How many layers of fiberglass cloth?

Discussion in 'Fiberglass and Composite Boat Building' started by MichaelG, Oct 12, 2007.

  1. Moosemiester
    Joined: Oct 2007
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    Location: Ohio, USA

    Moosemiester Junior Member

    Elongation of resin

    nero
    I'm working on a coastal cruising trawler, that goes all of eight knots... Previous owners used a staple gun to try to stop the delamination, then drilled holes, and shot caulk in, and filled the holes with bondo from the auto parts store!! So I expect that what I've done to cover the core I replaced will be stronger than rotted wood, bondo, and rusty staples!!

    That being said I find your comments very interesting, perhaps I've done some of the "right things" without realizing it, having never used fillers below the waterline, for instance (barrier coat additive only), but it was my understanding that a little high density filler, such as cabosil, in small quantities (just enough to make the epoxy a little less runny) made no difference in layup work. Can you elaborate on what you're saying about elongation, cloth weight, and filler?
     
  2. nero
    Joined: Aug 2003
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    Location: Marseille, France / Illinois, US

    nero Senior Member

    As I am not a composit engineer, your getting this information from the opposite end of the horse. smile Forewarned, there have been some posts about this on boatdesign.net and elsewhere on the internet.

    As I understand it, each fiber, e.g. carbon fiber, glass fiber stretches a bit untill it resists the tension force. The resine that holds this fiber in matrix and bonds it to the core needs to stretch as much as the fiber. (some of the pros quote a greater percentage) What happens if the resin is too stiff is micro cracking.

    When you add fillers to the resin, the physicall properties of the cured resin change as well as when the resin was liquid. Fillers tend to make the cured resin less strong with less stretch. There are some modifiers that toughen epoxy. (the common fillers are not among them)

    In Proboat builder, there was an artical on infusion repairs. There was a statement about not adding fillers to feather out the edge of succesive laminates.

    Cloth weight is in function of the core/skins needed to resist forces. Scantlings can give you the needed amounts. A bit more on the outside might be used for abrasion resistance.

    No microballons below the waterline. Well that is the advice I am following. It seems they may eventually fill with water. No voids, no place for water to migrate into.

    Hopefully the pros will chime in to set the record correct.

    regards
     

  3. Moosemiester
    Joined: Oct 2007
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    Location: Ohio, USA

    Moosemiester Junior Member

    ... On Fillers

    99% of my experience has been with decks and walls...

    When flexed, straight resin cracks very easily. Straight resin on 6oz cloth is strong, but not as strong as straight resin with a few hand fulls of cabosil thrown in. With 10oz or 18oz cloth it doesn't seem to make any difference, but it's easier to brush resin/cabosil that has the consistency of ketchup. It does make it harder to sand, but not as much as the warnings would lead one to believe.

    I know this because in the beginning I attempted to repair stressed areas that had bad coring underneath.

    When using low viscosity resin, like West System, the effects are undoubtedly more pronounced than when using U.S. Composites 635, which is thicker (and a whole lot cheaper which is why I use it)

    The West System High Density filler, which is probably talc, makes the resin very cloudy; plain generic cabosil does not.

    Being in the Midwest, where the boats come out for the winter, I had the opportunity to make some little test patches below the waterline a few years ago and I can attest to the fact that a low density filler after six months in fresh water is a sponge!!

    Thanks for your comments I've very much enjoyed this thread even though we have gone totally OT.
     
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