One of the most common questions I get about these fenders is "Will they rot?" I'm not sure what the right answer is, really.
"Yes.. eventually, if you don't care for them."
"They make boats out of wood, you know.."
Fast Boys are finished with a mix of Tung and Teak oil. These are what are known as penetrative finishes. That is to say they harden IN the wood (as opposed to something like Lacquer or Spar Varnish, which build and harden on the surface of the wood). This finish is surprisingly tough. It does a great job of protecting against greying and water-logging.
Some maintenance is needed, however; in the same way that you need to respray your steel frame with J.P. Weigles, and occasionally Proofide your Brooks saddle. Like most bike parts, wood fenders are a consumable.. They will eventually wear out. If you take simple steps, however, this will not happen for a very long time.
If you feel like it, wipe your fenders down with a rag when you get home after a wet commute.
Make sure your fenders are dry.
Clean them well (with a dry rag).
Buff them with steel wool.
Put on a light coat of 100% Tung oil. (follow the instructions on the tin).
Wait for them to dry.. go ride.