Expiration date on unused finish?

10 year old poly? Trash it.

IMHO – It’s just not worth the trouble to test fate and use old finishes on any hand built project that you care how it looks when done.

Typically, If can has been opened the shelf life timer starts ticking. Most oxygen hardening varnishes or moisture curing poly finishes have a ~1 year shelf life after can is opened. If you amount left in can is less than half, then shelf life is usually less, maybe 3-6 months. After the finish shows thickening or sludge in can, attempts to use it can/will result in a poor finish. Could end up under cured and soft, or might have streaks in it when it dries. It’s not worth the trouble.

I will admit that if I open a can, use some, and month later open again to find it has slight skin on top; I will scoop out the entire skin and toss it in trash. Then use what I need of clear liquid, while disposing of the rest not used in the next week or two; as it’s not going to last much longer. But if I open a can that looks cloudy or thick/sludgy, it’s toast.

Based on reading of mfg literature: Unopened new cans are usually good for 2-3 years, sometimes longer if kept in cool place with reasonably consistent temperature and low humidity.
Most mfg suggest a 1 year shelf life for partially used cans properly sealed.
Preventing oxygen and moisture exposure by purging excess air (IE stop loss bags), or replacing with dry inert gas (bloxoygen/nitrogen/argon) will extend opened can shelf life to same 2-3 years of unopened can.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

10 year old poly? Trash it.

IMHO – It s just not worth the trouble to test fate and use old finishes on any hand built project that you care how it looks when done.

- CaptainKlutz

I think this will sum it up for most folks. Is it worth the chance you are taking, because as soon as you slop some on, you can’t un-slop it. It certainly is a, “better test this on some scrap” before trying to ruin my newly made, and SANDED project. I often get more time in the final prep, as the entire project.

-- Think safe, be safe

If the finish is oil based and unopened, it’s almost certainly still good. If it’s water borne, I wouldn’t chance it. Jewitt wrote an article a few years back and opined that solvent based finishes will keep indefinitely if not opened. His view on water borne finishes was that life was close to 2-3 years whether opened or not. IME, that’s pretty much the way things work. My varnish stash has several cans of unopened oil based varnish at least that old and I’m still using them…no problems whatsoever. I would guess the sludge (if this is a reduced sheen can, like semi gloss) is simply the flatteners separated out. On the other hand, I can understand the “why take a chance” aspect so tossing it isn’t that big a deal.

-- Our village hasn't lost it's idiot, he was elected to congress.

i agree with all why chance it buy some fresh stuff,not worth screwing up a project.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

In the trash with it or I have used old finish, not 10 years old, maybe 2 years, on a MDW work bench top. Got rid of the old stuff safely and sealed the top. Finishing is difficult enough without chancing bad results with old finish.

-- Les B, Oregon

Well, sounds like I dodged a bullet on this one. I had ran down to the local Ace hardware store and gotten a small can just for this particular project, hoping that maybe I’d get the “all clear” to use the older stuff on some other projects.

Guess I’ll pitch ‘em in the dumpster and start fresh.

Thanks everyone!

Can you pitch them in the dumpster? Or do they have to be disposed of in a different way?

In most locations you cannot, waste pickup is almost always “solid” waste. You can let it dry, or pour it on something (I use sawdust for such things) like kitty litter it that oil soaker stuff, then throw that in the trash. If it’s an oxidizing oil (like BLO) you would want to let it harden on the absorbent before sealing it up in a trash bag. There is no reason to consider varnish as an oxidizing oil.

-- Our village hasn't lost it's idiot, he was elected to congress.

For the sake of discussion, how long would it take an opened quart can of Helsman polyurethane to solidify to the point of being ‘acceptable’ for disposal?

For the sake of discussion, how long would it take an opened quart can of Helsman polyurethane to solidify to the point of being acceptable for disposal?
- Monte Milanuk

IME – a very long time. Month or more, depending on amount and temperatures.
You don’t want any liquid finish in your trash – landfill.
Once the top surface skins the rest cures much slower. You have to break the skin and stir it many times sped up process.
I’m constantly stuck with half full quart cans of Arm-R-Seal that have turned sludgy due heat in AZ desert summer.

My method of disposing of old finishes is simple:
Take some of those Amazon boxes that your wife is constantly having delivered full of stuff she doesn’t need, and paint the inside surfaces with excess finish.
Let it cure out back near the trash can.
If there is more left in can;
Leave the 50 cent disposable paint brush in can when done, and when the box is dry, break the skin on can, and pour/paint another coat in box. Can slop finish inside a box once every 24 hours for 2-3 days and kill a quart easy.
Toss the ‘finished boxes into trash, not recycle.

YMMV

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

I’d pitch it. Imagine taking your brand new project and dumping maybe-maybe finish on it. Just not worth it.

-- Most of my public projects: https://www.youtube.com/makethings