What are the common reasons for an unfinished exterior door and how can it be properly treated or finished to ensure durability and longevity?

Common reasons for an unfinished exterior door include improper sealing, exposure to harsh weather conditions, and lack of maintenance. To properly treat and finish an unfinished exterior door for durability and longevity, it is important to first sand the surface, apply a primer, and then finish with a weather-resistant sealant or paint. Regular maintenance, such as reapplying sealant or paint as needed, can also help protect the door from the elements and extend its lifespan.