What is a common practice to follow when constructing a concrete slab?

Using a vapor barrier for moisture control is an essential practice when constructing a concrete slab. A vapor barrier serves to prevent moisture from the ground from infiltrating the concrete slab. This is particularly important because excessive moisture can lead to a number of problems, including cracking, mold growth, and issues with the curing process of the concrete.

By placing a vapor barrier under the concrete, you create a barrier that traps moisture under the slab while also inhibiting moisture from rising up from the ground, allowing the concrete to cure properly and maintain its structural integrity. This step is crucial in ensuring the longevity and durability of the slab, especially in climates or soils prone to high moisture levels.

The other options propose practices that may not yield desirable outcomes when it comes to constructing a concrete slab. For instance, pouring concrete directly onto dry soil can lead to poor bonding and increased cracking, while allowing the concrete to be exposed to direct sunlight can result in uneven curing and surface defects. Mixing aggregate with concrete in equal parts could compromise the concrete mix quality, as proper ratios must be maintained for optimal strength and durability.