Mixing epoxy

Mixing epoxy

Raw Notes #

This is a temporary page containing raw, unedited notes on this subject. This page and the information here is incomplete, and may be inaccurate.

  • Add in some of the good generic info on what epoxy is, how it cures, thin film vs 100g in a pot, splitting it and spreading it over the glass first, splitting the rest, etc.
  • Tinting the hardener to learn if you’re mixing well.
  • Get a video of the entire mixing process.
  • Get everything ready beforehand. See my checklist. Scale, cups labeled with how much each of resin and hardener you need in each, stir sticks, paper towels, extra gloves, hammer to close the cans, tool to open the cans, etc.
  • Mix by weight whenever possible, but see the epoxy specs to be sure. I use a scale accurate to 1g. I’ve read at least one epoxy spec sheet that said to mix by weight within 5% of goal. I go for within 1g, because why not.
  • Two cup mixing method:
    • Measure your hardener into one cup, and your resin into another.
    • Pour the hardener into the resin, and get as much out as you can quickly.
    • Stir well for 1 min.
    • Pour the entire mix back into the hardener cup. Scrape the resin cup well, ensuring you get all resin out of the bottom edges.
    • Stir well for 1 min, being sure to scrape the sides and bottom edges well at least once.
    • Profit.
  • After mixing, I pour half of my mix into a 3rd, clean cup, usually a plastic party drink cup. This divides the mass of the mix and helps keep a control on heat and pot life.
  • I then pour the remaining half of the mix, still in the hardener cup, onto both glass layers. I then pour half of what’s in the party cup back into the hardener cup, so I end up with 1/4 of my mix in each cup ready for the rest of the layup process. I then go back and spread the resin I poured on the glass well, and go on from there. As I layup, I take mixed epoxy from each cup alternatively until it’s all gone.
  • Pot life: this is typically specified as the time it takes for 100g of mixed epoxy to set at 77F. Increase the temp or the volume, and your pot life shortens.
  • Thin film set time: this is typically specified as the time it takes for a thin film of spread epoxy to set at 77F, and is usually much, much longer than the pot life. You can relax once you’ve spread all of your epoxy into a thin film.
  • Do not artificially heat your epoxy to make it flow better, or easier to mix, or whatever. Keep it at room temp and use it from there, ideally around 70F. Only apply heat once it’s in the press.
  • Do not artificially cool your epoxy to try to get a longer pot life. It will just make it too thick, hard to mix, and hard to wet out your glass. You’ll spend more time trying to do these things and lose any advantage you might have tried to get.
  • Never let a large mass of epoxy (> 100g) cure in a cup unattended. Depending on your epoxy, this could generate a great deal of heat, melt the cup, smoke, or even burn. Smoke from epoxy is toxic and you should get it outside ASAP, and get yourself to fresh air. Do not breath it.
  • Always test new epoxy. I once got a batch from a reputable manufacturer which was bad. When mixed it turned white, took forever to cure, bubbled, and was brittle when cured. They replaced it, of course, but I would have been sad if I’d found out during a layup.
  • Mix a 100g test sample, apply it to a few “coupons” of fiberglass, and press them with proper heat. Ensure the coupons demonstrate the cured properties you expect: flexible, clear, strong, etc. Make sure a portion of it cures at room temperature as you would expect. Label the cans of each batch, and label the coupons, and keep them.
  • Use epoxy specifically formulated for snowboards and skis, not a brittle epoxy designed for boats.
  • Explain using pigment to learn to mix well. A very little bit of pigment mixed with the hardener only will show swirls and voids where you have unmixed resin.
  • How much to mix: see the section on fiber fractions and weights.
  • Epoxy and heated cures. Post cures. Heat is always better.
  • Get the interview with Roy post back on Skibuilders, and link to it from here. Heck, maybe copy it here if Kam is cool with that. Super-valuable and should never be lost. I have it in a forum full backup in my own archive just in case.
Last modified Saturday March 23, 2019, at 19:49:47 UTC


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