wrote
I have just finished sanding and staining the interior of an exterior
door. Should I use interior or exterior polyeurethane on it? I'd
prefer to use the interior variety because I happen to have it, but I'm
not sure if I should use that or the exterior version, presumably since
this is an exterior door and even the inside of the door will be
subject to more hot/cold swings than an interior door would. Other
than that I can't think of any compelling reason to use the exterior
variety.

I have 5 doors that lead to the exterior and were protected with exterior
spar varnish (marine grade) on the exterior and interior poly on the
interior.
The finish was applied about ten years ago and is still in very good
condition. I have one exterior door on a storeroom that was finished with
the same latex trim paint as the house trim; applied less than a year ago. I
can tell it will not last.

Max
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