I get Minwax polyurethane and it is oil based, indoor use. But I have some projects that will be used outside, couldn't I use the stuff I have without having to buy spar urethane? I am thinking it will work because it is oil-based. Water wouldn't be able to remove it very easily. So why is it indoor use only?

1 Answer 1


regular PU is not well-suited to the outdoors because:

  1. it has no UV degradation inhibitors in it, so eventually the sun will eat it.

  2. it is fairly rigid/brittle. seasonal movement will cause it to crumble.

spar PU/varnish has UV inhibitors in it and it is more flexible than regular PU to prevent exactly those two types of failure.

  • Good to know. I figured there was something. Thank you for the answer
    – Ljk2000
    Feb 8, 2018 at 17:37

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