Hi,
You can put on as many layers as you want at one time as long as you can wet them out properly. Putting them on one at a time means you run into potential problems with blush. However, if something goes wrong you haven't messed up so much if you do one layer at a time. If you do do multiple layers at a time you will need a bubble roller to get rid of bubbles and to stop the glass from floating.
JohnK

: sorry to be a pain, but I've got no fiberglass experience, I've been putting
: on a layer and letting it dry and then putting on another, is that right
: or do you lay it up wet-on-wet? Tired of glassing, want to go surfing! Why
: isn't there a class I can go take to learn how to build a glass boat!