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Urethane vs Polyurethane

Robin Thompson

Robin Thompson

Joined
May 19, 2011
Messages
92
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18
Location
Sarnia, Ontario
Is there a difference? I have been applying a three part finish to some turnings for several years. Equal parts of Tung Oil, Linseed Oil and Urethane. I needed to make a new batch and realized I have no Urethane left. Off to the hardware store only to be told Urethane was no longer available. "But, we have Polyurethane and that has replaced Urethane". HHMMM! Is this true. I can't seem to find Urethane anywhere.
 
What's in a name? The witches said it first. "Macbeth, you're a Thane!" Urethane was ethyl carbamate first, but polyurethane is not the polymerized version. Confusing? Means that what you got as "urethane" wasn't really the same stuff that is regulated in fermented beverages, but a resin which was composed of larger molecules containing carbamate groups.

A lot of choices out there in finishes with (poly)urethane, oil or water based. If you still have your old container, check out the % of solids and resin, then match it and your solvent so you don't have to discard any tricks you may have developed with your former finish. You are, of course, obliged to divulge them here in payment for the explanation.

So there you are. Brontosaurus becomes Apatosaurus to clean up the family tree and our friend the roughing gouge is now referred to by the squeamish as a spindle roughing gouge because they don't know how to employ it properly. Life's like that.
 
No secrets divulged herein

Sorry, there just are no secrets involved. This finish, at least the original one with the urethane, is mixed as previously indicated, applied liberally and left for about 5 minutes before rubbing off excess finish. I apply 3 or 4 coats like this, obviously letting each coat thoroughly dry, then sand to 400. I follow this procedure again applying 3 or 4 coats. Then I sand to 1500, get rid of any residue and apply a light coat. That is it. This is not a finish I would use if I were in any rush to complete a project nor do I use it on anything but furniture or turnings not going anywhere near food. It dries hard and holds up well. Unless I drop the turning from the upper deck.

Thanks for the reply guys. Both are good answers.

Rob
 
not going anywhere near food. It dries hard and holds up well.

Robin, glad you found an answer to your question. Just for the record, once dry, you finish mixture and any one else's, if food safe.

Bob Flexner has an explanation in the AAW Journal of Spring 2008, available on the mothership by clicking on the logo in the upper left corner.

All the best, Tom, in Douglasville, using Poly on bowls without hesitation.
 
Robin
Try General finishes Armer Seal it's oil and Urethane. I use it just as is and love it.:) You can flood, let set,wipe then let dry and buff. I apply with rag and rub it in to almost dry let finish dry and buff. The oil helps the Urethane sink into the wood before it sets-up very hard totally repairable really nice finish. Comes in gloss, semi-glass and satin.
 
Minwax still makes spar urethane. "Spar" formula finishes are usually exterior rated, and a bit softer and more flexible than other urethane/polyurethane finishes. Because of this, they will adhere better and have less tendency to crack due to wood size changes or temperature changes. They may scratch more easily, but they also usually buff up a little quicker. Drying time is usually longer.
 
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