Hull fairing questions

Discussion in 'Boatbuilding' started by laukejas, Nov 2, 2020.

  1. fallguy
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    fallguy Senior Member

    Only use plastic if you need to tape a small section for repair. I use peelply a/o plastic on outside corners that are 3 planes meeting if the glass is voided there on initial work or initial tapes.
     
  2. laukejas
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    laukejas Senior Member

    What about three planes meeting on the inside, like at the front of my cockpit? Anything else that I can use as a substitute for peel ply? Plastic gives horribly waved surface that can't be smoothed out for some reason.
     
  3. fallguy
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    fallguy Senior Member

    You can do some testing of local fabrics.

    Go to a fabric store and buy 100% polyester dress liner fabric.
     
  4. laukejas
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    laukejas Senior Member

    Alright, I will try. I wonder if that peel ply helps on edges and these S-shaped curvature changes like at the centerboard. Basically the fiberglass should follow this path (excuse my horrible hand-drawing):
    upload_2020-11-10_16-47-1.png

    Would peel ply (or any other fabric like that dress nylon) help in these tight areas as well, or is it only good for large surfaces?
     
  5. fallguy
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    fallguy Senior Member

    B99C8AE9-9BFB-48BB-A8A6-05A38C3E4A09.jpeg 1B555A0F-B1C1-4CEA-888A-9218A2014AAD.jpeg 50781D6F-4777-4CC1-AFE0-AF434DAC70B3.jpeg Peelply does not expressely 'help'.

    peelply maintains a consistent surface after curing

    In hand laminating, where I use it is in places where I don't want runs and also places where I want to use tapes to hold glass patches. You don't need it unless you have problems.

    I will add a picture of a small repair to do today.

    ps...I really needed some thickened resin for the repair, but got lazy..we'll see what happens tomorrow
     
    Last edited: Nov 10, 2020
  6. fallguy
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    fallguy Senior Member

    For your centerboard; do not lay that in the same layup as the rest. Jist lay 50mm into the boat past the coaming and then lay the main glass to the edge of the trunk coaming

    For the gunwhale, the outside radius could be done with peelply and tape as it will tend to not lay nicely. But in order to do that; you would need the top of the gunwhale or inside of the boat finished in a separate go.

    personally, I would glass the gunwhale outside radius and the centerboard coaming one day and then sand any rough spots and finish the rest of it the next day...that way the centerboard is easy to reach and you can tape the peelply for the outside radius
     
  7. laukejas
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    laukejas Senior Member

    Thanks, fallguy. Due to time constrains (I can only work on weekends, and I need to get all the glass/epoxy fills with chemical bonds, so I've got to do it in 2 days), I won't be able to do things in separate gos, but I will try to at least cut separate pieces for centerboard, and glue in them in prior to the rest of the cockpit, with maybe a 4 hour offset or so. You see, I cannot remove that cloth that I laid down in the boat already. If I do, I have to throw it away. There is no way to roll it up nicely and then hope to put it back into it's original place. So anything involving sanding (which would ruin that cloth with dust) is out, I have to do it all wet, so to speak. You see, I am trying very hard to avoid sanding glass. I have done it before, and nearly scratched myself to death afterwards, even with a full body suit and a respirator.
     
  8. fallguy
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    fallguy Senior Member

    I understand. I hate glass fibers in my finger webs with a passion.
     
  9. Blueknarr
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    Blueknarr Senior Member

    Why the necissaty for chemical bonds?

    Your plywood hull is structurally sound with out needing the glass coat.
    The fairing compound you already applied is mechanically not chemically bonded to the plywood.
    At your working temperature epoxy takes months to fully cure.
    Working pieces of glass can still be done in one weekend.
    The next layer of fairing will bond sufficiently well even if a month goes by
     
  10. laukejas
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    laukejas Senior Member

    Well, chemical bond is much stronger than mechanical one. I had de-laminations before where epoxy got unstuck from the previous layer of epoxy because it wasn't roughed up enough. I am not entirely sure how long does epoxy retain the ability to bond chemically. Some say 5 hours, some say 24. In cold temperatures it might be towards the longer end, but I don't want to risk it. The fairing compound is bonded chemically to the plywood, because I saturated all the plywood with liquid epoxy before adding fairing compound.

    Sure I could stretch this out if I had more days, but I only have 2 per week. And I do not want to wait 5 days before the next coat - might not get bonded chemically. So I would have to sand it just to be sure, and then... Fiberglass splinters everywhere.
     
  11. Blueknarr
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    Blueknarr Senior Member

    I understood your concern especially after having a bad experience.
    One epoxy I used years ago had a cure chart that went something like:
    90 °=1 hour
    80°=6 hours
    70°=24 hours
    60°=72 hours
    50°=5 days
    40°=30 days
    30°= no cure

    Of course the chart will be slightly different for the brand you are using. But it will follow a similar pattern.

    Your fairing took at least a week to become "sand able". And then it was gummy. An indication that it was still open to chemical bonding.

    You have more time than you think.
     
  12. laukejas
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    laukejas Senior Member

    Very interesting. I will contact my epoxy manufacturer and ask for a similar chart. Well, I'll see what can be done then, perhaps I will be able to split this job into several parts. But even if I would do the centerboard trunk separately, I am not sure how to add plastic sheeting and sticky tape to compress that fiberglass everywhere. No way to reach into the trunk itself to put tape there. Well, maybe it won't be as bad as I fear. Perhaps I can make do with simply pushing fiberglass back into position as epoxy cures.
     
  13. fallguy
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    fallguy Senior Member

    I have an idea for your centerboard trunk.

    if you make a jig that sets down into the trunk and you cover the jig with shipping tape; it would hold the glass down

    This type of thing is done all the time for vac table work when you have to plug under the part. Basically, you'd take a piece of wood the size of the trunk less space for ship tape and glass and another piece of wood overtop. Then you can decide if you want a wee bit of radius or not by filleting the jig.

    The centerboard is basically female and the jig is male. Just make sure to ship tape all surfaces of the jig/plug.
     
  14. laukejas
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    laukejas Senior Member

    Thank you for that idea. I had a jig prepared, but turns out, it was not needed. The glassing went far, far better than I expected. Cloth had absolutely no difficulty making these turns, and once wetted enough, it stuck in place and didn't even think about lifting off. The hard part was actually not disturbing these large pieces of cloth, and making sure fiberglass doesn't bridge anywhere or doesn't leave air pockets. I spent 6 hours wetting out that cloth, and a few more hunting down these air pockets, picking a hole in them, and then pushing them flush with the surface. The only disappointment was the ungodly amount of epoxy that I used. I was very conservative with the first coat, using squeegee to collect any excess resin, pushing hard to squeeze out as much as I can, and then move it to dry areas. And yet I must have used at least two pounds of epoxy just for that initial wetting out. After 12 hours, I started applying filling coat with a thick microballoon epoxy mixture. I used some food wrap on the sides of the boat so I could lean into the cockpit without ruining my clothes or the fiberglass.

    Before fill coat:

    [​IMG]

    After fill coat:

    [​IMG]

    [​IMG]

    [​IMG]
    [​IMG]

    I tried the notched trowel to spread epoxy evenly before pushing it into the weave of the cloth with a spreader, but even the smallest-toothed trowel I had was not nearly small enough to provide that minimum amount of epoxy needed, so I had to push the damned goo with my spreader again, eye-balling it. It was exceptionally difficult to get an even thickness. In some places I found that using my fingers (with gloves, of course) was the best way to get epoxy to go where it needs to. Like in that last pic of daggerboard trunk.

    In any case, I failed to completely fill the weave, mostly because it would have required an insane amount of epoxy. So for this coat, I went with the minimum possible, and for tomorrow, I am going to 3D-print some new notched trowels with even smaller teeth. I get this feeling that once I get to sanding, I will inevitably sand into the cloth again. It is very difficult to tell where I need to apply that epoxy to hide the weave completely, without going overboard. Epoxy is expensive and heavy, and I need my boat lightweight.

    Any tips on how to save on epoxy to fill that cloth and build enough thickness so I can sand it without digging into fiberglass? I am already using microballoons, they increase the volume of epoxy at least 3 times, but even then the amount needed to cover everything is insane. I figure at least 1/3 of my boat's weight is going to be epoxy by this point.
     

  15. fallguy
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    fallguy Senior Member

    Epoxy use needs to be about 100% of the weight of the cloth.

    So, the cloth say at 10 oz per yard.

    Measure the total square inches of glass and add for overlaps.

    Divide 144 to get to sqft.
    Divide 9 to get to yards.

    say you have 3 yards glass; you need 30 oz epoxy by weight or say 1.9 pounds

    1.9 pounds epoxy
    Divide 9 pounds per gallon is 1.9/9*128 liquid oz per gallon or 27 liquid ounces epoxy. However, all raw plywood deserves prewetting at 2 oz per yard, so that would be 6 more. Then roller losses are 4-8 ounces, depending on the roller. I squeegee the roller out on dry spots at the end..

    As for tips, I already have an idea what your issue might be. Epoxy works best when the ambient and boat and epoxy temps are about 75-80F. Colder than that and the epoxy gets too thick and is impossible to wetout and the result is overuse of resin.
     
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