Treated fence posts are any variety of post used in the construction of a fence that is treated with a protective chemical or material to make it more resistant to rusting, rotting, fading, or otherwise degrading. Wood is especially susceptible to rot and decay, so treated fence posts made of wood are a much better option than less expensive, untreated wood. Steel posts are also treated; the process is called galvanization, and the steel is coated in a chemical or material more resistant to rust than steel. Zinc and aluminum are common materials used in the galvanization process.
Wooden treated fence posts are often sprayed or otherwise coated with a protective chemical that will keep insects from damaging the wood, rainwater from seeping into the wood's pores, and mold and mildew from growing on the posts. Chemicals such as micro copper azole or alkaline copper quaternary are common choices for treating wooden posts. Such chemicals often turn the wood a greenish color, though paint can be applied over the coating to enhance the look of the post. When cutting treated fence posts, it is important to wear a protective mask, as the chemicals in the sawdust can be harmful to humans. Treated posts should not be burned in a fire if the fence is ever deconstructed.
Metal posts are also treated. Galvanization is the process of adding a material to the outside of a steel post, since steel does not naturally resist corrosion. Galvanized treated fence posts are most often used in chain link fence structures, and the chain links themselves are also galvanized. Zinc is commonly used as the coating material during galvanization, and if the fence is cut or damaged at any point, the zinc can actually coat the broken part, preventing rusting in that area. Aluminum can also be used in the galvanization process, though it is less common and it will not protect parts of the fence that are damaged.
It is important to remember that regardless of the treatment given to the fence post, if it is made from substandard materials, it will still be susceptible to rot, decay, breakage, or other types of damage. On a chain link fence, for example, treated fence posts will not do any good if the steel is too thin for the structure it is supporting. Wooden posts are even more susceptible to damage if the wood being used for the post is extremely porous, or if it is exceptionally prone to warping.