These are three chairs that we built. The two on the left are our Fanback Adirondack chair, and the one on the right is our standard Adirondack chair. The two on the left are 8 years old, the one on the right is two years old. Several years ago, I did an experiment with different finishes, to determine durability, easy of application and refinishing. We applied spar varnish to one chair, and an oil finish to the other. The third chair is two years old and had absolutely no finish applied.
It is pretty easy to see that the spar varnish has held up the best over the past eight years. The oil finish is supposed to be reapplied every couple of years, but I have intentionally not done so just to see how long it would ultimately last. Clearly, you can see that the finish has worn completely through in many areas. The unfinished chair is only two years old, and has faded to a silver-gray patina. Many people like this look, because it looks weathered and reminds them of drift wood or barn wood.
When we ship your furniture out, it has been finish sanded, and is ready for the application of paint, stain, or the clear finish of your choice. Left unfinished, the grain of the wood will become raised from exposure to rain (the wood will absorb some of the moisture, and will swell at the growth rings, causing the surface of the wood to become textured. Another concern is that the wood will absorb oil from people’s hands, causing the wood to become discolored. You can see both of these conditions in the close-up of the arm rest of the unfinished chair, below.
The two chairs in our finish experiment are heavily used and abused by our 5 kids, which was part of the experiment as well. These chairs have been jumped in, stood on, drug around, hauled in the back of the truck, dropped, kicked, and generally used and abused, and have held up very well.
The area that wears the most is the seat of the chair. You can see in the photos of the seats, below, where the varnish has been chipped and scraped, and where the oil has worn completely off.
In order to renew the varnish, the existing finish should be sanded off, and two new coats applied. If you were to simply apply more varnish, the dirt and oils on the existing coat would not allow the new coats to properly bond, and they would eventually peel off. You could minimize this by washing the surface with solvent, such as lacquer thinner, but this would not guarantee anything.
The oil finish can be renewed by simply wiping on another coat. The main disadvantage is that this ideally should be done every two years, where the varnish will easily hold up much longer before needing sanded and refinished.
To ensure the longest lifespan for your furniture, a weather resistant finish should be applied. Cedar is a weather resistant wood, and will still last several years without any finish, but any wood, even teak, will eventually break down without protection.
The end result of my experiment is that I recommend finishes such as spar varnish or Thompson’s Water Seal over finishes like linseed oil or teak oil. Paints will provide similar performance to the spar varnish, when applied with a good quality primer, as will solid color deck stains.