Do you mean stuff to put in epoxy, or stuff to use instead of epoxy?

Stuff to put in epoxy- a friend of mine has a lot of experience building RC planes. He had a kayak repair to do and he didn't want to wait for some silica, so he used baking soda because that's what he used for his RC stuff.

Substitute for epoxy- can't think of a good one, really, but I can say that when I worked in a professional cabinet shop we would use corn starch with PVA glues to make a filler if we had uneven glue lines that for some reason could not be fixed. It's good for faulty glue lines, but I don't know if I'd use it for filleting.

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