Thickened vinylester not setting

Discussion in 'Materials' started by Brentmctigue, Sep 16, 2021.

  1. Brentmctigue
    Joined: Apr 2015
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    Brentmctigue Junior Member

    Hello
    I’ve been using vinylester resin thickened with cabosil for coves. It is taking days to set. Days are 20+ degrees C, nights down to 3deg. 70-95% humidity.
    What am I doing wrong?
     
  2. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    How are you catalyzing it?
    How much are you mixing at a time?
    What mixing containers are you using?
    Is it firm and sticky or soft and squishy?
    What brand?
    Any suffocant used?
     
  3. Brentmctigue
    Joined: Apr 2015
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    Brentmctigue Junior Member

    MEKP just under 2%
    200ml to 900ml
    Coving I usually mix to a thick peanut butter consistency. Still has a slight sheen to the mix. Scottech vinylester PQ Australia Q-Cel. No suffocant. Don’t know what that is?
    Cheers Brent.
     
  4. ondarvr
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    ondarvr Senior Member

    Is just the surface tacky, or is the entire mix, even what's left over in the container soft for days after you catalyze it?
     
  5. Brentmctigue
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    Brentmctigue Junior Member

    Yes the entire mix is uniform. The left over in the ice cream container is still going off after days as well however it seems to set quicker than the coving.
     
  6. ondarvr
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    ondarvr Senior Member

    Either the resin is unpromoted, or your catalyst measurements are off.

    VE resin is frequently sold without the additives that cause it to cure in a normal amount of time.

    The additives tend to lose their effectiveness rather quickly compared to polyesters, so the shelf life can be short for VEs.

    They are commonly sold without those ingredients and they're only added shortly before being used.
     
    DogCavalry and fallguy like this.
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    That is interesting, what ondarvr says about VE, I didn't know about either matter, the lack of additive or the shelf life, useful to know, this man is a fund of information about reinforced plastics !
     
  8. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    you are mixing the solution first then adding the cabosil later, yes?
     
  9. F.G. Dragonfly
    Joined: Sep 2021
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    F.G. Dragonfly New Member

    I am going to bet you have the wrong MEKP catalyst some VE's have the own which is hotter than you're using, check with the manufacturer of the resin.

    Do you have the right catalyst for the VE.....the MEKP might not be hot enough or it takes a certain type.

    I worked for a boat builder and a new man layed up a console I asked the owner which cata
     
  10. ondarvr
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    ondarvr Senior Member

    VEs don't require a special catalyst to cure, a certain type of catalyst is recommended to prevent excess foaming though.

    Some types of MEKP have a higher hydrogen peroxide content, it reacts With the VE resin and foams. The recommended catalyst has a lower percentage in the formula. It still foams, just less.

    You can get a different degree of cure with certain catalysts, but this would only be identified by lab analysis.
     
  11. ondarvr
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    ondarvr Senior Member

    Some do mix the catalyst in first, but 99.9% of all polyester and VE putties are pre-thickened, then catalyzed at a later date.
     
  12. F.G. Dragonfly
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    F.G. Dragonfly New Member

    I didn't say special catalyst, I said a hotter catalyst. The gentlemen can make a phone call and within a short time will know if his MEKP is not the right MEKP to use in that VE.

    All the filler and undercured VE is junk and needs to be replaced with properly cured resin and filler that takes a couple of hours and not days to cure.
     
  13. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    It doesn't need to be a hotter catalyst to cure.

    VE will cure with any of the typically available catalysts, the low hydrogen peroxide versions just don't foam as much.

    The term "hotter" for some of these catalysts is due to the lower peroxide content. The peroxide reacts and starts the initial cure sooner, this is where the foaming comes into play.

    Reducing the peroxide content extends the initial cure, but that creates a somewhat steeper cure profile at the end of the cycle. This may result in a higher exotherm, so they may be called hotter at times.

    Old school VEs had a somewhat sluggish cure, the surface would be sticky, so you used the 'hotter' catalyst to help kick it in the butt.

    VEs will also cure well, and typically have higher physical properties when used with some very slow and let's call them "cool" catalysts.
    These blended catalysts foam less, have long gel times and very low exotherms.

    The uncured putty has nothing to do with the catalyst type, it could be from old catalyst or the wrong amount though.

    Again, you wouldn't notice any difference in catalyst type as to whether it cured or not, in a lab you may be able to detect the small differences in the physical properties.
     
    Last edited: Sep 25, 2021
  14. F.G. Dragonfly
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    F.G. Dragonfly New Member

    If you bought a 1liter or a 5liter pail, it will be promoted. Drums will come unprompted but a fabricator will ask for that specifically. Unprompted has a longer self life.

    You never said the brand of catalyst you're using, Curox MEKP ranges from 100 -300 with numbers in between. Some have more water content than others as well as peroxide % and promoters. A phone call to Scot Technology will help you.
     

  15. Brentmctigue
    Joined: Apr 2015
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    Brentmctigue Junior Member

    Guys,
    Thankfully all for your replies. I’ll check with the manufacturer and get back to you on the MEKP.
    Spring has finally spring here in Australia so the reason is going off as per usual. In some instances sandable within a few hours so happy days. I still want to know what went wrong so will do more research with the manufacturer and let you know what I come up with.
    Cheers
    B
     
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