The tack cloth should not cause a problem with ZSpar. I'm not sure what would. It is possible there was something on your hands. Try to avoid touching the boat with bare hands after sanding and before varnishing.

Stick the boat out in the sun and see if you can get the spots to harden. Then sand those spots well before revarnishing.

> I have just put the 3rd coat of varnish on my Guillemot Coastal and found
> there are a few spots on the deck where something strange happend to the
> varnish. The majority of the boat dried to a high gloss as I expected,
> however, there are a few spots where the finish is dull and flat. The
> varnish also remained tacky on these spots for a couple of days. It seems
> to have dried now. The first two coats went on fine. I'm using Z-Spar
> Captains varnish.

> My procedure has been to wet sand with 320 grit paper, wipe down with a
> sponge and damp cloth, and then wipe with a tack cloth.

> What could have contaminated the deck and caused the varnish to do this,
> or is it the varnish? The only thing I can think of is that I may have
> wiped these spots harder with the tack cloth and left some sort of
> residue. Anybody have any ideas?

> What should I do about it? Just try another coat? Remove the varnish with
> a solvent and try again (Ugh!)?

> Thanks.