Moisture Testing in Concrete Slabs Critical to Flooring Installation
One of the most important aspects of a commercial flooring installation is testing the moisture content in slabs prior to installing the flooring. This testing is necessary to ensure that moisture levels in the slabs at the time of the flooring installation comply with the flooring manufacturer’s requirements, which differ from product to product and manufacturer to manufacturer.
Moisture in slabs can come from a variety of sources. In some cases, newly poured slabs are not given sufficient time to dry by contractors faced with tight deadlines for project completion. Older slabs may have been damaged during construction, allowing moisture to settle in them. Moisture barriers may have been compromised over time – or perhaps never used at all, which is often the case in older buildings – allowing ground water to migrate up through the slab.
Moisture in Slabs: A Costly Proposition
Whatever the source of the moisture, one thing is certain. Flooring installed over a slab that contains a high moisture vapor emission rate (MVER) is likely to bubble, discolor, de-bond or have moisture coming through the seams or joints of the flooring. This almost universally results in costly remediation, dissatisfied end users and a black eye for the installation contractor and the flooring industry as a whole.
What exactly are the financial costs? Some industry analysts say that remediating failed flooring installations caused by high moisture content in slabs costs building owners, general contractors, flooring installers and others more than $500 million annually.
In today’s litigious society, it is important to remember that, unless contractually excluded from responsibility, the liability for a failed flooring installation will transfer to the flooring contractor if moisture or other issues with the slab lead to a failed flooring installation. Simply put, the person who covers a slab with a flooring product is responsible for the work, even if the installer was pressured by the project manager or others to forego moisture testing, or ignore the results altogether, due to time or budget constraints. This puts a premium on accurate moisture testing, using commonly-accepted methods and documented results by the flooring contractor.
Moisture testing has come a long way from the days when the method of choice was taping down plastic or non-porous backed mats on a slab to see if any moisture surfaced. Two pivotal improvements were the widely used ASTM 1869 calcium chloride test, which tests moisture migration through the top one-third of the slab, and ASTM 2170 test, which tests for moisture deeper into the slab.
More recently, a number of new technologies have been introduced to further enhance the state-of-the-art of moisture testing. Among the most noteworthy are relative humidity probes that significantly decrease the time it takes to conduct moisture testing, an exceedingly important feature in today’s era of fast-track construction.
Five Critical Questions
Given that the stakes are high, the importance of accurate moisture testing of slabs cannot be understated. There are a number of variables that can affect MVER readings and answers to these five questions are critical in understanding which might be in play:
Is there a moisture barrier under the slab and what is its condition? With older slabs, it is common to find compromised moisture barriers or no moisture barrier at all. When this is the case, MVER levels can rise or fall as moisture evaporates from the slab and is then reintroduced, depending on changing climatic conditions. Conversely, newer slabs, which are typically tested a few weeks prior to the flooring installation date, are required to have a moisture barrier under them. If the barrier is not compromised, MVER levels should consistently drop over a testing period. If moisture levels are high, it is a strong signal that using a moisture mitigation system prior to the flooring installation may be necessary.
What is the depth of the slab? Most manufacturers of flooring products require more stringent moisture testing today than they have in the past. Their concern is not only about moisture on the surface of the slab, but also deeper into it. As a result, the ASTM 2170 moisture test requires in situ testing probes to be set at a depth of 40 percent of the thickness of the slab. For example, in a 6” slab, the probes would be set at a depth of 2.5” to test moisture levels inside the slab.
Does the slab contain curing compounds? Curing compounds are used in new slabs to slow the evaporation of the water, enabling the slab to gain strength faster. When this is the case, MVER readings will remain higher longer. In addition, some curing compounds are not approved by flooring manufacturers and need to be mechanically removed before the installation takes place.
Is the building climatized when the moisture testing is conducted? More often than not with new construction, HVAC is not operational prior to or at the time of the moisture testing. This will affect test results, slowing the rate of decline in moisture readings. In order to accurately test the moisture in the slab, the ambient temperature must reflect the building’s normal operating conditions. Whether performing the ASTM 1869 or ASTM 2170 test, both require that the space where the flooring installation will take place must have an operational HVAC system when the moisture tests are conducted.
How was the slab constructed? Some slabs are poured under roof and others are poured before the walls and roof are put in place. In the latter case, there is a high probability that the slab will have been subjected to direct sun, rain and wide temperature swings during the curing process. All of these conditions will affect moisture levels in the slab.
End-User is Beneficiary
Accurate moisture testing is often not only a necessary first step in a flooring installation, but it is the foundation on which the success of the entire installation rests. The ultimate beneficiary of accurate test results is not the general contractor, the building owner or even the flooring manufacturer—it’s the end user, whose repeat business should be the goal of everyone involved in the flooring industry.