I would use water but the helmet isn't 100% glassed yet. Can't have the mat board soak up any water, that'd be bad m'kay
I'm dry sanding for now with 320 grit, then primer.
This is just regular primer [spray] for now. I might do a final coat with high solids automotive primer to hide any tiny imperfections left.
The primer will be sanded with 1000 grit before paint and clear.
Also, I wouldn't even think about using any power sanders on something like this. Its all done by hand.
Here's a quick tip on making annoying sections to look nice and smooth.
I figured this might help quite a few people having problems with this kind of detail work.
I'll be posting a second one soon on how to make the squarish recessed areas on each side of the mouth guard area..