Realy realy dumb question I think

Discussion in 'Fiberglass and Composite Boat Building' started by Frosty, Nov 4, 2011.

  1. Frosty

    Frosty Previous Member

    If I was to use fibre glass resin do I need to use fibre glass mat. Try to keep the laughter to a minimum but could you use other material like cotton or denim, sacking or anything like that. Ive done it in very very non sensitive places like I once glassed in an old sock into the floor of and old car I had and I was surprised at how well it worked .

    What about an old blanket or some curtains matting is very expensive.

    So to recap,-- can you use any material with fibre glass resin?
  2. rwatson
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    rwatson Senior Member

    I was talking to a guy yesterday who is going to epoxy some coloured textiles, and infuse them onto a wooden knife handle.

    Poly or Vynil Ester would work to a certain extent, but not glue as reliably.
  3. Manie B
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    Manie B Senior Member

    Not so dumb
    I have used cloth
    old "T" shirt works ok
  4. daiquiri
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    daiquiri Engineering and Design

    The question is not so trivial as it seems at a frist glance. Cotton flocks are used as a filler for epoxy - see this thread, for example:

    However, cotton flocks work because they are tiny flocks and not macroscopic fabric. They have a high tensile strength, meaning that it takes a very huge force to elongate a single cotton strand (or flock) by a small amount. On the other hand, a cotton fabric doesn't have this characteristics. Take your t-shirt and pull it apart - you'll feel how it yields elastically a great deal before starting to oppose a real resistance to your pulling force.

    What it all means is that, in a laminate made with t-shirts or socks :D only resin will work and resist the loads, the fabric will at most be a reinforcement against brittle failures.

  5. hoytedow
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    hoytedow Carbon Based Life Form

    I covered a boat with cotton cloth printed with Budweiser emblem, over fiberglass. It was purely decorative. It came out lousy. The ink ran.
  6. hoytedow
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    hoytedow Carbon Based Life Form

    There are no dumb questions, just dumb answers.
  7. yipster
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    yipster designer

    sure you can, ive used chalk, micro balloons and fibers, cloth, etc for some have to think deep reasons. but why would you?
    glas has long fiber, is strong, cheap etc. carbon and epoxy would top its mechanics but cost more and is a bit harder to work with
  8. Frosty

    Frosty Previous Member

    Ah --that makes sence.
  9. SamSam
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    SamSam Senior Member

    You can use other materials, some are better than others. Some soak up lots of resin, I read of a third world country using cheap resin and burlap for roofing. Some are weak. The strength of composites come's from the cloth material, mostly. Some won't bind to resin very well, some will easily break when bent, or tear when pulled or when you try and rip them. It's easy enough to experiment with a bunch of 6" squares and put them to the test. Most designs won't run, you can have paisley or striped repairs or boats, if you want.
  10. tunnels

    tunnels Previous Member

    Skinned a boat with a bed sheet and epoxy ! worked well and nice finish!
    Have moved on from those days mind you !:p
  11. rxcomposite
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    rxcomposite Senior Member

    It's not really a dumb question after all. Lesser strength organic fibers are being used nowadays.

    In the mathematics of composite called "Rule of mixtures" the resin and fiber are combined together to get a reasonable strength of the material. If you combine fiberglass and the "brittle resins-polysester" you get about 10 to 12% of the strength of the glass. Why, because the glass is very strong and the resin fails first. When one of the component fails, the laminate is said to be failed.

    So by combining the weak resin with weak materials like jute sack, bamboo fibers, or sisal fibers, you get a composite that works in synergy, by failing almost at the same time. Weaker, yes, but economical and it works.
  12. Frosty

    Frosty Previous Member

    Under what circumstances and or application would you want a lesser result in strength.

    I guess strong enough is all thats required but too strong is inconsiquential.

    An aircraft wing perhaps?
  13. cor
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    cor Senior Member

    The old Trabant cars made in Russia used wool as the fiber in the body panels.

  14. PAR
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    PAR Yacht Designer/Builder

    RX has got it, you try to match "reinforcement" elongation, generally, in the cured resin matrix. Naturally, there are other physical considerations, but essentially, the reinforcement fibers, whatever they may be, should be close to the modulus of elasticity, in the cured resin system employed, whatever that may be.

    The idea as RX points out, is to get the fibers at their breaking point, about the same time as the resin reaches the same set of issues. This means you're not "wasting" reinforcement or resin properties. This is why it's silly to use mat with epoxy. The mat will tear and break long before the resin is ready, so you have reinforcement failure and are carrying an expensive resign system along for the ride, just because you like to toss material's money out the window.

    It's this same logic that cause a builder to use spherical shaped (microscopically) reinforcements when lots of sanding is required. You need the combined resin/reinforcement combination to abate at a reasonable rate, for ease of use (shaping usually), so light weight, minimal surface area particulates are employed.

    Matching a laminate's physical qualities with the loads, needs or uses is the whole point behind composite construction and also why it's such a highly engineered process. There are rules of thumb, such as fairing and fillet mixtures, but otherwise, you need to think about every square inch's physical requirements.

  15. Herman
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    Herman Senior Member

    Trabants were made in the DDR, not Russia. The fiber was flax. They were also made in Egypt, but the fiber was changed to glass, as the goats ate the bodywork.

    At this point there is a lot of energy put into green alternatives for composites. Among them all kind of natural fibers: flax, hemp, etc.

    About 10 years ago we laminated T-shirt cloth in a boat, to get the view on the outside. (loggers pattern), which looked OK. Hard to de-air though.
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