Polyurethane drying in can

I remember reading somewhere that you could prevent polyurethane from drying in the can, especially when the can is less than half full, by removing the oxygen and replacing it with another gas. Unfortunately, I can't remember where that was.
Does anyone know what gas would work?
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One method is to store the can upside down, so air cannot enter around the edges of the lid. Any deteriorating reaction is limited to the top layer of coating, which becomes the bottom layer when you turn the can right side up.
--
Don Phillipson
Carlsbad Springs
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On 9/26/2012 4:31 PM, Oren wrote:

That's what works but it is not air getting in but solvent getting out.
If it were uncured polyurethane, air does not cure it but moisture in the air does.
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On Wed, 26 Sep 2012 18:06:32 -0400, Frank

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On 9/26/12 2:23 PM, Gordon Shumway wrote:

Try blowing a big fart into the open can then quickly slam the lid on.
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Yeah, right. What happens when you open the can later? :-(
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The gas used is heaver than oxygen, or more correctly, atmosphere. Simply injecting the gas into the can is all that is needed to displace the oxygen. Once the lid is replaced you're good for who knows how long.
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Gordon:
Any gas other than oxygen will work.
The problem is that there aren't too many compressed gasses you can buy in small quantities.
What I use is butane:
[image:
http://cdn102.iofferphoto.com/img3/item/200/423/994/ronson-lighter-refill-butane-fuel-fluid-42grm-1-48oz-b04a.jpg ]
Just buy a short piece of brass or aluminum tubing from any hobby shop, or use a piece of larger plastic tubing (from expanding foam caulk, say), and slip it over the dispenser nozzle of the butane cannister. Now, when you're ready to seal your can, put the lid on the can but don't pound it down yet.
Lift one side of the lid and slip your butane dispensing tube under the lid. Pull the butane dispensing tube backward toward the butane canister, and butane will flow through the tube into the can.
Butane is heavier than air, and will gravity segregate to the bottom of the empty space in the can, forming a physical barrier between the liquid and any air remaining in the can, and that's just as good as not having any air in the can.
But, what's important and that most people don't realize is the oil based coatings (including alkyd based polyurethanes) absorb oxygen from the air all the time the lid is off the can. So, if you start painting at 2:00 PM, and seal up the can at 4:00 PM, it's a waste of time to put butane in the can when sealing it up. That's because the oil based coating was absorbing oxygen for two hours, so there's plenty of oxygen absorbed into the surface of the oil based coating to form a film while in storage.
What you should do instead is: A) remove any dried film on the surface of your can of oil based coating, and stir it to ensure that the solids are uniformly dispersed in the liquid.
B) pour off as much oil based coating as you think you'll need (or a little more) into an old soup can, disposable cup, or whatever.
C) immediately inject butane into the can of remaining oil based coating as described above, pull out the butane dispensing tube and let the lid sit on top of the can while the butane inside warms up and expands (so you don't have any serious pressure inside the can).
D) Now pound the lid down on the can to seal it. E) Now go and paint from the soup can or disposable cup. Don't pour any unused paint back into the can if it's been exposed to air for over an hour. Better to store that in a smaller container (like a glass or plastic jar) so that it doesn't absorb significantly more air, and let the dried film form in that smaller container. (you can buy pint and half pint miniature paint cans at any place in your city listed under "Containers"). Better to put a thicker coat of poly on for better protection of the substrate than to have to throw more dried poly film into the garbage.
REMEMBER: The butane is a liquid inside the butane cannister. If you hold that butane cannister at an upside down angle when injecting butane, you'll be injecting liquid butane into the can. If you then push the lid down onto the can so that the resulting liquid butane transforms into a gas inside the sealed can, it'll build up considerable pressure. Sometimes the lid will fly off shortly after sealing the can, other times it'll fly off when you next go to open the can. So, after injecting the butane, it's best to just let the lid sit loosely on top of the can to allow any excess butane to leak out of the can before pounding the lid down. Butane gas is heavier than air, so as the butane liquid vapourizes into butane gas, it'll push the residual air out of the can.
Hope this helps.
--
nestork


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On Wed, 26 Sep 2012 22:53:22 +0000, nestork

Thanks for all the info!
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Gordon Shumway wrote:

Exhale into the can. Three times. Slap on the lid.
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PROPANE
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