Preserving oil base finishes

[julian abram]

It always frustrates me open a can of used oil-based finish a month later to find it separated and filmed over. Any tips or suggestions for removing air from cans or additives that will prevent this for a reasonable time frame? I read somewhere a fellow stored his oil based finishes in wine bottles and used a special cork to evacuate the air.

[John TenEyck]

The two easiest ways of dealing with that problem is to use a product called Bloxygen to displace the air, or add clean marbles or pebbles to the can until the liquid reaches the top.

John

[Jamie Buxton]

The secret to preserving half-full cans of finish is to close the can. Think about it -- a can may sit on a store shelf for months or even years, and the finish remains viable. Look at the lid and the top of the can. The lid fits into a channel around the top of the can. There's actually two metal-to-metal seals. One is on the outside edge of the channel, and the other is on the inside edge of the channel. Solvents escaping, or outside atmosphere getting in, have to pass through those two seals. If the seals fit tightly, the finish stays okay. Usually, the seals are not sealed because there's finish in the channel. The finish prevents you from getting the lid all the way tightly down on the can. The fix is to clean out the channel before you close the lid. If you do it right, the lid will close flush with the top of the can, just like it is when you buy it. If the lid is not down flush, the seals are not sealing, and the finish in the can will go bad.

I've had properly-sealed half-filled cans of finish survive for years.

[Scott Holmes]

Jamie, A full can has little to no air tapped inside the can. Manufacturers may even add an inert gas when they package it. A half empty can has a lot of air trapped inside; the oxygen in the air reacts with the finish. Hence the crusty top. Bloxygen or any other inert gas will displace the air and preserve the finish. I use argon gas from my MIG welder or Bloxygen. On occasion for short periods of time I have even held my breathe as long as I could then gently exhaled the mostly CO2 into the can. A tight seal is good but can't stop the oxygen IN the can from reacting with the finish.

[Jamie Buxton]

Jamie, A full can has little to no air tapped inside the can. Manufacturers may even add an inert gas when they package it. A half empty can has a lot of air trapped inside; the oxygen in the air reacts with the finish. Hence the crusty top. Bloxygen or any other inert gas will displace the air and preserve the finish. I use argon gas from my MIG welder or Bloxygen. On occasion for short periods of time I have even held my breathe as long as I could then gently exhaled the mostly CO2 into the can. A tight seal is good but can't stop the oxygen IN the can from reacting with the finish.

You're correct that the finish in a half-empty can of varnish will react with the air in the can. However, that just isn't very much air. Like I said, I've had properly-closed half-empty cans of varnish that remained viable for years.

[Rich Engelhardt]

Like I said, I've had properly-closed half-empty cans of varnish that remained viable for years.
As have I - - but - - Scott is 100% correct.
Once opened, air will get into the can.

Solvents from the material can evaporate into the trapped air just enough to prevent the material from skinning over, but, you can't always count on that to happen.

[julian abram]

Fellows thanks for the good input, sounds like the main factor is removing and sealing out the O2 by what ever means possible. I'll give the bloxygen a try and make sure cans are well sealed. Again thanks!

[Prashun Patel]

Some oil based finishes may survive an opened can, but if you are working with a phenolic varnish like Waterlox or Cabot's spar, for my money I wouldn't chance it. These varnishes seem to gel up if you look at them the wrong way. I tend to decant my varnish into 4oz glass bottles. The full glass bottles last a long time. But during a project, a bottle seems to be fine until it reaches the magic 50% mark. At that point, it gels up within a day.

I have to say, despite it's perceived shortcomings, this is one of the things I like about polyurethane. It seems to last a long time in an opened can.

[Jason Roehl]

Add a splash of whatever the primary solvent in the finish is to the top of the finish (don't stir it in, and use enough to totally cover the surface of the finish). This will then be a layer that mostly keeps the oxygen from the finish, plus it puts enough extra solvent into the air gap that none evaporates from the finish.

[Mark W Pugh]

I read somewhere a fellow stored his oil based finishes in wine bottles and used a special cork to evacuate the air.

Actually, this is a great idea. Just go to a local winery/wine making supplies store/Kohl's/wherever. They sell devices that you put a rubber stopper in your bottle, then use a pump to evacuate the air. I use these all the time on my wine bottles.

ps The corks are nothing special. These devices have been around for a long time.

[Randy Goodhew]

J On occasion for short periods of time I have even held my breathe as long as I could then gently exhaled the mostly CO2 into the can.

Know-say versus hearsay.

This is a popular Internet Echo. The problem is that exhaled air still contains about 16% oxygen, CO2 is only about 4% and the water vapor content is 100% relative humidity.
This practice can actually make things worse.

Just because it is frequently repeated, doesn't make it true.