Does a fast drying and easy to sand filler exist that adheres to epoxy?

Discussion in 'Materials' started by magentawave, Jan 20, 2014.

  1. magentawave
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    magentawave Senior Member

    Does a fast drying and easy to sand filler exist that will adhere to epoxy? Bottom line is that I'm looking for something similar to Bondo that will adhere to epoxy.

    Thanks!
     
  2. pescaloco
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    pescaloco Senior Member

    System 3 Quick Fair about 3 hours at 75 F

    Don't know of anything like Bondo for epoxy
     
  3. magentawave
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    magentawave Senior Member

    Looks good, but dang, a 1.5 quart kit is about $50.00...aargh! Could I make my own out of microballoons and epoxy? By the way, are microballoons with epoxy easier to sand than cabosil with epoxy?
     
  4. gonzo
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    gonzo Senior Member

    Yes, much easier. However, they are not too good for below the waterline.
     
  5. PAR
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    PAR Yacht Designer/Builder

    If you do a lot of fairing, mixing your own is the only economical route. You should log onto WestSystem and SystemThree and download their texts on mixing fillers.

    Silica (Cab-o-sil) is about as hard as it gets. A fairing mixture is nothing but light weight materials (Q-cells, talc, balloons, etc.), with just a touch of silica to control viscosity. If you want to sand it reasonably quickly, use a fast hardener, though your working time will be shortened too. I'm not sure where you are, but you can expedite an epoxy cure with heaters under a tarp.
     
  6. magentawave
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    magentawave Senior Member

    I've been using a lot of cabosil on this project and you are right that it is insanely hard. I'm in north San Diego county on the coast and will be picking up some microballoons today.

    Thanks
     
  7. PAR
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    PAR Yacht Designer/Builder

    Use lots of talc (yep, baby powder) to make sanding easier.
     
  8. missinginaction
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    missinginaction Senior Member

    PAR's baby powder advise was a game changer for me. I was filling inside corners on a flybridge I was making when he suggested talc to me. Suddenly doing fillets became almost enjoyable. I started mixing about 50% silica and 50% talc. This worked but as time went on I kept increasing the talc. I finally ended up with about 75/25 talc to silica (by volume) or less depending on temperature. I figured that I needed just enough silica to keep the mix from slumping under it's own weight.

    BTW, when doing corners another really helpful tip is the use of rubbing alcohol on a gloved finger. Once your resin starts to harden, but is pliable, you can use this technique to smooth out awkward areas and save yourself a lot of frustration. Again this tip came from Paul and I'm just repeating it. It's a great time and effort saver. Might not help for fairing flat surfaces but remember it. At some point it will come in very handy.

    MIA
     
  9. magentawave
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    magentawave Senior Member

    Thanks for the tip about using rubbing alcohol with a glove because I need to make some clean looking fillets very soon! Is cabosil the same thing as silica?



    You mean regular ol baby powder that I can buy at Walmart? Do you mix anything else with the epoxy and talcum powder? If so, what are the percentages you recommend?

     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Talc is a mineral and most fibreglass/resin suppliers stock it. Used in car bog, so obviously it sands well. Hollow sphere filled resins aren't as good a base for painting, a slick finish is more difficult to obtain.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Yes, baby powder works and you'll smell good afterward too. I get talc in bulk, less the fragrance.
     
  12. magentawave
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    magentawave Senior Member

    Do you mix anything else with the epoxy and talcum powder? If so, what are the percentages you recommend?

     
  13. PAR
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    PAR Yacht Designer/Builder

    Again, download the free user's guides from the major formulators.

    Each mix is dependent on several factors, so percentages are meaningless. Once you learn what each material does, you'll have an easier time figuring out what to use. There's also an experience factor involved.

    Silica (cab-o-sil) is best used to control viscosity, so you usually don't need much. Fairing compounds are all light weight materials, that also are easy to sand. Each mix, regardless of application will usually have more than one material in it.

    Fairing compound will be mostly the light weight materials (balloons, Q-cells, etc.) with enough silica to get it to do what you want. So, if you need to make fillets, you'll use enough silica to make a peanut butter consistency, but on flat surfaces, you'll only use as much as you need to keep it from running or sagging, which may be like a runny ketchup or heavy cream like consistency. Each batch will be custom mixed for the job at hand.

    Now, you can premix fillers, which is what I do, each having different physical qualities. I store these in gallon jars and dump out what I need, depending on the job. I'll add silica to get the viscosity I want. A heady feature of this technique is consistent batches, but you have to justify mixing up large quantities of filler materials for this approach.
     
  14. magentawave
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    magentawave Senior Member

    I have pre-mixed lots of large batches of thickened polyester resin and use it as I need it cuz you don't need to be exact when adding catalyst to polyester resin. But lets say I pre-mix a quart of thickened epoxy resin and only want to use a little bit of it now, how do I know what is the correct quantity of hardener to add?

     

  15. pescaloco
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    pescaloco Senior Member


    Hey we are neighbors I live in South Bay

    Yes the quick fare is expensive, far cheaper to mix your own
    The advise given by OP's on fillers is exactly what you need to know
    I think its a pain to mix small quantities of epoxy filler that's why the Quick fair is nice but if you are doing some serious filling and fairing get micro balloons, Talc and fumed silica (cabosil) and your all set

    What are you working on ?
     
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