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Thread: What epoxy to use?

  1. #1
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    Default What epoxy to use?

    Hello! I need to glue 2 pieces of marine plywood 3/4 toghether. What epoxy or glue would you suggest?


    Thanks,

    Alex-

  2. #2
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    Default Re: What epoxy to use?

    Uuuuuhhhhh...what are they going to become? Might make a difference in what you use. My preference of late has been epoxies with unthickened applied to both sides, then an even coat of thickened applied. That leaves a visible line, however, so whatcha doin?

  3. #3
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    Default Re: What epoxy to use?

    Tell us more...
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  4. #4
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    Default Re: What epoxy to use?

    Im remplacing the transom, which was 2 x 3/4 glue toghether. You can still see the glue under the rot.

  5. #5
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    Default Re: What epoxy to use?

    Do not use a 5 minute epoxy.

    Any of the major brands will do the job, and if you can find a significant difference, you are a better judge of adhesives than anyone I have ever met.

    This is an old epoxy comparison test that is worth reading. It is the only one that I can find that compares so many and explains so much. http://www.oneoceankayaks.com/Epoxtest.htm The test was done a long time ago and there are more good epoxies available now.

    If you are used to using any of the common brands, I would stick with the epoxy that you are familiar with.

    {Edit after posts 6-9: I agree that blush is not an issue for this application and should have added that. I brought up blush because the OP and others looking at this may well have other uses for the epoxy where blush will be a consideration.} Most people here are used to West System and will recommend it over any other and defend it to the death. West is a good material, but it is prone to blushing. If you are starting from scratch, a non-blushing epoxy is preferable. Blush is formed by the hardener when the epoxy is cured in cool high humidity conditions. SOme epoxies blush a lot more than others and some people, who must have running water in their shops, feel that washing the blush off isn't inconvenient at all. Because any epoxy might blush under the worst conditions for curing epoxy, they argue that you should always wash and scrub all epoxies every time. That isn't exactly correct. Blush is not a problem if you apply more epoxy over partially cured epoxy before the blush develops.

    There are some oily hardwoods that can be more difficult to glue. Plywood is not one of them. For oily hardwoods the particular epoxy and surface preparation do make a difference. West G-Flex and System 3 G-2 are good for oily hardwood.
    Last edited by MN Dave; 09-13-2018 at 12:54 PM.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  6. #6
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    Default Re: What epoxy to use?

    Yes to everything MN Dave posted.

    And, under my rock, my little hillbilly tests demonstrated that surface prep, of the non-blushing poxy that I use (West 105/207) in my environ, is not necessary. No washing, no sanding, and the secondary (mechanical) poxy bond was stronger than the plywood.


    My hillbilly tests are described at https://boatladyc.blogspot.com/2018/04/bond-rating.html

  7. #7
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    Default Re: What epoxy to use?

    "Blush" happens when moisture in the air draws hardener out of an exposed coating of uncured mixed epoxy. The hardeners are water soluble.
    If bonding two panels together, as the OP is doing, there is no exposed epoxy, except for squeeze-out, and hence blush isn't an issue.

    According to the Gougeon Brothers book , the amount of epoxy needed for an interlaminate glue joint is about 1 lb. per 13 ft^2.

    If he subsequently elects to sheathe his transom with glass, and covers the wet layup with peelply while it cures, any blush will form on top of the peelply and comes off with the peelply.
    He'll get a smoother finish, too.
    Last edited by JimConlin; 09-12-2018 at 10:54 PM.

  8. #8
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    Default Re: What epoxy to use?

    What all of those guys said, plus make sure you seal ALL exposed end grain on the ply. I'm assuming this is a flat transom? If it's curved and you're having to form the ply over a form take care not to starve the joint at the point of highest pressure. Some diagonally scored lines on the facing plies will help...like maybe drag a sharp saw across the surface to provide some "tooth", but try not to penetrate the outer ply.

  9. #9
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    Default Re: What epoxy to use?

    As Jim said, blush (or not) has no bearing whatsoever in this particular application. My method for similar projects (including once replacing the entire bottom of a Simmons Sea Skiff using two layers of Bruynzeel plywood) Is to roll a thin, even coat of plain epoxy/hardener mixture on both surfaces and let it soak in for a few minutes. During that few minutes I mix some microfibers (sold by the epoxy vendors) into the remaining resin to thicken it up a bit and increase its gap-filling ability. I next spread a thin coat of the filled resin on one of the surfaces and proceed to stick them together under moderate (but not extreme) pressure. Clamps, weights, staples, nails or whatever works can be used to create pressure. You should have enough to get some squeeze-out, but excessive pressure will actually squeeze out too much resin from the joint and weaken the bond.

  10. #10
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    Default Re: What epoxy to use?

    Quote Originally Posted by Notmattdamon View Post
    Hello! I need to glue 2 pieces of marine plywood 3/4 toghether. What epoxy or glue would you suggest?


    Thanks,

    Alex-
    Lots of good advice, but no obvious answer to your question, so I will go ahead and say that you need to use a two part marine epoxy, and that is what everyone is referring to. Typical brands are West Systems, MAS, RAKA, System Three, TotalBoat, et al.

    As mentioned, you do not want to use "5 minute" style epoxies or anything similar that are available at the typical hardware store. Marine chandleries in coastal towns will have marine epoxies, as will West Marine stores in larger US cities, and there are many online dealers. I recommend DuckworksBBS.com

    Thickening agents should be added to already mixed epoxy to make it into a more effective adhesive. As Todd says, microfibres are perhaps best for this, and can be found at the same dealers.
    You will need to do some reading about epoxy and thickeners, but it's not difficult. The most important issues with epoxy are getting the ratios between resin and hardener correct, and that they are mixed very thoroughly. Two minutes of mixing for a cupful is just a minimum.

    Read the instructions, wear nitrile gloves, eye protection and at least work in a well ventilated area.

    Good luck!
    Dave
    Last edited by DGentry; 09-13-2018 at 11:43 PM.

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