Why do we have problems with
Concrete Moisture
What do we do?

The Dehumidification & Drying Defense Against Slab Moisture

In a “hurry-up-and-wait” construction schedule, flooring represents high stakes. Wait too long, and the project goes over-budget; install too quickly, and the floor fails. Contractors who navigate this dilemma are pushed and pulled between the needs of concrete, and the demands of employers. Both sides are likely to embrace any method of speeding up a successful floor installation.

Dehumidification is one way to encourage concrete to dry more quickly. The process reduces the dew point of the air surrounding the slab, so that moisture within the concrete can evaporate from its surface. The building industry deploys dehumidification in three ways: condensation dehumidification, heating (or drying) dehumidification, and desiccant drying.

Desiccant-based dehumidifiers draw moisture from the air by chemical attraction. Humid air is moved across a desiccant material which binds and holds the moisture. The desiccant releases the moisture and vents it away from the slab in a hot air stream. The dried desiccant absorbs more moisture, and releases it again in a continuous moisture-removal cycle. The concrete dries a little more with each cycle. Since external weather patterns do not influence this process, builders can use desiccant dehumidification all year long.

The condensation process uses cooling-based dehumidifiers to collect moisture particles. In this process, air comes in contact with a coil which lowers the air’s dew point (DP) temperature. When the resulting air cools below dew point, water vapor begins to form dew particles on the surface of the cooling coil. The remaining air is drier and is, therefore, able to absorb more moisture. Another air stream is subjected to this process and the cycle creates a drier environment for moisture evaporation.

By contrast, heat-based dehumidification raises DP temperature so the surrounding air can absorb more concrete surface moisture. The saturated air is then circulated in one of two ways. It either goes through a moisture collection system, or it releases its excess moisture outside. Either way, evaporation can more easily occur due to lowered humidity around the slab.

Due to construction constraints, most standard HVAC systems are not run for a sufficient amount of time, or at all, to aid in sufficiently drying the slab, prior to receiving a moisture sensitive flooring system. Many times this may be due to cost of running the unit, potential loss of LEED credits given for not running these units until occupancy, or extreme time constraints. Either way, the main issues are time and money. In order to have a successful installation of moisture sensitive flooring material, one or the other is going to have to be given to achieve the goal.

Successful dehumidification really requires that the concrete slab be fully enclosed so that moisture, once removed, is not re-introduced to the slab environment. Either the slab must be enclosed in service-ready indoor conditions, or a vapor barrier must be erected around it in outdoor conditions. Accurate relative humidity (RH) testing lets you accurately track moisture as it moves out of the slab. Once the desired relative humidity (RH) levels are reached, the concrete will be optimally cured to sustain a quality floor finish for years to come.

Wagner Meters can help you accurately test the RH so you can track the moisture out of the slab during the dehumidification process. Wagner offers a variety of high quality moisture meters for concrete that can verify the moisture content level.


Article by Ron Smith

Ron is a sales manager for Wagner Meters, and has over 30 years of experience in instrumentation and measurement systems in different industries. In previous positions, he has served as a regional sales manager, product and projects manager, and sales manager with manufacturers involved in measurement instrumentation.