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What material is typically used for a vapor barrier under a concrete slab?

1. 1 to 2 inch polyethylene

2. 1 to 2 inch PVC

3. 10 to 15 mil PVC

4. 10 to 15 mil polyethylene

The correct answer is: 1 to 2 inch polyethylene

The correct choice identifies the material commonly utilized for a vapor barrier under a concrete slab as 10 to 15 mil polyethylene. This thickness provides a substantial barrier against moisture migration from the soil beneath the slab to the concrete. Polyethylene is favored because of its durability, moisture resistance, and cost-effectiveness, making it a reliable choice for preventing moisture-related issues, such as efflorescence and mold growth, in finished spaces above the slab. While options like PVC also offer moisture barriers, they are not as frequently used for this particular application. Polyethylene's flexibility and resistance to puncturing during the installation process further solidify its widespread adoption in construction practices involving concrete slabs. Thicker polyethylene sheeting (in the 10 to 15 mil range) is particularly effective, as it significantly improves the barrier's capability to resist puncture and tear compared to thinner materials.