guide coat is good for taking away orange peel or a spar bump, but pencil makes a much smaller mess -AND- if he uses guide coat, he'll have black lines on his wing forever, since it will wick down into any remaining crazing (unless he plans on sanding the crazing away entirely, but that may also mean sanding the gelcoat away entirely, depending on how severe it is).

The technique i am describing is only finish sanding. the pencil is there to show what section to sand in, and the chord-wise pencil line lets you know if you've removed enough material/ not missed spots as you sand spannwise..

-ND

On Saturday, March 26, 2016 at 6:51:18 AM UTC-4, wrote:
Rather than pencil marks I recommend 3M dry guide coat. Even when wet sanding.

Lane