Dehumidification and Drying Concrete

In flooring applications, either finished concrete or applied flooring, there is always a "hurry up and wait" element—wanting to move ahead but knowing that rushing too quickly may result in a flooring failure or problem. Meeting concrete and flooring specifications can seem like a luxury that is not always available to a contractor on a tight schedule.

 

Dehumidification is one process often used to encourage a concrete slab to dry more quickly so that it can reach the installation point. The basic concept is simple: reduce the dew point of the air surrounding the slab so that more of the latent moisture within the slab can evaporate out through the slab surface. Here's a breakdown of how dehumidification works with drying concrete effectively:

 

Why Dehumidify Concrete?

Moisture Retention: Concrete naturally retains moisture after it is poured and can take weeks to months to fully dry, depending on conditions.

Prevent Flooring Failures: Excess moisture in concrete can lead to adhesive failures, flooring buckling, or mold growth.

Speed Up Drying: Dehumidification accelerates moisture evaporation from concrete surfaces.

 

Key Factors in Concrete Drying

Moisture Content

The goal is to lower the concrete's moisture vapor emission rate (MVER) to acceptable levels, typically 3-5 lbs per 1,000 sq ft per 24 hours for most flooring systems.

Use a moisture meter to test levels before applying any finishes.

Environmental Conditions

Optimal temperature: 50°F to 85°F (10°C to 29°C).

Optimal humidity: Relative humidity (RH) in the space should be 40%-60% for drying.

Ventilation

Proper air circulation enhances drying but should not be excessive, as it may cause cracking in the surface.

 

Using Dehumidification for Drying Concrete

1. Desiccant Dehumidifiers

Effective for lower temperature environments or when high drying performance is needed.

These units use a drying agent to remove moisture from the air and work well in sealed environments.

2. Refrigerant Dehumidifiers

The construction dehumidifier is cost-effective and suitable for moderate humidity levels.

They cool air to remove moisture, then release it back into the space.

3. Combination Systems

Combine commercial air movers and dehumidifiers for faster drying.

Air movers enhance evaporation, while dehumidifiers capture excess moisture from the air.

 

Tips for Effective Concrete Drying

Test Before Starting: Use ASTM F2170 (relative humidity testing) or ASTM F1869 (calcium chloride test) to measure moisture content.

Seal the Space: Close windows and doors to prevent external humidity from entering.

Monitor Progress: Continuously check moisture levels until they meet required thresholds.

Avoid Over-Drying: Excessively low humidity can cause surface cracks or shrinkage.

 

Drying Time Expectations

General Rule: Concrete typically dries 1 inch per month, but this can vary widely based on conditions and slab thickness.

Accelerating Factors: Dehumidifiers, proper air movement, and temperature control can significantly reduce drying time.