Here's a question for y'all. I'm currently sanding the chalky old gel coat off and old model glass canoe. I've got the worst of the decayed gel coat off...revealed what's left of the undamaged gel coat. Can I lay epoxy over the remaining gel coat and expect it to stick or must I apply New gel coat?

Robert:
Clean (no wax or silicones), sanded gel coat makes a great base for epoxy. I haven't coated large areas of gelcoat with epoxy but I've done a lot of filling and repairs and mods on gelcoat in the last few years, and had no adhesion problems.
I don't know if your canoe has a lot of areas where the gelcoat is completely missing, but it might be easier to just sand and polish the remaining gelcoat (after doing some necessary scratch fills?), rather than coat with epoxy.
Another option is to patch/repair/fair with epoxy and then paint with a good 2-part primer and paint system. That's what I do when I alter (gelcoat) kayak decks.
Can you give a few more details (and pics?) of your project?