Why is it raining inside my parking structure? Have you ever wondered why it is raining inside your parking lot? Well, it's a sign that your parking structure needs attention. Water is the number 1 cause of deterioration of the parking structure. Concrete saturated with water can freeze, expand and detach. Combined with oxygen, water can also cause corrosion of the concrete reinforcement. Exposure to thawing salts accelerates this process. As reinforcing steel expands as it is oxidized, this process also leads to concrete fragmentation. Released concrete provides less coverage or protection of the structure, which leads to further deterioration (and accelerated) if not repaired in a timely manner.