Anytime you let fresh epoxy set there is amin blush working it's way to the surface. It may not appear on top for 18,24,36,48 hrs., but it's coming. If you try to laminate or coat over it you will get a bad bond.
Why even worry about such an occurance? The best way to outrun amin blush is to lay the coats on as close together as is practical. Epoxy hardens by a chemical reaction. It's not like paint that hardens by solvent evaporation. Once epoxy starts to kick it will do so whether it's on top or three layers down.
Remember that old familiar refrain, "wet-on-wet", "wet-on-wet". You can forget about sanding, washing with water, washing with ammonia, wiping with solvent, purification rituals, incantations or the power of oom.
The whole idea of fill coats is to bury the 'glass deeply enough that if the finished surface needs a sandpaper touch-up it can be done with out digging into the glass layers.
Fear not. Just lay the goo on wet-on-wet.
Charlie

: Seems like it's standard practice to sand the glassed exterior before
: applying a fill coat. Why sand? I understand it is probably necessary to
: remove some excess epoxy, BUT if one were extremely careful to squeegee it
: off while wet or scrape it while green, would it still be necessary to
: sand before doing the fill coat?

: I thought the idea was to avoid sanding into the glass, and if the exterior
: weave texture is already evident and uniform, wouldn't it be difficult to
: avoid sanding into the glass?

: (Yes, I'm going to have to sand anyway, where the edges of double layers at
: the stern and bow are obvious. The rest came out really nice and
: bubble-free, thanks to using foam rollers followed by squeegeeing. Gotta
: glass the deck next, and then it'll look like a kayak :-) )