Here’s the truth most people don’t realize about vinyl flooring over concrete slabs: Concrete naturally holds moisture. Even when it feels “dry,” vapor is constantly moving up through it. When you cover that slab with a tight, waterproof material like vinyl, the moisture has nowhere to go — it gets trapped underneath. Over time, that trapped moisture can lead to mold growth on the underside of the vinyl or on the slab itself, especially in basements or lower levels with limited airflow. The floo