We frequently receive invitations to visit building locations where floor coverings have failed due to excessive moisture in the floor. Upon arrival at these sites, a significant problem becomes apparent: the buildings are built in low spots, leading to hydrostatic pressure on the slabs.

Hydrostatic pressure, combined with high alkalinity resulting from salts being pushed to the concrete slab’s surface, is a top cause of floor covering failures. When hot and cold elements combine, moisture vapour transmission and the alkalinity of the slab increase.

The dry air in air-conditioned spaces further exacerbates the issue by drawing moisture from the damp concrete, carrying salts to the surface. Consequently, the pH at the interface between the slab and floor topping becomes highly alkaline, resulting in two problems: excessive moisture and corrosive alkaline salts.


Why Concrete Slabs Get Wet

Buildings in low areas surrounded by hills on two sides often encounter issues with wet concrete. In spaces with floor coverings like offices, problems or failures will likely arise. Non-climate-controlled warehouses may experience sweating slab syndrome.

If a building is constructed on a terraced site, moisture problems are also common. Typically, these sites have elevated hills on one or two sides, causing water to flow toward a retention pond.

As a general rule, when the finished floor level is lower than the surrounding earthen grades, moisture vapour pressure increases at a rate of a half pound per foot of graded drop. For instance, a 20-foot drop would result in a 10-pound increase in moisture vapour pressure per square foot.


Installing a Moisture Barrier for Floor Coverings

Moisture vapour transmission is a widespread issue leading to floor covering failures. To address this problem, epoxy-based moisture barriers are commonly used.

Their application typically involves:

  • Steel shot blasting
  • Grinding the edges
  • Applying one or two coats of moisture-resistant epoxy coating

Each type of floor covering material has specific methods and material specifications to tackle high moisture levels. We recommend following the instructions provided by the floor covering manufacturer, and any referenced documents, during the installation process.


Flooring For High Moisture Slabs

Treating high moisture in concrete slabs has been successfully accomplished for decades. However, the recommended moisture treatment may differ for each floor finish manufacturer.

We advise using moisture mitigation test methods, surface preparation methods, and products or systems in strict accordance with the floor covering manufacturer’s recommendations. Different floor systems, such as coated floors, jute-backed carpets, rubber-backed carpets, glued carpet squares, and vinyl tiles, may require different moisture abatement treatments and moisture testing requirements.

On the other hand, a polished concrete floor will let moisture escape if it isn’t sealed. This could be a good option for your wet slab.