If you can dent the epoxy with your fingernail, you can recoat without sanding.

: The blemish didn't come from the water on the epoxy. By the time I sanded it
: was pretty hard and not tacky at all. The white blemish came from sanding
: a hardened puddle of epoxy. I used a slightly damp rag to wipe the dust
: off from sanding before I put the glass on. I thought the blemish would go
: away when I put fresh epoxy on it but it didn't

: I'm facing the same problem again. Its been more the 24 hours since I put the
: glass on and I guess I'll have to sand before I start fill coating. At
: what point does the chemical bond go away and mechanical bond needed?