How to fix slow-curing fiberglass resin: MEKP diluted with?

Discussion in 'Materials' started by kayakingsteve, Aug 27, 2021.

  1. kapnD
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    kapnD Senior Member

    CSM can conform to some crazy curvatures because it’s strands are not woven or oriented in any particular direction.
    A dabbing technique with a wet brush will lay it down, rolling may not be possible in some situations.
    It can be torn into smaller pieces laid overlapping to avoid big wrinkles, and the torn edges become invisible, leaving no edge lump.
    Dabbing with the bristles works pretty well to lay down woven reinforcement too, but you need some experience to know the limits of your materials, and where to place strategic slices.
    I have used the trash bag technique in bowl shaped lamination situations, filling it with water to flatten it out, much like using a vacuum bag, which is your ultimate answer. Take great care to not contaminate the laminate with water!
    As for your original question re spotty cure, make certain you mix well, but quickly, and in Florida, do NOT leave it in the container, start work immediately. In fact, I have sometimes refrigerated my resin prior to mixing to help extend working time in. After mixing, you can pour into a wide shallow container to slow down heating , or bulk it on the work surface quickly, then get back to the detail work.
    Your hardware store resin probably does have some wax in it, sanding after cure will tell for sure. Unwaxed lam resin gums up sandpaper quickly!
    ondarvr likes this.
  2. kayakingsteve
    Joined: Aug 2021
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    kayakingsteve Junior Member

    ***Solved: turns out crappy Bondo fiberglass resin was the issue the whole time. No ingredients on the can, no specification of what type it was, not using it again. Bought some marine finishing resin and it works exactly the way you fellas say it should.

    Got dry enough to sand, then used some proper marine finishing resin with another patch and by contrast, that cured within an hour. I used the resin in a shallow container and worked small, like you said. Was perfect.

    Will have to start experimenting with some fiberglass techniques so I'll be ready next time to work on a boat.

    Will overlapping small pieces give you the same structural strength as larger pieces once resin cures?
  3. kapnD
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    kapnD Senior Member

    Overlapping reinforcement within a lamination is very necessary, and actually adds strength in overlap areas, which will ideally occur at keel, chines, and transom corners.
    Overlapping of Matt doesn’t add much structural value, but adds to resin weight/volume.
    I suggested that previously as a means to make it behave in curvy circumstances.
  4. kayakingsteve
    Joined: Aug 2021
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    kayakingsteve Junior Member

    Thanks for the info; it's a lot to process, but I'm learning, slowly!

    Do you get bitten by the "fiberglass bug"? I was dreading working with this stuff, but now I'm actually wanting to learn how to do it well and maybe build some things.
  5. kapnD
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    kapnD Senior Member

    The fiberglass bug will bite you, as soon as you get to a point where grinding and sanding become a necessity.
    After a bit of that, you may not be so enchanted!
    I will agree that GRP is a fascinating medium to work with, but the nasty fumes and inevitable itch that come with it are a major deterrent.
    Re the spotty cure, always shake/mix the resin before pouring out of its container, components tend to separate during storage.
  6. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Look at the date of manufacture of the bonds.

    Diy stores don't sell enough resin. It can sit on the shelf for years. Spoiling. It ought to be used within six months of manufacture.

    It will eventually fully cure. It's just a drag to use.
  7. Tops
    Joined: Aug 2021
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    Tops Senior Member


    I do not think Bondo resin is waxed from the factory. So it will be air-inhibited, staying slightly tacky on the surface to accept the next layer.
    The polyester resins are also pre-promoted which means they are already in a state of curing which is very very slow until the MEKP accelerator is added. If it pours out of the can it should be OK. I did have one can of resin fail but I cannot remember if it was Bondo or something more 'professional' (I used both) but that was straight up gelled in the can. We just used an old (at least 2 years) can of Bondo resin this summer for boat (fillers added) and car bodywork (cloth and pigment) and it did fine and was sand-able next day (I normally wait overnight, habit from epoxy).

    My biggest mess with waxed polyester resin was a gloss coat on a surfboard. Working in lower temps (65 F / 18 C) and I overworked the surface with the brush, disturbing the wax layer. It was all very sticky next day. Tried the wax paper/wait a few days trick which helped a little. I don't quite remember the rest, thinking I may have sanded/wiped off the rest of the wax and had a do-over. The takeaway was warmer temps and brush it on quick: long way, short way, long way, then walk away....
  8. Scuff
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    Scuff Senior Member

    Pics of the surf-ski if you have any
  9. member74761
    Joined: Aug 2021
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    member74761 Junior Member

    I do things a LOT different than most.
    I experiment with all my epoxies & resins, Before I start a project or think I going to put it on my boat,. and at this point I have already done that.(micro batches)Test their strength, and then with additives like cabisil or fumed silica, then milled fibers or sawdust or chopped strands. then bonding resins over epoxy, that is a no no, but giving weeks to cure before layover. This is time consuming and tedious, and a little product waste.
    But if I'm glueing stringers, I want to know its there and going to hold. not oh I hope this works out.
    I have different epoxies that have night and day different working times, some 1/2 hour others 4-6 hours if you pan it or keep it thin layered out of the sun, with 8-10 hrs tacky. again knowing your products and what to expect. is key and you will get a confidence level quicker.
    This stuff is Not hard to work with after you learn its quirks and how it likes or doesn't like to be applied.
    Most times these 2 are forgiving and simply sand and re-do til you get it how you like.
    (But practice on something before you screw up a nice piece)
    You can learn this... we all did at some point.
    All the guys that got this right the 1st. time,. well we won't count them. they had good teachers.
    I learned all mine trial and error. But I am very secure and at home with whatever I need to do....... NOW.
    And I have cheap epoxy for filling and top shelf for structure. but again know what and where and how for different products and why. I have found several different levels and pick and choose where and how they will serve me and their purpose.
    They all have their place.
    Best of luck.

  10. gonzo
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    gonzo Senior Member

    Bondo resin is waxed. What is generally called "yard resin" or "all purpose" is marketed for quick small repairs and not for laminating several layers.
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