Ask Sail: Cetol Skin

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I used Sikkens Cetol on the bare wood on my Catalina 30, Morning Dew IV. The can was compromised over the spring, and I put the balance in a 16oz clean glass mayo jar. Last spring when I went to use it, a skin had formed over the top of the liquid, so I just cut the skin off. It is 1/8in thick. In the future, is it still OK to use? How can I store it better?

Steven Berlin, Pine Point, ME

Don Casey has written many books and articles on marine maintenance and repairs

Don Casey Replies

When any liquid coating forms a skin in the can, its chemistry is changed. This is especially a problem with Cetol, which the manufacturer cautions against thinning. Whether what you have remaining in the can is still suitable for use depends on how much of the solvent has been lost. If the finish goes on thin and smooth with your brush, it is probably fine, but if it seems thick or the brush drags, I would not run the risk. As for storing it, there is no container better than the original can, because it clearly identifies the contents and has all the instructions and warnings. But once you let air into the can, and particularly as the ratio of air to liquid increases, a skin will form. To prevent this, I use a product called Bloxygen (, an inert gas (argon) in an aerosol can with a thin feed tube. Making sure first that the rim of the can is clean, you put the lid in place with the feed tube between lid and can. A two- or three-second squirt of Bloxygen then displaces some of the air, replacing it with argon, which is heavier. Remove the tube and press or hammer the lid home. The heavy argon settles on top of the liquid in the can like a gas blanket. Because it is inert, it does not react with the liquid, so the can’s contents should enjoy the same shelf life as an unopened can. Supposedly a single can of Bloxygen can be used 75 times, but in my experience this is optimistic. Nonetheless, throwing out a single half can of Cetol (or varnish) is a $15 loss at a minimum, which makes an $11 can of Bloxygen an exceptional bargain, even if you only use it 30 times.


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