Moisture barrier

Concrete looks solid, but it is porous. Water vapor in the ground can move up through a slab for years. When it meets a floor covering or coating, it can push it off the surface or feed mold underneath.

A moisture barrier stops that path. It can be a sheet under the slab or a coating on top, depending on the project. Graniterock, a materials supplier, advises a low permeance vapor retarder under slabs that will carry moisture-sensitive floor coverings, adhesives and coatings.

For Missouri owners, the key is to test before you finish a floor. Slab moisture can run high even when the surface feels dry. A failed coating costs far more to fix than the test costs.

Moisture also connects to indoor air. Wet slabs can support mold growth. If you plan an epoxy floor coating, ask how the slab was tested and what barrier is in the plan.