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Thread: Mixing Epoxy

  1. #1
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    Sep 2007
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    Ex Sunny Cornwall UK - Now Portland NW USA
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    Default Mixing Epoxy

    Planning ahead for when it's a little warmer - I read somewhere possibly on a SOTP thread that mixing epoxy in a wider / flatter container lengthens the 'workability' time.
    How long does epoxy stay fluid enough to use whilst taping seams, probably in the cooler end of it's working temperature ?
    I am using West Systems epoxy unless you know better/easier/cheaper.
    Better to do something and regret it - Than regret not doing anything

  2. #2
    Join Date
    Dec 2007
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    West London, UK
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    Default

    hi,

    I have not used epoxy - but i think all resins are pretty much the same.

    When resin cures it produces heat (its an exothermic reaction) so if you have a pot full of it, it will get warm, which will then speed up the reaction - creating yet more heat - and therefore setting quickly.

    When you buy the resin it should come with a table of gel times - for different temperatures and % of catalyst.

    The gel time is the length of time you have before the resin starts to becomes thick and is no longer workable. You should not try to continue using the resin if it starts to gel because it wont soak in properly and will be lumpy.

    If you find resin is curing faster than you can work with it:

    a) mix up less resin
    b) use less catalyst (see instructions)
    c) work in the shade (you should not be working in direct sun anyway - uneven heating and shrinkage etc)
    d) get the resin out of the pot onto the work piece and spread it around before working it in properly.

    Yes, a shallow pot is better because the resin wont heat itself up so much because it is spread out. Its also easier to mix, I find.
    This is why its best to get all the resin out of the pot onto the glass cloth or matting BEFORE you start to work it in. If you were to work each brushfull of resin in individually the remaining resin will cure quickly in the pot, while the resin on the boat is still fluid (because it is in a thin coat) and you will end up wasting a lot of resin.

    When taping my seams I mixed enough resin to do the entire length. Started at one end roughly brushing/dabbing the resin on to the tape. I go back to the start where the resin has started to saturate the cloth and work in in properly, no need to rush because the resin is now spread out and will take a comfortable length of time to cure.

    Hope this helps and keeps you going untill some one gives (better) epoxy specific info.

    Last edited by Hobgoblin; 27th-January-2008 at 08:12 PM.
    It all started with a folding boat I built at school...

  3. #3
    Join Date
    May 2007
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    Default

    Quote Originally Posted by Hobgoblin View Post
    I have not used epoxy - but i think all resins are pretty much the same.
    Got the warning - HAS NOT USED EPOXY - Some of what follows is valid....

    Quote Originally Posted by Hobgoblin View Post
    When resin cures it produces heat (its an exothermic reaction) so if you have a pot full of it, it will get warm, which will then speed up the reaction - creating yet more heat - and therefore setting quickly.

    When you buy the resin it should come with a table of gel times - for different temperatures and % of catalyst.

    The gel time is the length of time you have before the resin starts to becomes thick and is no longer workable. You should not try to continue using the resin if it starts to gel because it wont soak in properly and will be lumpy.

    If you find resin is curing faster than you can work with it:

    a) mix up less resin
    b) use less catalyst (see instructions)
    c) work in the shade (you should not be working in direct sun anyway - uneven heating and shrinkage etc)
    d) get the resin out of the pot onto the work piece and spread it around before working it in properly.

    Yes, a shallow pot is better because the resin wont heat itself up so much because it is spread out. Its also easier to mix, I find.
    This is why its best to get all the resin out of the pot onto the glass cloth or matting BEFORE you start to work it in. If you were to work each brushfull of resin in individually the remaining resin will cure quickly in the pot, while the resin on the boat is still fluid (because it is in a thin coat) and you will end up wasting a lot of resin.

    When taping my seams I mixed enough resin to do the entire length. Started at one end roughly brushing/dabbing the resin on to the tape. I go back to the start where the resin has started to saturate the cloth and work in in properly, no need to rush because the resin is now spread out and will take a comfortable length of time to cure.

    Hope this helps and keeps you going untill some one gives (better) epoxy specific info.

    The epoxy specific bit of advice is about the the "use less catalyst" - this is a messy expensive mistake with Epoxies - unlike catalyst in polyester resins the "Hardener" component is used in, and vital to, the polymerisation reaction - if you depart from the manufacturers mix ratio - the resin will not cure and you will have a disgusting expensive sticky mess which needs to be cleaned up before you start again....

    What you can do is use a Slow Hardener - this will get you a longer "pot Life"

    The common West system has (for use with the 105 resin)
    205 Fast Hardener
    206 Slow Hardener
    207 Special Coating Hardener (I have no experience of this one)
    209 Extra Slow Hardener

    Roughly speaking - every 10C increase in temperature halfs the pot life.


    http://www.boatpaint.co.uk/acatalog/...Epoxy_209.html

    One of the tedious points about Epoxies when used as laminating resins is that the resin "slumps" rater more than polyesters do - this makes wetting out fabrics on a vertical surface a particular pain in the posterior - and worse with a slow hardener.
    Last edited by DougR; 27th-January-2008 at 08:37 PM.

  4. #4

    Default Epoxy Setting time.

    Quote Originally Posted by Slowhand View Post
    Planning ahead for when it's a little warmer - I read somewhere possibly on a SOTP thread that mixing epoxy in a wider / flatter container lengthens the 'workability' time.
    How long does epoxy stay fluid enough to use whilst taping seams, probably in the cooler end of it's working temperature ?
    I am using West Systems epoxy unless you know better/easier/cheaper.
    I was using epoxy last night for wetting taped fibre seems. The epoxy was in a pot and the temperature was 7 - 8 degrees C and I was using it for 30 minutes and it was still ok. I bought my epoxy from http://www.epoxy-resins.co.uk/. Its quick service and if you have any questions, just email the guy who runs the company, Robb Hewitt, and he phones you right back.
    Cheers, Dave.

  5. #5
    Join Date
    Jan 2007
    Location
    Calgary AB, Canada
    Posts
    103

    Default

    West epoxy is one of the more expensive (and trusted) brands as far as I can tell.

    As warned above do NOT change ratios of hardener to resin

    I use the 207 (occasionally 206) hardener, if you mix about 1/4 a cup at a time you should have no trouble wetting out the seams. It stays workable for 20min or so, mix well, but not so vigorous as to make it frothy due to generating bubbles.

    If possible 1st coat at highest day time temp, 2nd coat ofter setup, but prior to hard, about 5 or 6hrs around 20deg c for west. Then the third coat if you choose to do one can wait until the epoxy is well set, and you need to wash and lightly sand the dried epoxy prior to applying it.

    In the US Raka epoxy s a fair bit less expensive. I've been tempted, but never used it.

    good luck
    Last edited by Myrlin; 28th-January-2008 at 04:27 AM.
    So many rivers, so little time
    trailcafe.com/canoeing

  6. #6
    Join Date
    Jan 2006
    Location
    Teignmouth Devon
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    419

    Default

    I stand the pot of epoxy in a bowl of cold water to keep it from going off to quickly not sure it's good practice but it works for me.
    Many shores i have sailed to in my canoe,often against strong winds.Choose the tree well my brother if it is to carry you to distant shores. :- Chief Dan George

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