You should fair your hull before you fiberglass. If you fair your hull after you lay on the fiberglass, it will be pretty difficult to avoid sanding into the fiberglass on any high spots. Even if you don't do that, you'll leave a lot of resin in the low spots, which will add unnecessary weight to your hull. I hope that answers your question.

Hi careybob, 

Thanks for the response. I probably wasn't very clear.  I am trying to do something Lazlo has done with his Wood duck where he filled the weave on his hull with microballons rather than just epoxy since he was going to use graphite anyway.  

I'm just wondering if in that situation since i'm going to paint the sides as well that it doesn't matter if I go ahead and fiberglass the deck before doing all the weave filling with microballons on the sides and hull.  I was thinking that would help with making the deck and hull/side fiberglass line easier to sand and smooth.  

thoughts? 

   I've done a handful of boats with putty on the hull glass, and straight resin on the decks. You can do major fairing before glass if you want to- things like splice lumps or bow transitions. Pre-glass, I'm more comfortable using lighter fillers too, like West's "Micro-Light" or other talc-based filler. After glass, I limit myself to phenolic balloons which make a harder finish for the paint.

I like to get at least my first fill coat applied while the glass is still green, since any blush will be difficult to remove from the raw weave. After the first fill coat, the epoxy is smooth enough that I can scotchbrite it with water after it fully cures.

  Justin,

Sounds good to me. I can't think of any reason why it would not work the way you described it. If you enlarge my pictures and look carefully, you'll see that the deck was glassed before any of the weave was filled. In fact, I always leave filling and fairing as the very last step before starting the finishing. I find that I use less epoxy that way (and I haven't had a boat come apart yet).

Have fun,

Laszlo

   Great!   Thanks everyone for the input!

Justin