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System Three

Marine Spar Urethane Varnish

Item #847115 Model 1855S16
Regular price $54.99
Sale price $54.99 Regular price $54.99
System Three® Spar Varnish is a urethane enhanced film finish formulated to protect against the harshest salt water and marine environments, as we. . . View More Details

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System Three® Spar Varnish is a urethane enhanced film finish formulated to protect against the harshest salt water and marine environments, as well as provide protection for your outdoor projects. It contains UV absorbers and other additives that help it combat the worst that nature has to offer. System Three Spar Varnish, like all outdoor film finishes, is more elastic and a bit softer to enable it to move with the wood as it expands and contracts with the seasons. It’s a good finish for outdoor furniture and projects in general but like all outdoor finishes, it could use a little help – a good base underneath to keep it looking good longer. We recommend sealing the wood underneath with a good waterproofing sealer.

The number one enemy of an outdoor film finish is moisture that gets into the wood and underneath the finish. Moisture makes its way into the wood via the wood actually breathing (a result of not sealing the wood off from ambient moisture in the air), as well as through micro fissures in the topcoat caused by temperature extremes and UV radiation. So, if you’re contemplating a film finish for your outdoor furniture – consider using a good sealer underneath. A sealer will combat this “breathing” the wood does and be a barrier to prevent moisture from expanding underneath the topcoat, even if it manages to get through the micro fissures. The bonus for this hard work is your finish will look good well beyond what you might otherwise expect…but not forever.

Start with a good sealer such as System Three Clear Coat. If it’s going to be outside all the time all year long and even if it’s not, System Three recommends encapsulating the wood with System Three Clear Coat prior to assembly. This will effectively stop the wood from breathing and provide an excellent base for the topcoat to adhere to plus it will stop moisture from spreading underneath the finish through micro fissures. Be advised that even if you follow all these recommendations, you will still need to take steps to care for your project in the off-season and to eventually apply a new coat or two of finish or remove the old finish down to the Clear Coat and recoat the piece. However, following our suggestions will keep your Adirondack chair or other outdoor project looking good longer, and it will be easier to recoat when necessary.


  • Designed for marine and exterior wood surfaces
  • Offers excellent protection from salt air and water
  • Contains ultraviolet light absorbers that protect finish from exposure to sunlight
  • Formulated to cure properly over System Three epoxy products
  • Does not require sanding between coats when additional coats are applied within 24 hours
  • VOC compliant


  • Type: Oil-modified urethane polymer
  • Size: Quart
  • Sheen: Gloss
  • Color: Very light amber
  • Interior/Exterior Use: designed for exterior use
  • Recommended Use: Directed at, but not limited to, the finishing and coating of wood
  • Application Method: brush, roll, spray
  • Coats: varies per project (see PDF System Three Clear Finishing of Outdoor Wood)
  • Coverage: 100-125 sq.ft.
  • Minimum Application Temperature: 50°F
  • Maximum Application Temperature: 95°F
  • Ideal Drying Conditions: 77° F and 50% humidity
  • Dry Time - Tack Free: 4-6 hours
  • Dry Time - Dust Free: 8-12
  • Dry Time - Recoat: 12-24 hours
  • Dry Time - Complete Cure: 14 days
  • Clean-Up: mineral spirits or lacquer thinner
  • Material VOC (g/L) 440-450 g/L

What's Included:

  • (1) Marine Spar Urethane Varnish - Gloss - Quart


  • Please see the PDF from System Three (link on this page) for more information on finishing outdoor wood.