Filling weave/final coats of epoxy

 Hi there, We're currently somewhere between filling the weave and doing the final coats of epoxy on our tenderly build, and are experiencing some difficulties with our epoxy. We're trying to get the boat done for my pat leave at the end of may, and are spending nearly every weekend on the boat trying to finish the hull, but i'm starting to feel like we're just spinning our wheels. The problem is that the epoxy is setting up not quite right. It's got a very mild tackiness the first time you run your hand over it after setting for about a week, which then disappears. But when you sand it there are areas that don't come off as dust, but rather in little rolls that either fall off or quickly clot the sandpaper. Some of these spots then stay white after reapplication of epoxy. It's starting to get a bit frustrating. After doing some cursory searching i think it could be one or a combination of the following things: 1) too cold, we're working in an uninsulated, unheated garage and it's been somewhere between 5- 10 °C. We've been using a combination of heatlamps, incandescent bulbs+plastic sheeting to take the edge off of this problem, i'm not sure how effective this has been. 2) epoxy too old. I feel a bit foolish admitting this but, we originally bought the epoxy when we started the project 3 years ago, we've had 2 kids since then and the project has been sidelined a lot in that time. Not going to use that epoxy for the hull anymore. Maybe for the fairing of the floatation blocks. 3) not mixing properly. We've always proportioned with a digital scale and have worked within a tolerance for error < 1g. My only concern is not manually stirring thoroughly enough. We've also recently been reusing a mixing container which in retrospect seems like a mistake. Ok i know this was quite long winded, but any help would be greatly appreciated on how we should best proceed. Are we wasting time and resources trying to finish this step while the weather is still cold?

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RE: Filling weave/final coats of epoxy

It sounds like the temperature to me. 10 degrees Celsius (50 for the Fahrenheiters) is below the minimum curing temperature and even with heatlamps would take a long time (weeks) to fully cure. 

3 year old epoxy is still good unless you've either actively abused it or it has frozen at some point. In the second case it would have crystals in the resin. Those can be removed by soaking the resin bottle in hot water and the epoxy will be rejuvenated.

It doesn't sound like a mix problem to me. Your mix procedure was not the best in the world, but it would have caused different problems than you're seeing.

Good luck,


RE: Filling weave/final coats of epoxy

Hi Lona, 

everything laszlo said....i would highlight a couple things when you are exploring low temperature application.

  • keep your epoxy inside and at a comfortable temperature in the mid to high 70s',   this will keep it thin and viscous.   when the epoxy itself get gets very hard to mix properly.
  • you can do a test of a small batch of warm epoxy mixed properly to confirm if your epoxy is good.  if that small batch is good, then you can do another test where you let it cure in the garage with the lamps heater.  that will then confirm that the local heat is enough. 
  • when i work in my unheated garage and use lamps and tarps to hold the heat close to the boat, i use refrigerator magnets to make sure i know the temperature where the epoxy is at.
  • you will need to scrape off all the old/bad epoxy before you restart.  good epoxy over bad will not solve anything. its a pain....but needs to be done.  a scraper , followed by sanpaper should do the job.

hope that helps.


RE: Filling weave/final coats of epoxy

   just one other point i wanted to make....based on past mistakes.  i would actually highlight that this could be a mixing problem...right proportions....but you did not stir it well enought.   if the proportions are right and it is stirred well enought, it may take longer....but it will cure.  if its not mixed right...or there is some other chemical will never cure properly.

one final experiment is to 'bake' the epoxy you already have out there to see if you can get it to fully cure.  the idea is basically wrap the boat/piece in plastic/create a tent over the piece where you can then really drive the temperature up....into the high 80s, low 90s for 8 hours...if it does not cure after have a mix (not stirred well enought or not the right proportions) or epoxy chemistry problem (adulterated epoxy or chemical contamination on the surface you are applying it to).


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