Every year, in North America alone, commercial property owners spend an estimated $2.4 billion on remediation of structures and floor coverings due to moisture-related failures. Excessive moisture in concrete slabs is not only the most commonly recurring flooring problem in all types of commercial, industrial, and residential buildings—it is the most expensive. Moreover, when you consider the added financial burden of business disruptions and loss of return customers, the economic impact of finished flooring damage can be staggering.
Resilient floor covering especially is prone to failure due to excess water vapor emissions from concrete. Moisture can cause the adhesive between the flooring material and the concrete to break down, causing the flooring to debond or blister. It also can create a favorable environment for mold and mildew growth, which can cause a host of health problems.
There are several steps building owners, specifiers, and contractors can take to reduce costly moisture-related flooring failures. These include advanced planning, preconstruction quality control, ensuring specifications and manufacturer’s installation instructions align, and knowing when to ask for help from a professional. If moisture issues are identified and addressed before work begins, corrective measures are less disruptive and expensive compared to remediation after the floor covering is installed.
Water, as an essential ingredient in concrete to promote cement hydration, is important for achieving a properly made concrete slab. However, free water (i.e., leftover water after cement hydration) can create problems for the floor finishes if they are moisture sensitive. On average, a slab on grade typically requires one month per inch of concrete depth for the surface to properly dry for normal weight concrete. This will vary based on ambient site conditions. Lightweight concrete, mostly used on elevated slabs, however, can require twice as much drying time or more due to the saturation of the lightweight aggregates used in the concrete mix design.
An observation opening at a blister location in Epoxy Terrazzo (circled)
External sources of water also greatly impact moisture conditions. Problems can arise from a lack of moisture barriers and vapor retarders under the slab, inadequate grading preventing drainage of rainwater away from the of the slab, plumbing leaks, sewer backups, and faulty sprinkler systems to name a few. Ambient conditions also play a role in the drying of concrete slabs.
Floor Covering Moisture Sensitivities
Today’s more environmentally friendly adhesives, grouts, and flooring materials are more moisture sensitive than ever before, and manufacturers have established moisture tolerance levels for each of their specific products. While the resilient flooring industry is starting to develop materials that are more resistant to high levels of moisture, these commercial offerings can be significantly more expensive than value-engineered flooring products.
Newer low-VOC adhesives can be more susceptible to moisture-related deterioration than their solvent-based predecessors. Rubber backing on flooring can be especially problematic as moisture from the slab is trapped at the rubber backing and can re-emulsify the adhesive. Consequentially, resilient flooring can blister and debond/delaminate from the concrete substrate.
Grout used for tile floors is also not immune to problems with moisture vapor emission through concrete slabs, and its discoloration is often the first sign that there is an excess moisture issue. The moisture can eventually soften the grout, making it more prone to crumbling, or it can result in white powdery efflorescence. It can also cause expansion and warping of the tile, which can lead to delamination.
Wood flooring can be sensitive to concrete moisture.
Wood flooring is incredibly sensitive to moisture, and manufacturers often recommend installing a moisture barrier between the subfloor and a floating wood floor to prevent moisture intrusion. If the moisture barrier becomes compromised, moisture can cause swelling, warping, buckling, and discoloration of the finished wood flooring.
Mitigating Moisture Problems
There are many problems that can arise in the installation of flooring. When issues do occur, many failures are due to quality control situations—that is, something was overlooked on the front end and then needs to be fixed on the back end.
No one wants to spend a lot of time and money fixing issues after the fact. For this reason, many building owners engage a consultant during preconstruction planning. This type of proactive approach by a third party can involve the review of specifications, design drawings, and submitted materials to ensure that the flooring can be installed as designed. They can also make recommendations on concrete mix designs, guidance on slab placements and surface finishing techniques, managing optimal concrete curing practices, and monitoring concrete slab drying times.
Installation of a RH Probe. The relative humidity probe test (ASTM F-2170) measures relative humidity via moisture vapor emission.
Moisture issues can often be avoided by allowing the concrete slab to properly dry, under the right conditions. In today’s fast-track construction world, however, schedules often do not provide sufficient time for concrete to dry naturally. When this is the case, a consultant can provide invaluable assistance on the use of special products or processes to reduce the volume of moisture present or time needed to dry the slab, as well as the application of moisture suppression systems.
Moisture Testing Is a Critical Requirement
For many solid reasons, validation of moisture levels by a third-party certified testing technician is a common requirement in specifications and manufacturer’s instructions before the installation of flooring materials above a concrete slab. An independent testing company is not a stakeholder, but an important member of the team. Their certified experts provide unbiased results to help stakeholders avoid the risk of flooring failures.
There are two common methods for testing moisture in concrete.
The relative humidity probe test (ASTM F-2170). This standardized test uses in-situ probes to obtain a gradient of the slab moisture when drilled down to a depth of 40% of the slab thickness. It is the most reliable method currently available for measuring relative humidity via moisture vapor emission and can be used to take multiple measurements to assess changes over time.
The calcium chloride test (ASTM F-1869). This test measures moisture by placing a dish of calcium chloride on the concrete and sealing it under a pre-defined area dome. It only measures moisture in the top one inch of the surface and cannot be used to test lightweight concrete.
How CTLGroup Can Help
Moisture issues in concrete slabs can be costly if installed resilient flooring fails. Whether your flooring system is in a healthcare facility, warehouse, retail store, or commercial building, CTLGroup can help you avoid problems by providing expert guidance and technical services throughout the phases of the project. If you are experiencing an existing floor problem, our team of materials scientists, engineers, and certified concrete moisture testing technicians will work together to determine its source and recommend practical, permanent solutions.
We are enthused, prepared, and well positioned to support your current and future flooring project needs. Contact us to learn more about our extensive construction/installation experience, troubleshooting expertise, and world-class materials testing capabilities.
About the Author:
Dean Adams is an associate at CTLGroup. Mr. Adams has been involved in a variety of projects for repair, remediation, and restoration, ranging from field evaluations, non- and semi-destructive testing, forensic investigations, and litigation support. Mr. Adams has vast experience with evaluation of materials that include concrete, mortar, grout, brick, concrete block, terrazzo, ceramic tile, resilient flooring covering, hardwood, self-leveling underlayment, and epoxy coating. Mr. Adams is a Member of the ASTM F06 Committee on Resilient Floor Coverings, a Certified Concrete Slab Moisture Testing Technician (CCSMTT), an ACI Concrete Field-Testing Technician, and a member of the National Tile Contractors Association (NTCA). Contact Mr. Adams at email@example.com.
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