Polyurethane question

[osage outlaw]

I might have asked this before, but I can't find the thread or remember the answer.  How long does polyurethane last?  I found a gallon of it in my wifes grandfathers garage while cleaning it out.  Judging by the can, it looks like it is pretty old.  Does it go bad?  Would it still be good enough to seal osage staves?

[sonny]

only good way to tell is to test it out on a scrap piece of wood.
polyurethane is simply a solution of some sort of thinner and some solids. seems the only way
it'd go bad is if the thinner dries out.........
 

[gstoneberg]

Is it still liquid?  In every case I've had poly get old, it was solid when I opened the can, or nearly so.  These days I only use spray-on.  It runs out or plugs up before it can get old.

George

[osage outlaw]

I haven't opened it yet.  I shook the can and it sounded like it was still liquid.  I guess if it is thick, it will just be a thicker layer of protection for the staves?

[Stretch]

only good way to tell is to test it out on a scrap piece of wood.
polyurethane is simply a solution of some sort of thinner and some solids. seems the only way
it'd go bad is if the thinner dries out.........

Polyurethane is a curing finish, not a simple solution.  The urethane molecules actually join together as the finish cures so that it's a different molecule once it's dry.  This is what makes it such a durable finish.  In the past, I've had polyurethane that wouldn't cure properly that was still liquid.  Like you said, the best thing to do is test it. 

[osage outlaw]

How do you know if it pasts the test or not?  I don't want to find out 6 months from now when all of my staves are checked.

[sonny]

Polyurethane is a curing finish, not a simple solution.  The urethane molecules actually join together as the finish cures so that it's a different molecule once it's dry.  This is what makes it such a durable finish.  In the past, I've had polyurethane that wouldn't cure properly that was still liquid.  Like you said, the best thing to do is test it.

I reckon that's what I get for assuming that polyurethane is simply a solution.
thanks for clearing that up!

[gstoneberg]

How do you know if it pasts the test or not?  I don't want to find out 6 months from now when all of my staves are checked.

That's why I buy new. 

[crooketarrow]

  Anything to slow down the lost of moister to stop checking. Checking comes from moisture leaveing to fast. You really don't have seal completely (better to) just slow down the moisture lose. Covering the stave just lets the moisture leave unfourmly. I've used just plain old spray paint on 100's of staves. Never had a checking problem.
  If it's not harden it will work.

[Stretch]

How do you know if it pasts the test or not?  I don't want to find out 6 months from now when all of my staves are checked.

It'll stay gummy. 

[Stretch]

Polyurethane is a curing finish, not a simple solution.  The urethane molecules actually join together as the finish cures so that it's a different molecule once it's dry.  This is what makes it such a durable finish.  In the past, I've had polyurethane that wouldn't cure properly that was still liquid.  Like you said, the best thing to do is test it.

 

I reckon that's what I get for assuming that polyurethane is simply a solution.
thanks for clearing that up!

  I was a chemist before I took up woodworking.  The furniture shop I trained in got most of it's business because it specialized in custom finishes.  Studying finishing from a chemistry point of view made things a lot easier for me to pick up.  Once a geek always a geek I guess.