I'll second (actually third) Hank's recommendation. I'm now a disciple of UH and Church of the Holy Pinhole.

Our club tends to wait until the existing gelcoat approximates the look of a dessicated mud flat before we start a refinish. So, almost all the old gelcoat ends up coming off, which results in PINHOLE HELL. After following Hanks advice on last year's LS4 project, I could count the number of pinholes with hands and toes, as opposed to prior jobs where we spent several cycles trying to spray our way out. This year's Grob Fuselage had a couple of pinhole fields only because I was sloppy on the prep work.

In terms of prep, I supplement the air blowing with a wipe down using a lint-free rag and either Prep All or Acetone.

I'll add that a really soft rubber scraper used to squeegee the Polyprimer into really bad pinhole fields seems to work even better than the roller if you are careful. We sometime roll then go over with the scraper working back and forth a few times.

P3

On Tuesday, April 4, 2017 at 11:56:12 AM UTC-4, wrote:
On Tuesday, April 4, 2017 at 10:53:46 AM UTC-4, wrote:
Go with Hanks advice. He guided me in the refinish of CF and it turned out great. I was constantly advised by spectators as to how I "should do it". One guy grabbed a gear foot and promptly sanded through to the foam core.. From then on I didn't mind being rude to the next neighbor with the "better idea". In short, don't make it complicated.

Simtec also has a filler if you are using their products.

Lane

Simtec 2081 does not sand anywhere as well as Polyprimer. JJ put me on to Polyprimer.
UH