Red Seal Concrete Finisher Practice Exam

What is the purpose of installing a vapor barrier under concrete slabs?

1. To improve the curing process

2. To increase structural support

3. To prevent moisture intrusion

4. To enhance insulation

The correct answer is: To prevent moisture intrusion

The purpose of installing a vapor barrier under concrete slabs is to prevent moisture intrusion. Moisture in the ground can rise and migrate through the concrete, leading to issues such as mold growth, concrete deterioration, and damage to flooring systems placed on top. A vapor barrier effectively blocks this moisture from seeping through, thereby protecting the integrity of the concrete slab and the materials above it. By preventing moisture from entering the concrete slab, not only is the concrete itself preserved, but also the quality of any flooring systems, finishes, or furnishings placed on top is maintained. This is particularly important in areas with high groundwater or where the concrete slab is situated directly on soil or vapor-retaining materials. The other choices relate to aspects of concrete construction but do not accurately reflect the specific role of a vapor barrier. For instance, while curing is important for the strength and durability of concrete, it is more closely associated with moisture retention in the concrete itself rather than preventing moisture from below. Structural support is typically provided by the concrete mix and reinforcement rather than a vapor barrier. Insulation can be enhanced through other materials specifically designed for thermal performance, but this is also not the function of a vapor barrier.