Manufacturing concrete is a relatively simple process. Portland cement is mixed with water, sand and small stones. Water is used to ensure the cement will evenly coat the sand and stones as well as fill in the empty spaces between them. The amount of water added to the mixture determines the weight of the finished product. Adding as little water as possible makes the concrete light. Light concrete is desirable when hardness and durability are the most important factors. Heavier concrete takes more water. It is used when a job requires more detail work as the concrete is easier to mold. Heavy concrete is still considered durable, and its properties make it useful in many areas.