Does additive exist that makes cured epoxy more flexible?

Discussion in 'Boatbuilding' started by magentawave, Nov 11, 2013.

  1. magentawave
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    magentawave Senior Member

    I was wondering if an additive exists that I can mix in with EPOXY resin that will make the epoxy be more flexible? I'm not talking about more working time or curing time but I need the epoxy to be more flexible when fully cured. I'm not sure if it makes a difference to flexibility but I will be adding a lot of cabosil and 64" milled fibers to this epoxy so I can work with it on an overhead and vertical surfaces.

    Thanks
     
  2. jonr
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    jonr Senior Member

    West seems to have come up with something in their G/flex product.
     
  3. magentawave
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    magentawave Senior Member

    Thanks. Yes I am aware of Wests G Flex and also System Three's flexible stuff but both are way too expensive for what I need to do so I was hoping that there was something I could mix into the epoxy myself.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Why do you want the epoxy to be more flexible? Yes, you can "add stuff" to it to make it more flexible, but it's a give and take thing (you'll lose something else, like water proofness or compressive strength).

    The addition of silica (Cab-o-Sil) and milled fibers will stiffen the mix, so it doesn't sag, but this will not affect the flexibility of the cured matrix. I'd like to know why, before I tell you what to use to make it more flexible.
     
  5. pauloman
    Joined: Jun 2010
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    pauloman Epoxy Vendor

    yes - two options

    1) buy a flexible epoxy to start with (like cm 15)

    or add TA 661 to your epoxy

    both available from epoxyproducts.com

    Paul Oman - MS. MBA
    A.K.A. “Professor E. Poxy”
    www.epoxyfacts.com
    epoxies since 1994
    Member: NACE (National Assoc. of Corrosion Engineers) -- SSPC (Soc. of Protective Coatings)
     
  6. magentawave
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    magentawave Senior Member

    Thanks for sharing but that might be the most confusing website I have ever visited. A search on it and its epoxyusa site yields no results for "cm 15" or "ta 661". I'm really interested though and need to act fast here. Could you provide links for those products and tell me more about both of them in case they aren't explained at the website please?

    Thank you.

     
  7. magentawave
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    magentawave Senior Member

    I'm gluing wood strips to the inside of a Toyota fiberglass motorhome to act as "rafters" and "studs" which will be used as connection points to attach paneling and cabinets to and those same wood stringers will also help to stiffen the motorhomes fiberglass shell. The motorhome shell is only 1/8" to 3/16" thick and was made from a chopper gun with polyester resin from a female mold in 1982. This is for the same project in another thread I started here a couple months ago that you very generously contributed to. In fact, we spoke on the phone about it. I started this thread in case others in the future might need a more flexible epoxy. Well, after spending a lot of time working on the exterior, I am FINALLY starting to work on the interior. My reason for wanting a little more flexibility in the epoxy is so the joints can handle road vibration better. I think this could be especially important at the high load areas where the overhead cabinets will attach to when driving on rough washboard roads. I'm no expert so am I right about this or do you think more flexibility in the joints would be unnecessary?

     
  8. PAR
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    PAR Yacht Designer/Builder

    I think you're over thinking this issue. Regular formulations of epoxy will bond exceptionally well, to the old chopper RV shell. Road vibration will be easily absorbed with the stuff you currently use. Imagine a boat transom for a moment, one glued together with several pieces of wood and an external 'glass skin to keep the wet stuff out. Now imagine a 250 HP outboard (or two) attached to this transom, blasting along at say 60 - 70 MPH, flying off waves and crash landing back down. They don't use extra flexible epoxy for this and I'll bet, this is a whole lot more abuse, then your RV sides will be asked to tolerate. From what I remember of our conversation and the previous thread, you're doing fine, so no need to complicate the things, just keep going as you have and you be fine.
     
  9. magentawave
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    magentawave Senior Member

    Hah hah, me over think? No way! ;-) Okay, thanks Paul. If you don't think more flex is needed when adhering wood and then cabinets to a 1/8" to 3/16" polyester resin and fiberglass surface then I will proceed with regular epoxy. Thanks again.
     
  10. abodude
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    abodude New Member

    Found some information

    I am looking for the same information to make a wear strip on the bow and stern keel. Found this site.

    http://www.epoxyproducts.com/flex.html

    I've added charcoal and wood dust to epoxy and it became more flexible, but also thickened it. The webpage says that adding acetone will thin and make it more flexible, but maybe not forever as the acetone evaporates over time. So I wonder about adding a thickening agent such as wood dust and a thinner to make it apply better. (soak in to the kevlar)
     
  11. abodude
    Joined: Oct 2014
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    abodude New Member

    Found some information

    I am looking for the same information to make a wear strip on the bow and stern keel. Found this site.

    http://www.epoxyproducts.com/flex.html

    I've added charcoal and wood dust to epoxy and it became more flexible, but also thickened it. The webpage says that adding acetone will thin and make it more flexible, but maybe not forever as the acetone evaporates over time. So I wonder about adding a thickening agent such as wood dust and a thinner to make it apply better. (soak in to the kevlar)
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Talk to Paul over at epoxyproducts.com, he knows his stuff and I can highly recommend his products.

    I don't recommend you thin regular epoxy, without a firm understanding of the changes to the physical properties of the diluted formulation you'll create. For a rub strip on the stem, keel or a skeg, you don't necessary want a flexible formulation. In fact these elements are usually considered sacrificial in nature, so the bond should be quite weak. These pieces are typically bedded, not bonded and also they're held down with small, short screws, for the same reason, they're sacrificial. In the event of an impact, the small screws and light attachment, will cause the strip to take damage, yet fall away if it's bad enough. This is preferable to having it rigidly attached and transferring the impact loads through the strip, it's bonding and fasteners to underlying structures. Basically you want to be able to replace these rub strips, rather then repair or replace whole sections of also damaged stem, keel and/or skeg too after a hard strike.

    Lastly, all fillers placed in epoxy, alter the physical properties of the cured matrix and in most cases, some decreases in strength, stiffness, hardness, etc. will be seen. Of course, each material combination will impart different qualities to the matrix, so you'll need to do some research and testing to find a good combination for the particular task, which requires more than a casual understanding of the chemistry and physics involved.
     
  13. SukiSolo
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    SukiSolo Senior Member

    One way to make the strips is to rout the shape as a female into a board, timber, or better still acrylic sheet, cover in release agent and mould. If you get crafty you can sometimes even get the sheet to bend to simulate the stem curvature.

    Quite a lot of Classes here in the UK allow 'plastic' keel bands and bilge protecting strips. Partly to allow wooden boats to be equal to moulded GRP/FRPhulls where these features are part of the hull moulding.
     
  14. Ike
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    Ike Senior Member

    Paul, I like your analogy. But I think he has a valid concern about road vibration and slamming loads. I have traveled a lot of roads in my motorhome, and some of them I have marked off as, "I will never go there again". This is because they fit your suggested scenario. I have had to put the interior of my motorhome back together several times over the years due to these god-awful roads that produce exactly the same types of slamming you describe happening to a transom. If you want to see an example and you are ever in Louisiana take I-10 across the state. Most of it is elevated above the swamps and the expansion joints are never the same height. I had to spend a day in Mississippi just putting things back together. I experienced similar problems on some Northern California roads. I have experienced this in other states but not to the extent of those two. So this can be a very real problem in RV's.
     

  15. hoytedow
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    hoytedow Wood Butcher

    I-10 in Louisiana will shake the fillings out of your teeth. It is mile upon mile of ka-thunk ka-thunk ka-thunk ka-thunk ka-thunk ka-thunk ka-thunk ka-thunk ka-thunk... I-49 is even worse.
     
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