Dealing with air bubbles in laminate

Discussion in 'Fiberglass and Composite Boat Building' started by gary1, Jun 29, 2007.

  1. gary1
    Joined: May 2006
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    Location: australia

    gary1 Senior Member

    Evening,
    At what stage do air bubbles become a major concern in a laminate. I'm not talking large ones, the largest one is about the size of a match head and there is not very many of them. They are in the first layer of fabric which is 450 gram 15oz 0/90 Biaxial which is layed over ply. There is 3 more layers of this yet to go on and epoxy resin is being used. If these small bubles were just punctuerd with something sharp so that they would fill up with resin when the next layer of fabric is put down would that be sufficent to fix them.
    Or if they were to be ground out to say double their size with the dremell would that be the better of the 2 solutions. As I said there is not a lot of them but just looking at them pisses me off ,seems like no matter how carefull you are in laying up a section there is always a few of them to appear as soon as you turn your'e back and are half way through the next part you are trying to lay up.
    Many thank's
    Gary
     
  2. nero
    Joined: Aug 2003
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    Location: Marseille, France / Illinois, US

    nero Senior Member

    Early on, I experienced some voids when using uniaxel glass and biaxel. The fibers and strip planking were saturated but the space inbetween the tows (?) would not hold resin on vertical surface. I have resolved the problem by wetting out with unthickened epoxy and then coming back and working in a slightly thickened epoxy. Use coloidal silcia for this.

    No more voids. And the resulting surface is smooth ready for sanding.
     
  3. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    A couple of match-head-sized bubbles aren't really a concern. If you do want to fix them, simply hitting them with a small nail or punch before spreading the next layer of epoxy should do the trick (worked for me at least). I find you get fewer and smaller voids by laying the cloth into the resin, pressing it in and letting it soak up the resin from below, than you do when you squeegee the resin in from the top- but it sounds like you're already doing pretty well.
    It sounds like you're letting each layer set before adding the next. Are you doing it this way because of time constraints (ie you don't have the time to do several layers in one go)?
     
  4. gary1
    Joined: May 2006
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    Location: australia

    gary1 Senior Member

    G/Day Nero,Mat
    Thanks for the help. Nero I'm going straight onto ply I haven't really had any problems with the vertical runs yet, I put a fairly generous radius on the chines and transom edges about an 18mm radius so that hasn't really been a problem. Just these small air bubbles that appear every now and again.
    Mat, I have been wetting out the ply first then laying on the fabric and letting it soak up the resin, rollering some more resin on where I think it needs it and then hitting it with the steel roller you use for getting out the air bubbles( can't think of what it's called). There is not a lot of air bubbles so I'll give your'e suggestion a go and if I run into any bigger ones I will hit them with the Dremmel.
    I'm laying the fabric transversly as per the plan specs with overlaps along the keel of 150mm I''m actually going a bit more approx 200mm so that I can feather out the edges fairly well so as not to get raised edges along all of the overlaps. By doing this it means I can only do one side at a time, so I lay 4 pieces wait for them to cure. Then feather the edges then lay the other 3 to fill the gaps (basically lay a piece miss a piece lay a piece routine) . Then move the the other side and repeat the process. Just a slow procees that's all I don't know if all this feathering out the edges is worth the time and effort.
    I'm thinking about laying just one full side at a go and then worry about the raised edges when it comes time to fair the hull, might mean a lot more work though. Anyway only 3 more layers to go and your'e right I'm doing it on my own.
    Thank's again to both of you for taking the time help I appreciate it
    Stay Safe
    Gary
     

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  5. nero
    Joined: Aug 2003
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    Location: Marseille, France / Illinois, US

    nero Senior Member

    These small holes might be from outgassing. What time of the day are you glassing? Evening time is better as the ambient temperature is declining.

    Another solution offered here on the boatdesign.net was to fan the bubles with a heat gun or hairdryer. I tried it once with a heat gun. It works , but the resin cured too fast. Almost exotherm.

    You will soon be done with your boat?
     

  6. gary1
    Joined: May 2006
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    Location: australia

    gary1 Senior Member

    G/Day Nero,
    Mate I have been trying to lay up both times of day it has been really cold here lately so I have been trying to pick the warmest part of the day,reason being the epoxy flows a bit better. It definetly goes down a lot better when the temperature is a bit warmer it's a lot easier to work out any air bubbles. I just have to move a bit faster that's all. Thank's for the tip about the hair dryer I'll keep that in mind,moving along slowly but surely it's all good. Thank's again for your'e Help.
    Stay Safe
    Gary
     
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