Thinning General Arm-R-Seal urethane topcoat that might have dried out a bit?

[John W Henderson]

I'm an extreme novice when it comes to finishing. I went with General Arm-R-Seal oil & urethane topcoat (semi-gloss) as shown HERE since it was an easy to use wiping finish. After using it for several small projects, subsequent layers must have accumulated in the trough such that the lid didn't seal anymore (but I didn't know this). I used it in March on a project and then didn't need it until recently in perhaps July/Aug. When I went to open it, it opened extremely easily and I realized the issue with the seal.

I tried it on a piece of wood and it seemed a bit thicker. Not unusable, but it seemed "gelled" up right away vs. my remembering having a couple minutes of open time before it started to thicken just a bit. The can says not to thin it, and I'm inquiring about why this is and if it's possible that I could add something to it to be able to use it.

Again, it's not horridly ruined, and I have quite a bit of the can left and would love if it was just a tad more thin. It wants to streak as if it's just a tad too thick to really wet out the surface smoothly before drying (thus, when dry it shows the applicator lines here and there).

Any suggestions?

I guess I could just try some in a small container, but thought others might know why the can advises against thinning.

[Harvey Pascoe]

If it has not GELLED, then you can thin it no problem, otherwise toss it.

[Howard Acheson]

Being frugal and using possibly damaged finish is not a good idea. If it has been improperly covered for the period of time you say, it will have begun to oxidize from its long term exposure to oxygen.

After all the time and money you have invested in a project, buy new product to ensure that it gets finish properly. After all, it's the finish that earns the "oohs and ahs", hot the joinery.

In the future, pour out what you need into a separate container or pan. Then immediately wipe out the seal and securely cover the can. Never work from the original can. Never pour unused decanted finish back into the original can. Every time the can is opened it is exposed to oxygen. Oxygen is what causes oil based finishes to dry and cure.

[John W Henderson]

@Harvey: How do I tell if it's gelled and not just thickened up a bit? It's pretty darn thin, just not quite enough, it seems.

@Howard: Yeah... you make some excellent points. I'm being pretty stingy considering I think it's only like $13 for a pint or whatever size the little thing is. I was just bummed I had so much of the can left and had this happen. Thanks for the tips about working out of a separate container and wiping things down. I dumped it all into a cleaned out salsa jar that's easier to keep clean and seal for the time being.

[Scott Holmes]

Howie didn't mention it but displacing the air in the can really goes a long way to eliminating the oxygen curing the varnish while the can is sealed. Use CO2, or Argon, Propane (no smoking if you use this), or a product called Bloxygen all these will displaces the oxygen in the can with a mixture of inert gases and no skinning over will occure.

[Jon Hayman]

The Arm-R-Seal Gloss is the best oil-based finish I've ever used to both bring out the grain of the wood and leave the wood color looking natural. It doesn't yellow like polyurethane or varnish-type wipe-on finishes.

I've had the same problem with the finish thickening in the can. The finish left in the original can has a short shelf-life {a couple of months}. It will eventually turn into a jelly-like mass, and with my experience with it the last couple of years, I've found that it can't be restored with regular paint thinner to its original thin consistency. I can get a little less thick jelly mass if using quite a bit of thinner, but nothing more. Maybe there's a specific type of thinner that can be used, but when I emailed the company, they thought any thinner should work. You can still use it in a thickened state as a wipe on/off finish, although it will be more time-consuming to work with. Bloxygen will slow down the gelling process, but won't stop it. Only buy it in small cans or as much as you think you will use in a couple of months. I haven't tried switching the left over finish to smaller cans as it's used up, so that will be my next experiment.

Also, if you are using the wipe on/off method, wipe it off fast. It dries very quickly compared with other polyurethane and varnish finishes, and will start to "grab" at your wiping cloth if you don't get it off fast enough.

Even given the above issues, I still buy it because it's the only finish that gives the look I want.

[Chris Fournier]

Not worth the potential disaster. You are not effectively thinning a useful finish, you are thinning a spent finish that will mess up your project like you never imagined. "False economy" is a phrase you will understand very quickly!

[Sam Stephens]

my understanding of the "do not thin" regards vocs (volatile organic compounds). If you thin it such as w/ mineral spirits or paint thinner, the vocs would be above the critical value allowed as determined by some agency. So yes, you can thin it. Just make sure you stir it well, particularly the semi-gloss and satins which contain flatteners. Those agents need to evenly mixed/distributed rather than settling and accumulating at the bottom of the can. As for using a questionable finish, not worth the risk imo

[Howard Acheson]

>>>> It doesn't yellow like polyurethane or varnish-type wipe-on finishes

Arm R Seal is a polyurethane. It's been highly thinned to allow it to be wiped on. It will yellow over time just like any other oil based finish. Adding a thinner to a gelled residue will not produce a properly behaved finish. By gelling, the finish has started to combine with oxygen and begun to oxidize. While it may seem to dry, it will not fully cure and become a hard, protective finish.

It's not worth possibly compromising the project by trying to save money resurrecting a gelled finish.

[Adolph Hofmann]

I asked General Finishes about Arm-R-Seal that had gelled, and here is what they said: "You can add mineral spirits to a point. If it is newer material within 1 year of manufacture date which should be on the bottom of the can, then I would say go ahead and do it. If it has been sitting for 3+years then it is time to just get rid of it as a lot of the driers go out of products after that long, and you don’t really want to start a new project with bad product that does not want to dry. You and always test it by applying some on a test piece and let dry overnight… if it is dry then you can use it if it is still tacky after two days I would not use it, at this time of year [late September] 1-2 days for dry time is pretty standard."

Art Hofmann
Santa Rosa, CA

[Howard Acheson]

>>>> 've had the same problem with the finish thickening in the can

Arm R Seal is a thinned poly varnish. When a varnish has had lots of thinner added to it, it will significantly reduce the shelf life.