In the February, 2015 issue of Popular Woodworking Magazine I wrote an article on teak oil. If you’re interested in a more extensive explanation than here, I encourage you to go back to that issue and read the article.
I titled the article “Teak Oil: The Oil That Doesn’t Exist,” because there’s no such thing as teak oil. I had suspected this from as far back as the early 1990s – that teak oil was snake oil, that it had nothing to do with teakwood, and that it had no special qualities that made it a better finish for teak. But I was basing that on just a few brands. I had never collected, analyzed and tested a large number of brands.
In the last decade both my sons moved to cities on the West Coast with seaports and marinas, so I decided this presented a good opportunity to collect lots of brands, maybe all of them, actually.
Over several years I brought them home and began figuring out what they were and how they performed when exposed to sun and rain, primarily the sun. We know what happens when water gets through or under any coating. It peels.
The issue I wanted to test for was UV resistance. There are two conditions that have to exist for a coating to provide UV resistance. First, it has to contain either pigment or UV absorbers (or both). Pigment absorbs UV light, the reason paint works so well. UV absorbers are chemicals that break down UV light before it gets to the wood. Second, it has to dry hard so it can be built up to a thickness on the wood. Sunlight slowly breaks down pigment and UV absorbers, so if there’s no thickness, the coating loses it’s resistance quickly.
The thicker the film the longer it takes for the UV light to break down all the pigment and/or UV absorbers, so the longer it takes for the UV light to reach the wood. When it does reach the wood, it breaks down the lignin, and the surface cellulose fibers lose their bond to the wood. We see this as the wood turning gray when the wood is uncoated. The result is that finish or paint peels away.
Wooden boat owners typically deal with this by extending the life of the film to put off the day when they have to strip everything and start over. They begin by applying as many as eight or more coats of a UV-resistant varnish. Then they sand off several layers of the film and add several fresh layers every six-months-to-two-years depending on how far south or north they live and the amount of exterior exposure the boat receives.
The thirteen products I tested were labeled “teak oil,” didn’t contain pigment and in some way claimed UV resistance. With one exception, none of them were capable of building a film because they didn’t dry hard. The exception was Briwax Teak Oil, which is wiping varnish, so it can be slowly built up. But it showed no UV resistance in my tests, and the instructions didn’t say to build a film, so I really doubt it contains UV absorbers.
I also tested several other products sold in marinas for teak but were not labeled teak oil. They also weren’t capable of building a film, and they broke down quickly in sunlight.
So what did I determine the products labeled teak oil actually were? Simple mineral oil, linseed oil, tung oil or oil/varnish blend. One was a mixture of wax and turpentine. Then, of course, there was the one wiping varnish.
All snake oil when it comes to providing UV resistance (or moisture resistance for that matter).