When my home was built, I wanted to make sure the slab hardened properly. I've read that concrete hardens best if wetted for several hours after it becomes firm, so I asked the builder to keep the surface wet. He said this was not necessary because special retardants are added to the concrete mix. The day of the pour, the temperature was in the 90s, the surface was not wetted, and two days later there were two quarter-inch-wide cracks. How can a builder disregard standard construction practice in this way?

Concrete cures best when it cures slowly. This is common knowledge within the building industry. On large-scale concrete projects, such as multi-level parking facilities where maximum strength is critical, workers routinely spray water on newly formed concrete. On some jobs, fresh cement is sprayed with oil to forestall evaporation and maintain the water content of the mix.