: What's the best way to completely clean the surface
: before applying the first varnish coat? I have mineral spirits, but some
: resources suggest against that while others say it's fine. I'll be using
: Z-Spar Flagship varnish.

I've used Flagship on a kayak for a customer a few years ago. It has a rather dark hue but is really nice stuff. To answer this part of the question, go to the Pettit (Z-Spar) website and download the application PDF.
http://www.pettitpaint.com/fileshare/product_pds/28720106.pdf
On the first page is a paragraph of general surface prep. "
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