Spar vs. Traditional Polyurethane Varnishes Wood Finishing Tip
By Alan Noel
Professional Wood Finisher
I first started using polyurethane based varnishes way back in
college on primitive reproductions that Willard and Otis (yes their real names!)
would build out of old tobacco barn logs. They would fume the
wood in a tent for bugs and then slice the logs up into lumber
for their reproductions. I would then oil the pieces with just
"plain old varnish" the way they taught me to do...thin it with mineral
spirits 50/50 and "just slop it on" all over. Then wait a few minutes and
wipe off the excess. After two slops, bowling alley wax was applied
with fine steel wool for final sheen. This was a very nice looking, durable finish and
one that was fool proof and simple to apply. I still have a pine shelf over my desk that
I made and finished this way.
Fast forward to the early eighties I was getting a lot of requests for
exterior finishes on outdoor furniture and exterior doors. Having
never done this type of work I asked a friend for his advice and he said to use
"spar polyurethane varnish" and not regular polyurethane since spar
was designed specifically for exterior use but could also be used for interior use, while regular polyurethane varnish was for interior use only.
The reason for this, he said, was because spar was a "long oil varnish"
containing slow drying oils which in turn would stay soft for an extended
period of time and therefore hold up to the elements depending on how
much the surfaces were exposed to the weather and direct sunlight. Being in
the south and having done a few exterior doors, the sun is definitely the deciding factor
for me, not to mention the amount of humidity we have here year round. If in
direct sunlight I've always recommended painting the woodwork or be prepared to
pay me 2-3 times a year! As for using spar for interior use, the only drawback is the
much longer curing time and off gassing of the thinner. Otherwise, spar is fine for
As always, make sure you have good air movement in the finishing area,
especially when applying any oil type finish. And don't forget to always practice on scrap first.
Alan can be reached directly via email c/o Alan Noel Furniture Refinishing at email@example.com. You can also visit Alan's website by CLICKING HERE.
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