Chimneys and stacks appear to be strong and indestructible, but chimneys begin to deteriorate from the moment they are built. Early on, no signs are apparent; but deterioration accelerates in subsequent years, and major repairs are soon needed instead of minor maintenance. With proper attention, most structures can be repaired and continue to serve for years. Many factors contribute to deterioration. A chimney's height, slender form, and unique function create an environment different from that of other structures. Degradation is accelerated, and risks are magnified. Reinforced-concrete chimneys have three major causes of deterioration: (1) flue gas itself; (2) when the liner itself begins to deteriorate and the chimney is exposed to hot gases; and (3) carbonation. Wind, rain and fluctuating ambient temperatures can also effect chimneys and stacks. Chimney repair professionals have many coating options available to protect chimneys. These include specialized coatings that can withstand a range of chemical and thermal conditions. Concrete chimneys are coated for three reasons: (1) protection against environmental elements; (2) protection against process gases; and (3) compliance with Federal Aviation Administration (FAA) requirements (flashing lights for nighttime and warning paint for daytime). The best approach to minimize the risk of a costly repair or rebuild is to start by shifting the focus from short-term maintenance to life-cycle costs. Examine the original chimney design and learn what types of stacks, liners, and coatings were used. Maintenance cannot be avoided, nor should it be, but a comprehensive preventive-maintenance program is likely to decrease overall repairs.