Glassing a 3.6m plywood hull

Discussion in 'Materials' started by AshleyC, Mar 29, 2019.

  1. AshleyC
    Joined: Mar 2019
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    AshleyC Junior Member

    Hi all,

    I'm new to the forum and happy to be part of this community! I'm currently building a Selway Fisher TAW, a 3.6m plywood roundabout as a "learning project" for future bigger projects.

    I'm having some issues with fiberglassing the hull (having already applied and had to sand away fiberglass, I don't want to have to do it again!)

    I'm planning to precoat the hull with epoxy (I'm using west systems 105 and 206), then lay on the fiberglass (tricky with a precoat I know) then wet out, then fill the weave with thickened (low density) epoxy, then fair with the same thickened low density epoxy.

    I know there is a lot of discussion whether or not precoating is necessary but I have done tests without precoating and you can too easily (for my liking) peel the fiberglass from the ply.

    The bit I'd need advise on is whether i can fill the weave with thickened epoxy or must i apply 2 to 3 layers of unthickened epoxy. I'm not going for a clear coat so there's no issue there.

    Also, whatever I do, I get bubbles in the cured epoxy, I have attempted the roll and top method many times but bubbles seem to form anyway. This is layer upon layer, sanding each previous layer smooth... to no avail. Any tips? I'm working at around 15-18C°.

    Would I then have to coat the thickened epoxy in unthickened epoxy before the primer and paint or could I apply primer directly onto the cured thickened epoxy?

    I apologise such a long initial post and appreciate your help

    Thanks!
     
  2. fallguy
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    fallguy Senior Member

    --->. Precoating is required. There is no debate. Dry sucked glass is a fail.

    ---->. Neat coat at about 2 oz a yard is easy. Fairing is only done where there is a deeper area. I would fill deep places first; then neat coat with up to 3 coats. Done fast enough, you can avoid sanding if the epoxy does not blush.

    ---->. The best way to reduce bubbles is the right epoxy. The 2nd way which is lousy is a warm water bath.

    ---->. You have to sand to create teeth for subsequent layers. Otherwise you lost me.

    Also, you can work wet on green. That means as long as the epoxy has not blushed; and is only partly cured; you can apply another layer of glass without sanding.
     
  3. JamesG123
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    JamesG123 Senior Member

    Reading between the lines of your post (bubbles and wanting to uses thickened epoxy) you may be using too course a glass ply and/or attempting to use too large a piece at a time and thus getting tension around corners and compound curves that is causing the fabric to lift off the surface before the resin has had a chance to go off and set. You can get away with "sloppy" layup when vaccum bagging because the pressure squeezes the glass down, but not doing a hand layup.
     
  4. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Welcome to the group

    A few questions

    Are the bubbles random or do the align with the wood's grain or the fabric's weave?

    Pinhole bubbles or largish blisters?

    Are you using a bubble buster roller?

    What weight and weave of fabric are you using?

    Heavier fabric or one with a pronounced weave will require more fairing compound. Depending on your cosmetic expectations, a light fabric may not require extensive fairing.

    Pictures would help.
     
  5. AshleyC
    Joined: Mar 2019
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    Location: Mojacar, Almeria, Spain

    AshleyC Junior Member

    Thanks for the replies guys!
    I think I've decided what method I'll be using, here are some videos of the epoxy bubble problem.

    The glass was laid dry, then wet out, left 6 hours, then the weave was filled with 3 or 4 coats (6 to 9 hours between each coat). You can also see me peeling the glass, arriving at the conclusion that a precoat would be necessary.



     
  6. JamesG123
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    JamesG123 Senior Member

    Ok you mean the surface bubbles? Try using a foam or hair brush slowly.... Those are artifacts of drawing a brush or roller stroke too fast and the viscosity of the epoxy trapping air as you do so. Spraying and/or using a thinner resin for a top coat will stop that even more.

    Edit, cause I can't multitask on one cup of coffee.
     
    Last edited: Mar 30, 2019
  7. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    I've also seen people in youtube videos use heat guns or blowtorches to expand and pop surface bubbles in epoxy, but I'm not sure if that is recommended for boats.
     
  8. AshleyC
    Joined: Mar 2019
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    AshleyC Junior Member

    Ahh, I did tip rather fast, with both foam and hair brushes. Thanks! I'll give it a go slowly.

    I remember reading that you can't spray epoxy, do you know otherwise? And do you know any examples of thinner epoxy brands, maybe west systems is notoriously thick. Cheers!

    Yes, I've tried this but seems to burn the epoxy very quickly... maybe I'll try and again with a more patient approach.

    Thanks again guys!
     
  9. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Epoxy can be sprayed, but it introduces a whole new set of problems. Generally, while laminating it is easier to manually spread than spray.

    I have toothpicks on hand to pop the occasional bubble.

    Hair dryers are less likely to burn than flame throwers. Beware of dragging the cord.

    Laminating resin should be thickish. Thinning them down weakens them.

    Good luck
     
  10. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Side bets the bubbles are outgassing.

    Pay close attention to temperatures; research outgassing and temperatures. I am not an expert because I have only had it happen using a certain epoxy and I have no desire to mention the epoxy. I am not unwilling to tell you Systems 3 Silvertip has been designed to prevent outgassing.

    A bubble buster roller is great advice for bubbles introduced when laminating.

    Also, basic rules of rolling only into inside radiuses and away from outside radiuses can help a tad with laminating bubbles.
     
  11. fallguy
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    fallguy Senior Member

    Video 2 is outgassing of something.

    Outgassing of the epoxy itself or a chemical used to clean the plywood.

    Or outgassing of a glue in the plywood.
     
  12. redreuben
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    redreuben redreuben

    Don't apply the epoxy when the air temperature is rising like in the morning, apply when the temperature is falling and you won't get the pinhole bubbles as air escapes the wood.
     
    Dejay and fallguy like this.

  13. AshleyC
    Joined: Mar 2019
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    AshleyC Junior Member

    Thanks guys, really helpful info, I'll apply these methods and get back to you with results. Thanks again!
     
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