The Wait for Concrete to Dry

Pouring Concrete Floor

A building project is typically handled in a series of stages, each of which has its own manager. The goal is always to smoothly hand off each segment of a construction project from one manager to the next without any delays. But when moisture-sensitive flooring is involved, there’s one part of a construction job that can throw a wrench in the process: The concrete slab.

What’s Required to Achieve Successful Flooring Installation?

For flooring installation to be successful:

  • The slab moisture content and pH levels need to be within optimal range;
  • The slab must be protected from external moisture;
  • Compatibility of the moisture level in the slab with both the specified floor covering and flooring adhesive needs to be attained; and
  • Moisture-emission potential must be addressed.

What are the Factors That Delay a Slab’s Drying Time?

The procedures involved with pouring and drying a concrete slab are guided by many industry standards. But the drying time for each slab is almost impossible to predict. The factors which contribute to the slab’s drying time are unique to each installation. The drying time variables include:

  • The components of the original concrete mixture
  • Ambient air humidity
  • Final service conditions
  • Surface finishes
  • Functionality of the HVAC system
  • Floating practices or rewetting

When any of the above-named factors are altered during the project, the concrete may require a longer drying time. Delays to achieving a properly dried slab can throw off entire construction schedules.

Is it Better to Wait for the Slab to Dry or Forge Ahead?

Pulling Up Damaged Floor

Lost man hours and additional costs are just two results of scheduling interruptions on a construction project. But the alternative, which is to push ahead in spite of the slab’s condition, leads to flooring failure. Ultimately, a moisture-related flooring problem is a no-win situation for everyone from the contractors and construction managers to the flooring installers, adhesive manufacturers, and facility owners. Experience has proven, that the results of forging ahead on the installation of flooring before the concrete moisture issues in the slab have been resolved, carries a much larger price tag than playing the waiting game and getting it right in the first place.

All Eyes on the Goal, Not the Clock

The ultimate goal of a construction project to end up with an installed flooring system that’s problem-free for the long term.

When the construction schedule leaves no room for moisture issues in the concrete to be properly dealt with, there’s a temptation to rush the project and invite flooring failure.

How To Know When the Slab is Ready

There are different methods which can help to speed along the drying time of the slab, such as desiccant drying and surface treatments. But how can the flooring contractor be certain that the moisture levels in the slab are compatible with the moisture-sensitive adhesive and flooring to be installed on the project?

An accurate monitoring of the relative humidity (RH) within the concrete slab is the best way to determine when the drying time has been completed.

Surface-only indicators of moisture conditions of a concrete slab, such as calcium chloride testing, aren’t reliable, in spite of the fact that such methods have been commonly used in the industry.

RH testing is superior to surface-only testing in that it reflects the final RH conditions underneath an installed floor. Supplied with accurate knowledge of a slab’s RH condition, the general contractor, and flooring installer will know whether to allow for more drying time to reach adhesive/flooring specifications or to choose a different flooring adhesive/flooring product which is compatible with the slab’s current conditions. RH testing is a great benefit to the construction process, giving everyone involved the information they need to understand that it’s time to either wait or move on to the flooring installation phase of the project.

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Jason Spangler

Jason has 20+ years' experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

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