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Spar varnish or tung oil.

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Subject: Spar varnish or tung oil.

Email question:

I have Teak wood on my boat. It gets wet from time to time and is in full sun most of the time. I am in need of refinishing it and have heard several different ways of doing it. the two most recommended are Tung oil and Marine Spar Varnish. What would you recommend?

Marc

Email reply:

Hi Marc

The best formulated and highest priced Marine Spar Varnishes are made with tung oil as one of the main ingredients.

Resins (the best use phenolic), solvents, driers and UV protection are combined with tung oil to make the spar varnish. Spar varnish was designed with a high oil content for varnishing spars, so it has good flexibility.

Spar varnishes made with linseed, soya or most other oils will deteriorate over time and may chip and flake. Spar varnishes made with tung oil will "chalk off" over a period of time, so the old finish can be prepared and a new coat applied over the old.

If you're applying just a clear coat without staining the wood first the spar varnish with UV protection would probably be the best choice for the protection of the wood under the finish.

Then there is tung oil. Tung oil itself is one of the finest finishes there is, but you need to watch closely to be sure of what you're getting when you buy tung oil. For starters, there is 100% tung oil, but be sure to read the label and ingredients, because some manufacturers believe that the tung oil they use is 100% tung oil, but they add solvents to make the tung oil more workable, so you're getting 100% tung oil with solvents.

Straight 100% tung oil is difficult to work with, because it's thick and you need to apply very thin coats to have it dry and cure properly.

The more honest manufacturers will call their product something like Tung Oil Finish, which is generally tung oil cut with solvents to make it more workable and driers to make it dry quicker. Some manufacturers will add UV protection too. It's best to stay away from any urethane ingredients.

Tung oil doesn't need any UV protection for itself and if you stain the wood with pigmented oil stain that will pretty much take care of the UV protection for the wood. Teak is pretty tough stuff and resists deterioration from the UV rays anyway. Most woods will look better if they're stained with a neutral color stain anyway to even out the color.

Then there is polymerized tung oil. You may see different tung oil finishes with different amounts of gloss. Generally to get the different gloss levels different amounts of polymerized tung oil are used compared to the solvents. Polymerized tung oil should have some UV protection for itself as it isn't as hardy as 100% tung oil, even cut with solvents, but the UV protection isn't a must, it just means that you may have to apply a new coat of tung oil a little bit sooner than you would with the UV protection. Non-polymerized tung oil has more of a sheen than a shine.

Polymerization is a natural process, but polymerized tung oil is 100% tung oil given a little help by heating to get part of the polymerizing done quickly, so the end product will dry quicker and will have a higher shine, but will usually have to be cut more with solvents, because the straight polymerized tung oil is kind of gooey and almost impossible to work with.

The smart people who know such things say that polymerization is the combination of monomers to make a polymer and a monomer is a molecule that can combine with others to make a polymer.

The teak oil molecules are very small, so they can get into the wood easily and the natural polymerization means that each successive coat of tung oil will bind itself to the previous one to make a thicker protective coat.

Tung oil will generally take 24 to 36 hours to dry, but a little japan drier can be added to speed up the drying process, but too much will cause the tung oil to be less durable.

If you clean the tung oil finished wood every few months and apply another thin coat of tung oil it should last indefinitely and always look new.

In a nutshell, I would recommend either one or the other, but I hope the information will help you to make your decision.

There is a good product called Chinawood Deck Oil that's designed for use on decks, but is good on anything. It's 33% tung oil with solvents. You can see a little more about it in a PDF file at Chinawood oil