Beyond the Build

Tips from the Field

Eliminating Moisture: Flooring’s Arch Rival

In the final stages of a recent project, we discovered that our concrete slabs had elevated moisture content as compared to the specifications required by the desired floor coverings. This persisted in spite of running the HVAC system for 30 days, our standard operating procedure.

Was their storm water matriculating through sub grade? Was there a leak? Did our vapor barrier have a breach? While I had asked the question about openings, the reality was that we were not managing egress and ingress enough. In the process, we were trying to dehumidify the universe. Sometimes, we all overlook the simple. In this case, the solution was to keep the doors closed.

Floor coverings are affected to one degree or another by PH issues and excess water vapor emissions through a concrete slab. Moisture can cause failures across the board if not managed. In the case of LVT, it can cause gaps in the joints, adhesive release or with carpet delamination. Left uncorrected, these problems can evolve into health and safety issues caused by mold, mildew and floors lifting.

A few things we’ve learned (sometimes the hard way)

  • Ready-mix concrete. Adding water to concrete onsite increases workability, but it also can increases moisture in a slab.
  • Minimize below slab moisture transmission by the using an intact vapor barrier.
  • Consider the size of granular fill. Granular fill is intended to have large enough voids to prevent moisture wick.
  • Surface cracks should be filled to deter moisture transmission. However, expansion joints should not be filled.

Most importantly, if the substrate is not right, the floor will not be long term.

Merrill Stewart Jr.

Merrill Stewart is Founder and CEO of The Stewart/Perry Company, a commercial building contractor based in Birmingham.