Rubbing out Spar Varnish

Like interior varnishes, spar varnish rubs and buffs to a gloss — but there are some things to keep in mind. December 1, 2005

Question
I'm finishing an exterior door for some clients and recommended a high quality marine spar varnish. Does anybody know if spar has the same rubbing out qualities as regular interior varnish? Is there anything special I should know?

Forum Responses
(Finishing Forum)
From contributor R:
I'm not a professional finisher, but have done quite a bit of work on boats. Perhaps these comments will hold you until a pro weighs in.

As far as I know, you cannot rub out a spar varnish. Spar varnishes are tough, but not hard. Their elasticity is what allows them to move with the wood in the harsh outside environments. The counter to this is that because they are not hard, you can't rub them out.

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From contributor G:
I've never tried it myself, so I can't speak from experience. If you want something you can rub out, I would recommend contacting your Chemcraft rep and ask about D-Dur.

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From contributor T:
I have restored several wooden boats with marine (spar) varnish on mahogany. While it is true that spar varnishes are long oil (vs. short oil) and thus remain somewhat flexible, they can reliably be rubbed out. I would use 400 then 600 on a foam auto body pad, followed by 1000 grit paper.

Then I would use 3M Imperial Microfinshing compound followed by Finesse-It III both on buffing pads. Incidentally, you should wait a long time prior to rubbing out spar finishes as they continue to dry for weeks leading to reverse sanding scratches after rub-out as the finish continues to shrink.