A friend is building a Arctic Tern and is at the point of sanding before varnishing.

The question is, when is he done sanding? He's done 150 grit (dry) sanding (sanding disks on a random orbital sander) and it looks good, feels smooth. You can't see any "shiny" spots of epoxy.

Don't want to oversand, so how can he tell if he's ready to move on to varnishing?

Thanks for any input,

Tom