Hi Everyone:
           I am skinning an engine part and the first several coats went well, and I made sure to follow the rules about sanding down the high spots after a few coats of resin, scotchpading the low spots for good adhesion of the new layer, etc.  When I thought I was done, I was starting my polishing sands with a 400/800/1000,etc, but after the 400 grit, these weird white "worms" could be seen and spots all over.  I had not seen this before, but I had used my heat gun to remove bubbles, so I wouldn't think they are air bubbles.  Is this a bad mix on my end?  Maybe I didn't mix the resin/hardener enough?  BTW, I am using a 3:1 epoxy resin and hardener from US Composites. 
Any help in understanding potential causes so I don't repeat would be appreciated.

For now, I figure I will have to sand the blemishes down and do another few coats.  Bummer...

Thanks!