All concrete floor slabs contain moisture. Consider this true even if the slab was poured many years earlier. It’s just the nature of concrete. Concrete’s three main ingredients (water, cement, and aggregate) function together to give concrete its characteristic hardness, strength, and durability. Without water, concrete would simply not be concrete at all.
When preparing to install a finished floor product over a concrete slab, you want to be sure that you won’t run into problems stemming from the concrete’s moisture condition. But it’s not a question of whether the concrete is dry or wet. No matter how dry the slab may look at the surface, rest assured, it’s not completely dry. Again—by design—all slabs contain water.