epoxy mix ratio

Discussion in 'Materials' started by idkfa, Aug 9, 2013.

  1. idkfa
    Joined: Sep 2005
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    idkfa Senior Member

    Epoxy should be mixed as accurately as possible, usually by weight, but if a mistake is made, is it better to be over or under ratio with the hardener?

    Rubbery epoxy has better peel/adhesion strength.

    tks
     
  2. tunnels

    tunnels Previous Member

    All resins of any type and especially epoxys you need to be a accurate as possible when measuring and mixing thoroughly !!, read the instructions on the containers and mix to the manufactures recommendations . There so many variations its all a bit hard to keep up with .
    Rubber fortified epoxy's stick better than most yes !!:D
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Actually, it depends. If the resin/hardener ratio is high, you need to be fairly precise, though this is a statistical issue. For example, if using a 5:1 resin/hardener ratio and you're off by an ounce of hardener, in a several ounce batch, you're likely screwed and a bad cure, if at all will occur, but if the same mistake is made with a 1:1 or 2:1 you'll probably be okay, though the physical properties might be affected to some degree.

    Simply put, if you short the resin on a 5:1 mix, you'll might be okay, but not the hardener, because a little bit off on a 5:1 is a large percentage, but a little bit off on a 1:1 or 2:1 isn't nearly as significant, especially on the resin side. Most of the usual suspects, used in the industry can be off by as much as 10% and still cure.

    This said, if you want reliable performance, try to get the mix as dead on as you can. If you must screw up, generally screw up the resin, not the hardener, as the percentage of error will typically be lower.

    Stick with what you know Tunnels. Rubber fortified epoxies don't "stick" better. This isn't an area where you'd like to discuss the merits of cycloaliphatic's over diglycidyl's or the importance of anhydrides or why thiols might be employed.
     
  4. Herman
    Joined: Oct 2004
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    Herman Senior Member

    There is 2 types of rubbery epoxy:

    -1. Rubber toughened. These epoxies contain ingredients which get the strain up, and thus peel strength. Used a lot in glues and bonding pastes.

    -2. Epoxy where the Tg is so low, it is in an elasto-rubbery state. Sometimes on purpose (great for making bumpers of race trucks), but many times by mis-calculating mixing ratios. (this brings the Tg down, but also other various properties)

    Tg = heat resistance

    Generalising:
    Too much hardener: rubbery (and less water resistance)
    Too much resin: brittle

    For gluing: use a bonding epoxy, or just a regular epoxy. Always be dead on with mixing ratios. Unless you know exactly what you are doing. It does not hurt to be precise.
     
  5. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    I use the west pump system.

    Pumps are the correct size so 2 squirts of resin needs 2 squirts of hardener.

    seems accurate enough.
     
  6. pauloman
    Joined: Jun 2010
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    Location: New Hampshire

    pauloman Epoxy Vendor

    if you are over or under ratio you have unreacted resin or curing agent in your mix. never a good thing, even if it gets hard (often you can be up to about 20% off ratio and it will still cure up (get hard)

    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 Coating)
     
  7. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    While I prefer the low ratio epoxies, I am not at all sure that one is more critical than the other in the mixing. If all molecules in any ratio mix are intended to react, then it will be the percentage that a ratio is off by and not the actual ounces of extra resin or hardener that determines how well the product hardens. Maybe Paul Oman can shed some light on this.

    As for weighing rather than measuring volumes, different epoxy resins as well as different hardeners have different densities. So you can measure by weight but the suppliers all give ratios by volume and you must know the specific weights of resin and hardener if you want to measure accurately by weight. I suspect that most marine epoxies are versatile enough to allow either though and still be good enough for our applications. There are still a few puzzles though. If you check the volumes in WEST supplied kits, the ratios are not exactly 5:1 like all the documentation says.
     
  8. wildwatson
    Joined: Aug 2013
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    Location: graham tx

    wildwatson Junior Member

    probally a dumb question.i'm building a small childrens boat and just want to coat it with epoxy.can i put food coloring in my glue to tint it?
     
  9. Herman
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    Herman Senior Member

    Epoxy, whether or not coloured, is not UV stable. I would opt for a couple of coats of epoxy, followed by a coat of 2 pack PU paint of some sort. Especially in your climate.

    Food colouring? Never tried. You might run into difficulty mixing the stuff in, but luckily epoxy is not known for attacking all kinds of stuff, so it could work. Stay away from wet colorants, however. (latex paint pigments)
     
  10. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    To color epoxies and polyester resins, you can mix in colored chalk, sold for refilling chalk line/plumb bob carpenters thig-ama-jiggy. available white, red, blue, and yellow.
     
  11. tunnels

    tunnels Previous Member

    Now be honest with your self and with us !!
    how long do you expect food colouring to last outside in the sunlight ?? also do you think it could damage the epoxy a little adding it into the mix ???? :eek::confused:
     
  12. wildwatson
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    wildwatson Junior Member

    well just thinking out loud,i want a red tint to the wood,the chalk idea sounds like the way to go.as far as how long it will last.we haven't found anything that will get red food color out(like kool aid or red fruit punch)just a idea!
     

  13. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    You want a stain.

    Google west system, EPOXY WORKS magazine.... and they have a article on variuos stains for epoxy
     
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