This is almost always caused by an off ratio of resin to hardener. Forgetting how many pumps of part A, and adding too much of part B, or vice versa. Most mixes will eventually cure if the ratio is a little off, like within 20% of spec, but missing a pump stroke can easily exceed that. Once you're out of the forgiveness zone, the mix just will not cure. (Some optimistically overcoat a soft patch with fresh mix, hoping to provide/dilute/offset the missing component by adding it with the next coat, and this may occasionally work, but it scares me to bury an uncured patch this way.)

So, acetone and a couple of cloth rags and some tough gloves are in order. Not latex/nitrile exam gloves, but tough kitchen gloves here. Thoroughly wet a bit of rag and just start scrubbing, putty knifing the loose stuff, and acetone scrubbing some more. It won't be fun, but it sounds like you didn't use this batch to wet out any glass, so that'll make things LOTS easier, and neater.

North East Sailor,

I'm in 100% agreement with nemochad.  Had the same problem when we built my Peeler Skiff---one small batch of resin was somehow mixed improperly and never really cured.  At least your problem epoxy is on top of the glass.

Acetone and lots of elbow grease removed the gummy stuff with no permanent harm done.  We found that those green plastic scouring pads helped too.

Cheers,

Dick

   Thanks for the responses.  I was able to clean up the second and third planks and I still have more work to do on the bottom panel and first plank.  It's good to be back on track.