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"varnish" vs. "polyurethane"

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Forum topic by Mainiac Matt posted 02-28-2012 06:39 PM 1621 views 0 times favorited 2 replies Add to Favorites Watch
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Mainiac Matt

5989 posts in 1789 days


02-28-2012 06:39 PM

sorry for the novice question…..

but these terms get tossed around and I’m not sure what the distinction is.

Are “varnish” and oil based “polyurethane” really the same thing?

and ….

does BLO go bad?

I’ve got about a gallon and a half that have been on the shelf in my basement for 13 years…. and may finally have use for it.

-- Pine is fine, but Oak's no joke!


2 replies so far

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Loren

8295 posts in 3108 days


#1 posted 02-28-2012 06:46 PM

The application of poly is similar to the older styles of
alkyd varnishes that preceded poly. Oil-based poly may
be mixed with spar varnish and other oil varnishes.

Varnishes cure by oxidation while lacquers and shellac
cure by evaporation of their solvents. Because of this
varnishes are trickier to repair and dry slowly in comparison
but they have many other virtues than compensate in
some applications, such as toughness and flexibility.

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Manitario

2397 posts in 2344 days


#2 posted 02-28-2012 07:05 PM

My understanding is that Varnish= oil +resin +heat. The oil can be eg. linseed, tung, soybean, etc. The resin part can be phenolic, alkyd or polyurethane. The stuff you see sold eg. “polyurethane” or wipe-on poly is a varnish with polyurethane as the resin.

-- Sometimes the creative process requires foul language. -- Charles Neil

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