wrinkled fiberglass!

Discussion in 'Fiberglass and Composite Boat Building' started by mudflap, May 30, 2023.

  1. mudflap
    Joined: Jun 2020
    Posts: 10
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    Location: texas

    mudflap Junior Member

    Hi all-

    I purchased some 4oz fiberglass cloth online from a company I've bought from (with good results) in the past.

    Unfortunately, this batch of cloth arrived wrinkled:


    I thought/hoped that I could flatten out the wrinkles when I applied the bond coat of (Raka) resin.

    No luck. Whether I used a roller or squegee, the wrinkles would disappear for an instant, and then they would come back.


    (photo taken after one bond coat + one fill/top coat)


    I've gone at this with an elec orbital sander with 80 grit and knocked off most of the high spots, stopping when I can see that I'm close to sanding into the fiberglass cloth.

    There are no signs of air pockets under the wrinkles.

    Plan is to apply another fill coat and sand again. Probably will repeat again after that.

    Best guess is that I'll have things pretty well leveled out at that point. Considering topping with a textured truck bed liner which will go a long way towards hiding any imperfections in the finish.

    Any big concerns about this compromised application of fiberglass? Not really worried about losing any strength (underlying structure is pretty stout), but wondering if this will increase chances of delamination?

    Thanks for any help. Only those who are thinking "this won't be a problem" should reply. haha
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    If it was aerospace and carbon it would matter. Cloth over plywood is mostly a cosmetic thing that you'll learn to live with. Don't sand through the high spots, that may cause a problem.
    Last edited: May 30, 2023
  3. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    The only way to get rid of those fabric pulls is under vacuum or to pull it out of spec.

    If you sand thru, overcoat the feathers with epoxy. Carry on...
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    My Google search came up with 3 mentions of using denatured alcohol to smooth the creases.
    Maybe its the "size" on the glass that is holding the wrinkles.
  5. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Looks like a manufacturing flaw. I can’t imagine how it got to the marketplace, but you should be entitled to a refund.
  6. comfisherman
    Joined: Apr 2009
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    Location: Alaska

    comfisherman Senior Member

    What type of resin did you use?
  7. leaky
    Joined: Sep 2008
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    Location: nh

    leaky Senior Member

    It'd be really easy to smooth those out via resin, filler/putty, or fairing compound.
  8. mudflap
    Joined: Jun 2020
    Posts: 10
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    Location: texas

    mudflap Junior Member

    Thanks all, for the many replies.

    To answer some of the questions: I'm using Raka resin (127/350).

    My plan to Re-coat and re-sand certainly helped, but (on vertical sides) the resin "leveled out" some, so I ended up with an equal quantity of resin along the peak of the wrinkle and down in the valley. So I ended up spending a lot of time sanding off newly applied resin.

    Lesson learned: thicken up the resin so it'll stay put after I knock it down with the spreader.

    I added cabosil to the consistency of apple sauce and applied with a 6" spreader. This time, when I spread the resin out, there was very little on the wrinkle peaks, but the valleys remained full, so this was a big improvement.

    Another lesson learned: Dang, resin thickened with (only) cabosil is a PITB to sand!!! A little research and I read that it is best to use a mix of cabosil and micro-spheres to thicken resin. A batch of that proved to be as effective at leveling any imperfections, plus it sanded much easier (I used 2:1 cabosil:spheres).

    Last (?) question: I read somewhere that cabosil absorbs moisture?!? That's not a quality that I want in my resin!

    Is that correct? If so, do I need to top-coat with a batch of un-thickened resin? Given that I'm using the thinnest Raka resin, I'd like to be able to thicken it up a bit for use on the vertical sides to prevent runs.

    FYIW, this application is above the water line, and I only intend to thicken the resin on the vertical sides, which will shed water.


  9. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Your cabosil/spheres mix is horribly bad.

    A better ratio is about 10grams of cab and 40 grams of spheres.

    Cabosil is not hygroscopic...

    Do not use cabosil in resin alone for any fairing over 4 oz cloth. The outcome will be very impossible to sand and will result in sand thru.

    For weave filling; get a 1/4" or 3/16" nap roller.

    To fix the cloth errors, use somethi g like this ratio

    10g cab
    40g spheres
    272g epoxy

    some variation for different spheres and epoxies and temperatures would be expected

    the above mix will pinhole a bit versus off the shelf epoxy fairing compounds
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