Maybe you missed the fact that the doors were exterior doors. Water based poly does not have any UV protectent in it. You must have UV protectent.
Another reason to use a SPAR Poly is because it does not dry as hard as regular poly therefore it adapts to the movement of the wood with seasonal changes.
I would not use water based poly on an exterior door. I have been told that spar is the best choice but it won't last forever. The Helmsman that he used is a spar poly.
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