Redwood is naturally gifted with a compound called Tannic Acid. Tannic acid is the natural chemical which gives Redwood Insect resistance as well as rot resistance. This will allow you to enjoy a Redwood deck for many years to come. Tannic acid will produce tannins which will bleed a dark color. This will NOT harm the wood. However, the appearance will be compromised a bit by the tannins. There are several products on the market that will last two years and sometimes three years without refinishing the deck. The wetter the climate the more often the deck will need to be refinished. This is true with all good lumber decks. However, the natural elegance of a Redwood deck is more than worth the occasional power washing and reapplication of a good sealer! With care, a good Redwood deck can give 30-40 years of outdoor enjoyment!