how long does oil based poly last after opening

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Forum topic by HokieMojo posted 02-26-2011 03:41 PM 1185 views 0 times favorited 5 replies Add to Favorites Watch
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2104 posts in 3755 days

02-26-2011 03:41 PM

i was going to apply some water based poly to a shop storage cabinet I built. I like the idea of being more environmentally friendly as well as having less fumes for me to breathe, but I did find a can of older poly (probably 5 yrs old). Will this stuff still work? I think the best of all solutions is to use up what I already have so I’m leaning this way. Any advice would be appreciated.

5 replies so far

View Sawkerf's profile


1730 posts in 3096 days

#1 posted 02-26-2011 04:06 PM

If it was tightly closed, it’s probably ok, but it may be a bit “thick” and a little darker than new. Thin with mineral spirits and use it up if there’s enough.

-- Adversity doesn't build reveals it.

View wseand's profile


2796 posts in 3069 days

#2 posted 02-26-2011 06:14 PM

Do a test on a scrap piece and see if it seems to set properly. If it cures properly than I would go ahead and use it.

View Scott Bryan's profile

Scott Bryan

27250 posts in 3849 days

#3 posted 02-26-2011 06:24 PM

The best thing to do is open the can and look at the material in the can. If the material is thick and has skimmed over then this is the result of the urethanes reacting with oxygen to polymerize (which is the reaction that we want to provide surface protection for the project). Once the product has polymerized it is an irreversible process that spreads rapidly throughout the can. In my opinion it is really not worth jeopardizing a project to save a few bucks and I toss it when it gets to this stage.

I have kept gallon containers of poly for several years and found on cans that have been opened fairly infrequently and are nearly full that they are still ok to use. But others that have had an appreciable amount taken out I have had skiim over in less than a year.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View EEngineer's profile


1103 posts in 3640 days

#4 posted 02-26-2011 06:24 PM

I have a can of oil based poly that is over 20 years old. I just used some of it to put a coat on an air compressor station I built last summer. In general, if there is enough in the can (mine was about 2/3 full), a skin will form over the poly and protect it from further degradation. Use a stir stick to peel off that skin, stir it up and use it.

In my experience, water-based poly does not last like this. Part of my problem, though, is that all of that is stored in the garage and it freezes every winter. Freeze it once, game over!

-- "Find out what you cannot do and then go do it!"

View HokieMojo's profile


2104 posts in 3755 days

#5 posted 02-27-2011 04:00 AM

Thanks guys. I was planning to apply a coat today, but now it looks like it will be next week at the earliest. That should give me some time for a test. I appreciate all the info!

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