Preserving Leftover Paints and Varnishes

Posted by at 12:04PM - Comments: (13)

Bloxygen displaces air in the container with inert argon gas.

One of the counterintuitive fall rituals is to renew your varnish and finishes before putting your boat into storage. After all, who is going to admire your work while the boat is under wraps or in the boatyard? Varnish and sealers keep out moisture that can eventually damage the finish, creating more maintenance in the future. Moisture intrusion doesn't stop just because your boat isn't out sailing. 

Perhaps the best reason to touch up or add another coat of varnish in the fall is to avoid having to do it in the spring, when you are anxious to get back in the water and have so many other critical tasks to carry out. But once your varnish work is done, and you are now left with several cans of very expensive marine varnishes, and other marine coatings—some opened, some untouched—that you don’t want to go bad. What to do?

Stored in a dry place at room temperature, an unopened container of most of the varnishes and wood finishes will last anywhere from three to five years. However, some unlined metal cans will corrode surprisingly fast, so protecting the can with a corrosion preventative may help extend the product’s life. Keep in mind that even though a product appears a slightly different color after some time in the can, it may be fine once applied. It’s good to apply it to a test patch before throwing out a batch.

Once a container is opened, a multi-year shelf life is not guaranteed, but here are things to preserve the product for another season:

• Store it in a cool, dry place with the cap tightly sealed. (Some woodworkers suggest storing cans upside-down to better ensure a tight seal.)

• When using the product, avoid introducing contaminants into the can by pre-mixing and then pouring it into another pot for application.

• Meticulously clean the lid and lip before closing. The catalyst containers for some two-part finishes can cement shut.

• Reduce the amount of air left in the can. You can put the remains in a smaller can (available at most paint stores). We've also heard of people putting marbles in the can to raise the level of the varnish back to the top.

In addition to the above tips, a few readers have recommended pumping half empty cans of varnish with a product called Bloxygen. Bloxygen contains pure argon, a naturally-occurring gas used for welding and in packaging bagged foods like potato chips. The gas displaces oxygen in the container container, helping to preserve the contents.

A .40-ounce can is available at various internet retailers for about $10. When ours came in the mail, it was so light, we were certain we’d been sold an empty can of "Florida sunshine." However, according to the maker, each can is good for 75 quarts. Pumping the stuff into the coating’s can requires no fancy handwork, but make sure the can’s rim and lid are clean and still seal tightly. When you spray, avoid spraying directly into the varnish or paint because this can cause it to splash out.

Does it work? In 2008, we counted several cans of marine varnish left over from our test of wood coatings. As is our policy, we ended up donating most of those to local charity (the Sarasota Youth Sailing Program is one of our current partners), but we kept a few for follow-up testing. This year, almost four years later, I opened up a half-empty can of Epiphanes Rapid Clear that we’d sealed with Bloxygen, and I couldn’t tell the difference from the original in the way it looked, smelled, or applied.

The same, however, couldn’t be said of all the varnishes we protected. The two-parts seemed the most vulnerable, but this may have been due to some negligence on our part. Of the eight cans we sealed, five showed no sign of deterioration.

Bottom line: Based on our experience, Bloxygen is worth using for those who have multiple cans of expensive coatings to protect, but success isn’t assured with all products, particularly two-part wood finishes.



Comments (13)

I've been putting varnish in caulk tubes (you can get new ones from a number of places) and storing it for reuse with no issues. You use a caulk gun to meter out only what you need, even small amounts and the varnish seems to last with no issues for at least a few years - that's the most I've ever had to store before using it all. Full disclosure - a good friend of mine showed me this technique, I did not come up with it.

Posted by: Mindscape | December 4, 2018 10:29 AM    Report this comment

I have not had good luck with bloxygen. From the 10 or so cans (I'm rebuilding a boat) I've used, about half of them with bloxygen, it seems as though they go bad faster. I have a tig welder though so I can dump argon in there easily. I'll try that on this next can.

Posted by: Marcus Ward | December 4, 2018 9:10 AM    Report this comment

On used varnish, I use to fill the can with marbles -which worked but the cleaning up was not fun. At the 2016 Mystic wooden Boat show , Epifanes booth had "StopLoss Bag". Works great even with 2 year old varnish.- still have to filter it.

Posted by: Jim d. | November 15, 2018 6:57 PM    Report this comment

If the top cannot be well-sealed due to dried paint, aluminum duct tape (PS February 2018) makes an impermeable barrier. Solvents can go right through polymer tapes.

Computer dust-off compressed gas products generally contain petroleum-soluble gases. Although they initially displace air, they will soon dissolve in the paint, causing air to be drawn into the paint can, defeating the purpose. The does not happen with argon.

Posted by: Drew Frye | November 9, 2018 1:10 PM    Report this comment

I have found all of these to be well worth the effort. As a side note on the oil base paints I keep a small can of Japen ( Japan) dryer in my batch of paint cans so when I get ready to use the paint I put a few caps full of it in the paint i'm using. This replaces the drying agents and allows the paint to dry hard as original.
Hope this helps

Posted by: Captain Rhan | November 9, 2018 10:54 AM    Report this comment

Great tip, thanks. Could you comment on my more primitive practice, laying a sheet of plastic wrap (e.g. Saran) on the surface of the paint and pressing against the sides of the can. Seems to work OK, but I haven't done any 'trials' against the oxygen exclusion techniques.

Posted by: Martin Fraser | November 9, 2018 9:32 AM    Report this comment

I am welder also and been doing this with argon for years.
It also works great for potato, bread and other food stuffs.
I just barely crack open the regulator and let run for a minute or two with the lid or bag or whatver just open enough to get the hose into.

Posted by: Froat | November 8, 2018 12:23 PM    Report this comment

Agree with many comments above -- I have been adding enough compatible solvent (e.g., turps, mineral spirits, water) to the finishing product before sealing, just enough to cover the entire exposed surface in the can. It works very well to prevent skin formation. After it has had a while to saturate the atmosphere in the can I sometimes give the can a vigorous shaking ... and sometimes I don't. Either way, it doesn't seem to make a difference.

Posted by: hwpratt | November 8, 2018 11:27 AM    Report this comment

A trick I learned when building flyrods was: Grab a straw (a good reuse for the ubiquitous plastic ones). Take a deep breath. Place the top as if it were being closed. Lift an edge and exhale through the straw into the can. Quickly seal the top.

This replaces the air remaining in the can with the carbon dioxide one exhales. Seems to work OK for me.

Posted by: gkjtexoma | November 8, 2018 11:24 AM    Report this comment

A quick look at the periodic table shows that Argon is heavier than air and is a noble gas. It has an atomic weight of 40 whereas the atomic weights of oxygen and nitrogen are 16 and 14, respectively. When Bloxygen is sprayed into the can, the argon naturally sinks beneath the oxygen and nitrogen within the air overlying the liquid in the can. Old timers have told me to exhale in a can of varnish before sealing. Breath contains excess CO2 (relative to air) and CO2 has an atomic weight of 44, so presumably, the CO2 displaces the air in a similar way to the argon. However, the advantage of argon is that it is a noble gas and is thus chemically inert.

Posted by: Winsome | April 28, 2017 2:02 PM    Report this comment

Thank you for the review! Bloxygen has been helping the finishing community for over 20 years now. We have some great videos. Just search for "bloxygen videos" on YouTube.

If you have any questions, just drop us a line. I bought my first sailboat at age 10 and have sailed ever since.

Posted by: BloxygenBoy | April 27, 2017 11:52 AM    Report this comment

I have worked with all kinds of paints and Varnish's for many, many years, from my youth as a deckhand on the Great Lakes ore boats, a midlife stint painting houses,and for the last 26 yrs. on yachts of the Pacific NW. For Varnish and enamels ( including Brightside, etc.) any kind of mineral spirits based paint, when you are finished with a can and plan to put it on the shelve for a spell, pour a thin layer of solvent on top and then seal the can, try not to shake it up, and put it on the shelve. It will be just like new for years to come.

Posted by: BrightWork NW | April 27, 2017 11:21 AM    Report this comment

For varnish I just put a tablespoon (more or less) in the quart can before sealing it up. After sealing the can I turn it upside down for half a minute or so, to help seal the lid. After several uses I end up with varnish stalactite on the top of the can. NOTE: the varnish I use says "contains petroleum distillates" on the label.

For my bottom paint I buy some quart can and decant the paint into them. My bottom paint is water based so I follow the same procedure but with water.

Posted by: mark maugle | April 27, 2017 9:09 AM    Report this comment

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