Slowly curing concrete slabs—Tips to meet construction deadlines

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Slowly curing concrete slabs—Tips to meet construction deadlines

January 16, 2018 | by Cassidy Kuchenbecker, Environmental Initiatives of North America, Inc.

Slowly curing concrete slabs—Tips to meet construction deadlines

We’ve all been there. The flooring contractor refuses to install onto the concrete until it further dries. This results in the construction schedule getting further delayed. But, for how long? Can we speed the curing and drying process?

Let’s face it. Project delays are a part of life for a project manager. By the end of the construction process, when the final finishes are being installed, the last thing the client wants to hear is that there is yet another delay. Delayed flooring installation due to moist concrete is fairly common. Worse, sometimes the flooring is laid only to have to remove the material after odors, warping or discoloration develops. Who’s going to pay for the reinstallation of the flooring and other costs associated with the delay?

Concrete moisture issues can usually be curtailed by periodic measurements of the concrete moisture during the construction process. If the moisture measurements are not lowering with sufficient speed, forced drying of the concrete can be completed. Usually this forced drying still requires at least two weeks. So, don’t think you can procrastinate and wait until the last moment to initiate the forced drying process.

Measuring concrete moisture
The most effective method to measure concrete moisture is the ASTM F2170 testing method. This method involves inserting probes into the concrete. After 24 hours, the amount of moisture can then be determined. This method requires at least three test locations for small slabs and more locations based on the total size of the slab.

Measurements are typically collected once every couple of weeks during the construction process. The measurements are charted to determine an approximate date when flooring can be installed. Often, the frequency of measurements increases closer to the expected flooring installation date to ensure the concrete is drying on schedule.

Factors that hinder drying
Concrete drying is slowed by lowered temperatures, external water on the concrete (rain and snow), elevated outdoor humidity (if the building shell is not closed) and covering the concrete with paper or other materials. If concrete drying is not proceeding as expected the shell may need to be closed and general dehumidification of the interior will likely be required.

Actively drying concrete
Actively drying concrete is not easy. Many manufacturers have offered drying systems to hasten the process; however, most of these systems are either ineffective or not more effective than traditional drying methods. In our experience, the most effective method to dry concrete is to raise the indoor temperature (which raises the concrete temperature) and to operate low-grain dehumidification units and fans. Typically, contractors will retain the services of restoration companies who have this type of equipment to respond to water releases and flooding scenarios.

Final warning
Be aware, the ASTM F2170 testing method must have the concrete at the typical service temperature in order to get accurate moisture readings. Heating or cooling the concrete slab will certainly affect the moisture measurements.

Moist concrete slabs are a bane to the construction schedule. Flooring cannot be installed if the concrete is too moist. The best way to avoid delays at the end of the construction process due to moist concrete is to actively measure moisture concentrations early in construction and intervene if necessary. Actively drying the slab typically requires several weeks, so no waiting until the last minute to determine if the concrete is dry enough for flooring installation.