I'd use a putty knife and get as much of it off that way as possible first, then a cabinet scraper to take it down to solid epoxy or wood, whichever comes first. Then I'd sand with sacrificial paper, between 80 and 100 grit, changing frequently until the new pieces of paper stopped gumming up.

Once that's done I'd wipe everything down with denatured (not isopropyl) alcohol, let it dry and start the process of sanding it all back into shape and applying new epoxy.

I'd avoid acetone and other harsh chemicals because of the problems spills could cause with the good part of the boat.

Good luck,

Laszlo

Do what Laszlo says. It will certainly work.

Ignore me.

But in all honesty I took a different approach when this recently happened to me. I had a bit of tackiness around the interior edge of one hatch cover on the Shearwater Sport Sectional I am currently building. It wasn't a deep globby mess; just a thin sticky one. My assumption is that some small bit of resin did not get fully mixed with hardener. Hence the permanent stickiness.

I decided to ignore the problem and cover the area with another coat of epoxy. The best case scenario is that the new coat of epoxy has enough free molecules of hardener to activate the sticky resin and turn everything into perfectly hard epoxy. The worst case scenario is that this new coat of epoxy (which seems to have hardened quite nicely) eventually peals off, I have to sand off some still-sticky residue, and follow Laszlo's advice -- which should still work.

Call mine, the lazy man's approach. But I'd be tempted to try it on your thwarts. Those are not structural components so there is little downside to a failure. You can always take the thwarts down to bare wood if necessary.

Has anyone tried to rub sawdust into the uncured epoxy in an attempt to stabilize it and make it easier to remove?

   I know it's been awhile but I wanted to post a followup for anyone else who runs into this problem and to prevent others from making the same mistakes I did.

First of all, I ended up more or less using Laszlo's suggestion. I bought a bunch of cheap big-box grade 80-grit sanding discs and essentially ground my way through all the sticky resin down to bare wood, changing the discs every minute or so. Once I did this, I attempted to re-apply epoxy, but ran into the exact same problem with uncured resin, and had to go through the same process all over again.

In this moment of massive frustration, I realized the likely problem: Some weeks ago I had replaced the pump for the resin, but I didn't replace the pump for the hardener. As far as I could tell, they were the exact same (both from identical MAS pump kits), however I'm guessing over time some dried material built up in the hardener pump to throw the ratio off enough to cause problems.

I ordered a brand new set of epoxy pumps and replaced both. Epoxy now hardens exactly as expected. A hard lesson learned.