A similar technique is used to deal with the "orange peel" that develops
when first spraying Prestec. See Kochanski's article at the SRA site. He
uses thinned blue dope. Also helpful: I use large carpenter's lead pencil
to mark up the border area between old and new gel coat. When the pencil
mark disappears - it's time to STOP sanding.

Roy A. Bourgeois