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Re: Urethane and Polyurethanes *PIC*

Bill Tindall, E.Tn.
somebody put this in the Articles so I don't have to keep repeating it.......

"Urethane" is the name for the chemical linkage used to hook together small molecules to make bigger ones. "Poly(urethane)" is a polymer(resin) made by hooking together small molecules to make a polymer with this linkage. As it pertains to varnish this name reveals that some or all of the polymer in the formulation is a polyurethane, and/or the finish is crosslinked with urethane linkages.

Confused? The name urethane on the can tells us nothing about what got linked together or how much of the finish components are polyurethane resin. However, in general polyurethane varnishes are tougher and harder than previous varnish formulations. All the other varnish properties as well as these two vary depending on what got linked, how much , etc. Bottom line, the name offers no reliable predictive properties.

"Years ago I saw examples of polyurethane finishes and they were a rather thick film that felt like plastic" Such a result is a result of varnish, any varnish, application and has nothing to do with the chemicals in the can. Apply it thick and it will look thick. When urethane resins began showing up in consumer varnish "experts" stuck in their ways disparaged these new products. Followers repeated the claims and these varnish products acquired a reputation that only people that didn't know better would use them.

Some example:

One of the top Period furniture makers displayed a pie crust table at a SAPFM meeting. The audience asked what it was finished with, anticipating the answer to be French Polish, to confirm their prejudices. Nope. He replied that this was a table that got used regularly and it was finished with durable poly(urethane). Nobody could tell the difference.

A friend sells jewelry boxes that you may have seen in Southern Highland craft shops. They go for $500. You have never seen a better finish on wood. It's poly(urethane).

And finally, the picture shows our used daily soft maple dining table, stained cherry, and finished with poly(urethane) about 40 years ago.

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