What is concrete moisture testing?

When flooring contractors in Tampa begin a residential or commercial installation, they first need to verify that the concrete substrate is dry enough to accept new materials. Concrete moisture testing accomplishes this through two primary methods that have become industry standards.

The calcium chloride test (also called the dry calcium chloride test) involves placing a calcium chloride compound in a sealed dome on the slab surface for 24 hours. The compound absorbs moisture from the concrete, and the weight gain indicates the moisture vapor transmission rate (MVTR). This result reveals whether the slab exceeds manufacturer thresholds for moisture-sensitive products like engineered wood, vinyl, or carpet.

The relative humidity (RH) probe method uses an in-slab gauge inserted into a pre-drilled hole. It measures the humidity level inside the concrete matrix itself rather than surface vapor transmission. This test provides a more direct reading of internal moisture conditions and is increasingly specified by manufacturers across flooring categories.

Both methods are critical in Florida's humid climate, where moisture migration through concrete is particularly problematic. Without testing, flooring can cup, buckle, or fail prematurely. Contractors order these tests to document baseline conditions, protect warranty coverage, and avoid costly callbacks. Building codes and most flooring manufacturers require results before installation proceeds.