HELP! Gelcoat cure question

Discussion in 'Fiberglass and Composite Boat Building' started by thill, Mar 2, 2012.

  1. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    I decided to fix a number of little chips in my boat. I mixed the color and the hardener and applied. Everything was looking really good.

    This morning, all the spots were still wet. It didn't gel at all! ARRRGGHHH!!!!

    What do I do to make it set up???

    Obviously, I could clean everything and start over. But THEN, then I had an idea....

    COULD I put a drop of catalyst on each spot and then cover with plastic film to seal it in? Would that work, or is there something wrong with my gelcoat?

    Does gelcoat go bad? I've had it for about 6 months.

    Thanks in advance for any help!

    -Tony
     
  2. iceboater
    Joined: Jan 2011
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    Location: Iceland

    iceboater Junior Member

    The only correct way of doing this is to clean it and start again. But first, do a gel test on it before you use the same gelcoat again. If it has to long gel time (more than 25-50min), you can probably get accelerator from your supplier to fix it.
    Gelcoat does go bad but it is unlikely that it is bad after 6 moths if it was bought "fresh".
    Since you are probably using very small amount of gelcoat to fix these chips, I would recommend using syringe to measure the catalyst at 2-3%.

    Axel
     
    1 person likes this.
  3. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    Okay... I decided to give it a try. I put a drop of MEKP on a chip repair, then smoothed a piece of Saran Wrap over it.

    It's been about an hour, and I went back out to check, and one spot seems hard, the other seems rubbery, but definitely not wet like before. I think it's working!

    This brings up another question... Will the MEKP on top produce just a surface "shell" or will it cure all the way through if I leave it on overnight? All the repairs are 1/8" deep or less.

    Thanks.

    -Tony
     
  4. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    Iceboater,
    Sorry! I was typing when you made your reply.

    Thank you for the clear thinking. Getting the color right was a pain, but it's only a small amount of gelcoat. I should clean the spots, mix again, and double the amount of hardener. (2%)

    Will report what happens. Thank you.

    -Tony
     
  5. tunnels

    tunnels Previous Member

    Small quantities of gel coat !! IS REALLY EASY TO OVER CATALYST small quantities of gelcoat and to much is as bad as to little so mix a bigger amount and put in just the same amount of catalyst!!! .
    do a sample and see what happens .
    Remember the catalyst will also change the colour of the gel coat slightly !! so it will never match perfectly no mater what you do . Time will fade the old and the new will slowly blend in but with all takes time !!. :D:p:):p
     
  6. pescaloco
    Joined: Feb 2006
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    Location: so. california

    pescaloco Senior Member

    I would recommend to start over.

    A couple things though

    1. mepk catalyst goes bad when too old
    2. gelcoat needs a surface seal of some kind to inhibit air on the surface.
    usually a material called surfacing agent (wax/styrene) or P V A
    3. use an eye dropper to catalyze small quantities 20 drops of mekp per
    ounce of gelcoat will give you 2% ratio at gel time of 20 to 30 minutes at
    75 degrees F
     
  7. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    Tunnels,
    That's why I was so bummed about it not setting up! I nailed the color, just right! The spots literally disappeared when I put them on! I had to search for them afterward!

    I've never nailed a color like that before, and it figures, I didn't put in enough catalyst! ARRRGGGHHH!!!!!



    Pescaloco,
    You just told me what I needed to know. Thank you! I made about an ounce, but only put in 7 drops of MEKP. I never knew that MEKP goes bad. I have a sealed tube of it that I bought last summer. Should that be okay?

    I've used Saran Wrap to keep the air off in the past, and it works well. I've also used the PVA, but I like the plastic film better for chip repair. Thanks again for the help!

    -TH


    Tomorrow is supposed to be a nice day. Will give it another try.
     
  8. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    If you used 1% of catalyst, as I might read from your comments, then that is WAY too little. Use at least 2% for a gelcoat, or it should be very hot. 3% is the max, approximately.

    The now applied gelcoat is undercured, and the residual styrene WILL yellow over time, ruining your colour matching job.
     
  9. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    Herman,
    Thanks for the further info. I now plan to clean out the spots and start all over again. The ones that felt hard on top were not cured all the way through.

    This time, I will make an ounce, and will put in 20 drops of MEKP from a sealed tube. Will post my results. Thanks.

    -TH
     
  10. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Stop. A MEKP tube? You mean the white or red paste-like stuff? That is BPO paste.

    Good news is that it is simple to store and mix mechanically, but water resistance is impaired a bit.

    MEKP is a watery, usually colourless liquid, which can be dispensed with an eye dropper.
     
  11. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    No, it's MEKP. It came from US Composites, and it's in a little tube. You pierce the tip, and dispense it by the drop. It works nicely for smaller amounts. I also have a bigger bottle.

    I've used the pink cream stuff before, (like in Bondo) but this is definitely MEKP.

    Didn't know the cream caused water resistance issues. Good to know. Thanks.

    -TH
     
  12. latman
    Joined: Mar 2010
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    Location: Australia

    latman Junior Member

    Did you have wax in it ? (sold here as wax in styrene) it either needs that in it so it can completely cure in air and be sandable (Flowcoat) OR you need to spray something like PVA over the gelcoat to keep the air away from it (I recomend blue coloured PVA so you can see the coverage and then you can use it as a "guide coat" for sanding also (the hollows will stay blue) I guess there is a chance the PVA dye will stain the repair so it might be worth staying with clear ?
     

  13. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    Done!

    Thanks to everyone.
    I scraped off the patches, then cleaned with acetone.

    Did another color mix, then counted drops of MEKP. Applied to the chips, then smoothed over with saran-wrap to seal air out.

    Came back an hour later, and they were DONE! The plastic film even left them smooth, so I didn't even sand most of them. Just hit them with 3M restorer wax and the buffer the next day. Not even sure I hit them all because they simply vanished!

    As usual, thanks to you for your experience and helpfulness!

    -TH
     
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