Moisture-related flooring and coating problems are one of the most serious and costly of construction-related issues being faced by owners, contractors, design professionals, installers and manufacturers. Each year, hundreds of millions of dollars are being spent to correct such problems and deal with the legal disputes that follow.

Conventional concrete slab mixtures always contain more water than the concrete hydration process actually requires. This “water of convenience” or “free water” is necessary to create a mixture that can be satisfactorily pumped, placed, screeded and finished. Some of this free water leaves the slab during the bleeding process, but further loss of moisture takes place as the slab dries over time. If an adequate vapor retarder/ barrier lies directly beneath a slab on ground, eventually the slab becomes dry enough for safe installation of flooring materials.

Concrete slabs initially possess an internal relative humidity (RH) of 100% from top to bottom. As the slab dries from the top down, assuming it is a slab on the ground with a vapor barrier, the RH at the top of the slab becomes less than at the bottom. However, if an impermeable covering is installed on top of the concrete, all drying stops and the moisture in the slab redistributes. The RH will be the same from top to bottom, only it will now be less than 100% depending on how much drying has taken place.

Because most floor coverings and adhesives are sensitive to moisture, and moisture-induced high pH levels, the moisture level in the slab must be accurately determined to be at or below the specific moisture levels required by the flooring or adhesive manufacturer. This step must not be avoided, or a total failure of the flooring could result.

When a flooring failure occurs, one aspect of the process that is scrutinized is the moisture testing that was performed prior to the installation. Questions will arise, such as: Who performed the tests? What methods and equipment were used? How were the test sites prepared? Under what conditions were the tests performed? How many tests were performed? Was the equipment properly calibrated? These queries are only the beginning of the scrutiny those who performed the tests will find themselves under. In all too many cases, the results of the moisture tests are discredited due to procedural errors on the part of those who performed the tests.

Certification is crucial to avoid these common mistakes. To improve the quality, and consistency of concrete slab moisture testing, the International Concrete Repair Institute (ICRI) has developed its Slab Moisture Testing Technician Certification Program. The purpose of this program is to help standardize the performance of existing American Society of Testing and Materials (ASTM) standards relating to moisture and PH testing, and provide more consistent, accurate and truly representative test results that will allow those responsible to make better decisions as to when a concrete floor is ready for a floor covering.

The ICRI certification program has two tiers. Tier 1 is educational only and is intended for those who are not regularly engaged in moisture testing yet have an active interest in learning more about how and why moisture testing is performed. The Tier 1 program consists of three hours of classroom training and a written exam. Likely candidates for Tier 1 would be owners, contractors, project managers, salespeople, manufacturers and specifications writers.

Tier 2 is a full certification program where applicants not only take the three-hour Tier 1 instructional course and must pass the written exam, but they also have to perform each of the four testing procedures taught in the classroom under the watchful eye of a qualified judge. The prerequisite for acceptance into the full certification Tier 2 program is previous testing experience.

Both the written exam and the performance tests are based on the following four ASTM standards, including all Annexes and Appendixes: ASTM F710 Preparing Concrete Floors to Receive Resilient Flooring; ASTM F1869 Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride; ASTM F2170 Determining Relative Humidity in Concrete Floor Slabs Using In-Situ Probes; and ASTM F2420 Determining Relative Humidity on the Surface of Concrete Floor Slabs Using Relative Humidity Probe Measurement and Insulated Hood.

Formal training through the ICRI certification program not only helps those who perform moisture testing better understand how the tests are to be performed, but the course also explains the science behind the test methods.  Project specifications around the country are beginning to require ICRI certification as it provides those who specify, or retain testing services a greater level of confidence that the test results they are reviewing have been determined properly.

The course is conducted annually in the spring and fall at various locations around the country, including the World of Concrete exhibition in Las Vegas. For more specific information on the program and to register, please go to and click on the Certification tab.

ICRI also offers this certification as an in-house program to companies that have 20 to 30 of their own staff who would like to get certified.  For more information on this type of arrangement or if you have questions regarding this certification program, please contact Mark Hughes, ICRI Technical Director, at (847) 827-0830 or by e-mail at


Peter Craig is an independent Concrete Floor Specialist with Concrete Constructives. He has over 37 years of experience with specialized aspects of concrete floor construction, maintenance, repair and protection. He also has experience with over 300 moisture related flooring issues nationwide. Craig is an active member of the International Concrete Repair Institute (ICRI) and was president of the Institute in 1996.