Wood is made mostly of cellulose and lignin. Cellulose is fibrous and gives wood its strength. Lignin is a kind of natural glue that holds the fibrous stuff together. Wood has enemies, mainly bugs, water and sunlight. Bugs eat wood. Ultraviolet (UV) light changes the lignin molecule in wood so that it loses its adhesive properties. The lignin leeches out of the wood, leaving a rough, fibrous gray surface. If you apply a finish to the wood–a stain or sealer or paint–you can slow the process down and help your furniture last longer.Of any exterior finish, paint offers the best form of protection, but it’s the most difficult to maintain. Paint will eventually peel and will be more unsightly over time than a wipe-on finish like a sealer or a colored stain. In fact, most outdoor finishes will only last 1-3 years before they need to be renewed. That takes a commitment on your part to periodically protect your furniture.Regardless of the finish you choose, you should wipe off dirt or grass clippings and wash your furniture periodically with mild soap and water. Application of a sealer or stain every few years will continue to protect the wood.Important: Do not leave chair or table legs in contact with the ground for extended periods of time. This is a prescription for rot. Your furniture will last much longer if it rests on bricks or concrete or flagstone–any kind of hard surface that doesn’t retain moisture and harbor insects.If you don’t intend to renew the finish on your outdoor furniture, the wood will turn a silvery gray color and last for many years with periodic cleaning and by keeping it off bare ground.