epoxy or to put it over where a gloss finish is desired. Gosh, that had to be about 50 years ago. He also taught me not to toss any left over epoxy so it could be checked for hardness instead of checking where it was applied.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  12. #12
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    Quote Originally Posted by Jim Koepke View Post
    I checked my last epoxy job today and it is hard.

    My dad showed me about making scotch tape dams for epoxy or to put it over where a gloss finish is desired. Gosh, that had to be about 50 years ago. He also taught me not to toss any left over epoxy so it could be checked for hardness instead of checking where it was applied.

    jtk
    That is a good tip, thanks.

  13. #13
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    I mix my epoxy in a little plastic throw away cup, so that I always have a check on the hardness. They are little ketchup cups.

  14. #14
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    Well,
    Yesterday, I decided I wanted some clear 5 minute epoxy. I ordered some from Amazon.

    It is 2:28 PM and the postman put it in my mail box 15 minutes ago. That is SERVICE , I don't know how they do it.

    I thought I might share this with you.

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