What is one reason concrete may be coated?

Coating concrete for waterproofing purposes is a common practice in construction and maintenance. Concrete is naturally porous, which means it can absorb water and other liquids, potentially leading to damage such as cracking, spalling, or corrosion of reinforcing steel over time. By applying a waterproof coating, the surface is sealed, preventing water infiltration and extending the lifespan of the concrete structure. This is particularly important in areas exposed to moisture, such as basements, foundations, and outdoor structures, where prolonged water exposure can cause significant deterioration.

Other options, while related to various properties of materials, do not align with the primary reasons for coating concrete. For example, increasing weight or changing density would not typically be desired outcomes in concrete applications, as they could lead to structural challenges. Enhancing flexibility is also not a common reason for coating concrete, as concrete is a rigid material, and coatings are typically employed to improve durability or performance rather than flexibility.