: Dave,

: Have you faired and sanded the outside of the deck yet? If you haven't, keep
: in mind that some of the gaps might show up on the outside as well. If you
: haven't faired and sanded the outside yet, you might want to hold off on
: the filling.

: Pedro Almeida

Pedro,

I did an initial sand with a random orbit sander with 60 grit. I think, based on your advice, I will do more with my fairing board and 80 grit. As far as my choice of underdeck filler, I've decided to play it safe and use a microballoon-based epoxy filler mix (west system 407). As for the few small cracks on the outside (maybe more after additional sanding) I've been experimenting with Elmers (water-based) red oak wood fill and it looks pretty good.

Thanks for the advice everyone. This forum is great!!!

Dave