Problem with Polyurethane

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Forum topic by Jon Anderson posted 03-11-2017 10:55 PM 1172 views 0 times favorited 18 replies Add to Favorites Watch
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Jon Anderson

31 posts in 2780 days

03-11-2017 10:55 PM

Topic tags/keywords: question

I buy small cans of Poly, my projects are rarely very large but even these jell quite quickly , usually with a thick crust at the top of the poly level. . Is it just the fact that the seal on the can gets bad and lets air in. If so how do you deal with that. Maybe put into another screw container that will seal better. Also as it jells can you add paint thinner to thin it out.

-- jbander

18 replies so far

View JCamp's profile


996 posts in 998 days

#1 posted 03-11-2017 11:14 PM

I don’t know how to make it stop but I’ve tried to put it in old jelly jars and such and it don’t seems to help. I’m gonna follow this post in the hopes that someone here has an answer

-- Whatsoever thy hand findeth to do, do it with all thy might

View Loren's profile


10477 posts in 4095 days

#2 posted 03-11-2017 11:57 PM

It’s oxygen. You can buy a product called
“bloxygen”... co2 I think, in a spray bottle
with a tube.

View bondogaposis's profile


5487 posts in 2799 days

#3 posted 03-12-2017 12:28 AM

Just the nature of it. Make more projects and use it up faster.

-- Bondo Gaposis

View MrUnix's profile


7435 posts in 2646 days

#4 posted 03-12-2017 12:30 AM

I pour what I need into a mason jar, then fill the can up with propane before putting the top back on. I have also on occasion cut a small circle out of a grocery store bag (HDPE) and placed it on the surface of the poly before doing the propane thing. I also fill the mason jar with propane between uses. I have a jar right now that is about 1/3 full of poly that has been sitting on the shelf for almost a year – no sign of gelling and still exactly as it was just after pouring out of the can.

The key is to open the container up as little as possible to minimize exposure, and the propane displaces the oxygen in between. Not perfect, but it does help prolong the shelf life. I’ve heard of lots of other methods as well, but the rational is the same – minimize exposure and displace the oxygen to slow/stop the poly from kicking off. Once it does, there is nothing you can do to stop it.


-- Brad in FL - In Dog I trust... everything else is questionable

View OSU55's profile


2380 posts in 2437 days

#5 posted 03-12-2017 12:33 AM

Yep, gotta displace the oxygen in the container. I use propane from my little propane torch. Just don’t pull the trigger too far…...........

View David 's profile


13 posts in 892 days

#6 posted 03-12-2017 01:14 AM

It is what Loren said. No matter how tight you put the lid back on… the air in whatever volume of space left inside will react with the product…creating the skim. As he said… there are some sprays that supposedly reduce the problem. I’ve never tried it. Another product you may like is General Finishes (satin and/or gloss) Oil & Urethane. Much better than the old polyurethane mix. The oil and urethane go on thinner…and it takes a few more coats to get the millage you want…but I’ve noticed it just doesn’t do that “skim” either.

View pontic's profile


697 posts in 1056 days

#7 posted 03-12-2017 02:14 AM

Not much else to say. Just that I punch holes in the bottom of the seal ring so the poly doesn’t splash out on me any more. If there were a syringe type container that could not let air in in the first place.

-- Illigitimii non carburundum sum

View cherk3's profile


14 posts in 889 days

#8 posted 03-12-2017 02:21 AM

I find that if I flip my containers over and place it on the lid upside down, it usually helps.

View Carloz's profile


1147 posts in 1039 days

#9 posted 03-12-2017 03:09 AM

Easy peazy.
After you done using it close the lid and turn it upside down for a second. The liquid will go in all crevices and when it dries it will be hermetically sealed. Works well with paints, lacquers, preserves, honey and all king of stuff in a jar.

View Jon Anderson's profile

Jon Anderson

31 posts in 2780 days

#10 posted 03-12-2017 03:31 AM

Great responses, great support it gives me some things to try and I like that. I appreciated it , if you got anything else let me know. Thanks!!

-- jbander

View jacww's profile


38 posts in 1455 days

#11 posted 03-12-2017 11:50 AM

I agree with storing the can upside down.

Just be sure the lid is really on securely. If the lid come off of a gallon container of paint or finish as it is flipped upside down…. well you get the picture.

Don’t ask me how I know.

I used a gallon of oil based paint for years storing it this way after each use. The paint never developed a skin. And I was anal about checking the security of the lid. (It only takes one time)


View Fred Hargis's profile

Fred Hargis

5635 posts in 2941 days

#12 posted 03-12-2017 01:59 PM

I’ve tried all sorts of O2 blockers and other tricks, I haven’t found any that are 100%. That includes Bloxygen, home made CO2, propane, and vacuum sealing. The home made CO2 is done by putting baking soda in a large pitcher, and then pouring vinegar into it. That gives off CO2, and since it’s heavier than air, it just displaces the air in the pitcher. You can then “pour” it into your finish can. (If you try this, you can prove it by lighting a match and sticking it in the pitcher; it goes out when you get to the CO2. Anyway, I also tried vacuum sealing with those Ziplock vacuum food storage bags (now discontinued). I cut the port off one and put it on the container lid, sucked so much air out the can started to deform…that didn’t work all that well, BTW. I think maybe putting marbles (or small clean rocks) in the can to get the level to the top works the best of the home made attempts I’ve tried, but it’s also the biggest mess. Now I’ve bought some of these, which is more or less the same idea: no air in the container….so far I haven’t had a chance to try them but I have high expectations. One tip though: the curing is a chemical process that starts when the finish is exposed to O2. Lower temps generally slow chemical reactions, so putting it in a fridge (I always do that) for storage really does slow it down.

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

View Bill White's profile

Bill White

5215 posts in 4408 days

#13 posted 03-12-2017 02:19 PM

Open the top a bit and exhale (after a good, strong inhale).
Works for me, and I despise poly.

-- [email protected]

View splintergroup's profile


2763 posts in 1670 days

#14 posted 03-12-2017 02:53 PM

I use a squirt of CO2 from my mig welder, but Argon would be better.

Non-gas methods that have worked for me (with gallons of latex) is to place a piece of saran wrap down over the surface.

Box-o-wine bags work great, you can squeeze out the air and then have a handy push button dispenser (I think Lee Valley sells the same thing).

View Kazooman's profile


1333 posts in 2400 days

#15 posted 03-12-2017 03:05 PM

Go easy on the stirring so you don’t whip a lot of air into the poly. Filling the head space with an inert gas won’t help if you have beaten a lot of air into the liquid. Pour out what you think you will need into another container to work from and close the bulk can. Don’t return any leftover to the original can.

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