- Communicate early. Establishing open lines of communication early is the most effective way to ensure the specifications listed in the previous point are adhered to consistently. When communicating with architects, be sure to include details on the following specifications: concrete ratios and mix; concrete finishes; curing compounds; and sub-slab vapor retarders. Additionally, ask for third-party certification for concrete testing (see related sidebar), as well as allowances or deductive alternates to be in bid for moisture mitigation if needed.
When working with flooring contractors, confirm in advance they either have testing included in their contract or let them know third-party testing is covered. Also, be sure to set a meeting with the concrete contractor prior to pouring to discuss whether a curing compound is necessary, the concrete mix and finish, as well as the sub-slab vapor retarder. If they are testing the floor, have them set RH probes months prior to scheduling. Calcium tests are a waste prior to proper conditioning as they don’t provide accurate readings, but probes will start to tell a story. If the potential of moisture mitigation is needed, have the contractor price earlier rather than later so the end user doesn’t feel stuck if they are not able to have “allowances” up front.
2. Renovation Slabs & Trenches
Now that we’ve covered new construction slabs, we’ll turn our attention to the second area of concern with concrete and moisture: renovation slabs and trenches. As any design or construction professionals knows, existing slabs can be (and often are) flawed. This may be the result of a number of factors, including the lack of an effective moisture vapor retarder or barrier; a degraded, broken down, or torn barrier; high ground water, irrigation, or drainage; or a high water-to-cement ratio, creating continuous interconnected pores—all of which contribute to flooring failures.
Contrary to popular belief, bonded existing flooring does not necessarily equate to the absence of moisture issues. Many existing floors are covered with the original layer having been installed with a solvent-based adhesive, increasing moisture levels in the floor. Also, existing materials are oftentimes more permeable than the new materials specified for installation.
Additionally, existing concrete slabs are characterized by continuous moisture vapor emissions. Moisture naturally occurring in the earth or added through irrigation and drainage is the most troublesome source in older buildings and can equally impact newer ones. In fact, the largest foundation of moisture transmission occurs when it is not properly inhibited from reaching the concrete slab. The reason this is so problematic is because moisture in a floor slab, which carries salts, always tries to equalize with moisture in the air above it. As salts are carried to a slab’s surface, it expands, causing the breakdown of adhesive bonds. Further, tree roots, poor landscaping, improper gutter and drainage systems, along with poor or no vapor retarder mixed with over-watered, highly porous concrete, create the “perfect storm” for an epic floor system failure.
The effects of excessive moisture vapor transmission (MVT) are many and can be very problematic at the floor surface. These negative outcomes include:
- Constant flow of moisture
- Alkaline salt migration
- Adhesive re-emulsification
- Trapped water collected under flooring
- Bond failure
- Mold and mildew
What Do You Do?
As is the case with new construction slabs, design and construction professionals should plan ahead to help eliminate or mitigate excess moisture in existing slabs before proceeding with flooring specification and installation plans. The following steps should be helpful in dealing with flawed renovation slabs:
- Learn the concrete history of the building. Check with the building owner or facility manger to confirm the placement of vapor retarder. All flooring products require a vapor retarder for warranty, so be sure to inquire about original concrete specification/submittals. Also, be sure to ask about previous floor coverings to find out the answers to questions such as:
- How many layers were installed?
- Were there any issues with floor failures?
- Were there maintenance issues that could not be resolved?
- Analyze building drainage, irrigation, and landscaping. If there is an existing gutter system in place on site, have a contractor or facility manager check to see if it is functional and effectively diverting water away from the building. A landscape architect should analyze the existing site to ensure that it is graded properly, that landscaping is semi-below grade areas, and that there are no areas of washed out soil or mulch. Finally, the skirt of the building should be inspected for soil or mulch build-up to or past weak holes, as well as for any signs of mildew.
- Test/analyze building interior. The first place to look for moisture issues in the concrete is obviously at the existing floor surface. Look for any signs of moisture (peaking seams, bubbles, hollowness, cracked or broken tiles) and take appropriate steps to locate and repair the problem. Keep an eye out for signs of moisture in other finishes as well, including chipped or peeling paint, sagging ceiling tiles, rusted doorframes, or moisture marks on wood base or behind cover bases.
- Test concrete. If you’re able, ask that an independent third-party conduct concrete testing according to ASTM standards (see related sidebar) prior to providing a quote for the project. If testing is not possible prior to the quote, make sure it is done as early in the project as possible, and absolutely prior to HVAC shutdown.
- Communicate early. When it comes to communicating with the architect or owner regarding existing concrete slabs, speak to the importance of effective sub-slab vapor retarders and/or lack thereof upfront. As noted above, also inquire about third-party testing prior to the bid or directly afterward (and if unable to discuss, clarify the bid offer). If possible, emphasize the importance of keeping the “service condition” during the renovation, and make allowances for moisture remediation.
With the flooring contractor, confirm that they either have testing included in the specifications or let them know third-party testing is covered, and plan a pre-bid meeting to specifically discuss how to avoid change orders, as the contractor may know about the conditions of the building from previous work. Also, develop plans based on the ability to test and on the logistics of the job with the owner and other trades involved.
Trenches: What Do You Do?
Trenches are an unavoidable problem that are typically not thought of as an issue and, therefore, are not planned for properly. Unfortunately, trenches can ruin a floor due to vapor emissions quickly because they are normally filled with a typical or slow-drying cement. Additionally, trenches are usually over-watered with “water of convenience” to ease workability—a scenario in which the concrete becomes too porous and creates a weak or laitance surface, resulting in a number of flooring failures previously identified.
As with new construction and renovation slabs, the key to successfully addressing moisture issues with trenches is essentially the same:
- Plan ahead and communicate. When filling a trench, make certain that it is done with the proper water-to-cement ratio; installed per concrete institute specifications, including proper vapor retarder, repaired vapor retarder, and/or bonding agent from new to existing concrete; and allow for required drying times. Additionally, if drying time is not allowed due to project constraints, request special pricing for use of fast-setting cement or use of two-part, 100-percent solid mitigation.
Finally, communicate with the flooring contractor about the quantity, time frame, and pricing as early as possible to avoid further costs and delays.
The Bottom Line
As we’ve seen, there are myriad problems associated with moisture and concrete in both new and existing buildings that can cause plenty of headaches, delays, and additional costs to projects. While the problem of persistent moisture in concrete that leads to flooring failure is a formidable one, it doesn’t have to be an unavoidable cost of doing business. With thoughtful consideration, planning, and execution, design and construction professionals can not only mitigate the effects of this common issue, but also develop more robust and reliable flooring specifications that will not only look great, but last a lifetime.
Protection Tests for Moisture in Concrete
In commercial building projects where flooring or impermeable membranes will be installed on top of a concrete slab, a test for excess moisture is a common requirement today—and for many good reasons, as this CEU has previously illustrated. However, “while several standard moisture test methods are available, no single test reveals everything that should be considered in deciding when flooring can be installed or a coating applied,” warned Tom Klemens in “Concrete Construction.” Further, Klemens said that the test used is only as good as the stability of the environmental conditions. In other words, they should represent the long-term conditions under which the building will be expected to perform.
The two most commonly used industry standards for testing the moisture level of concrete in new or existing slabs are ASTM F1869-16 and ASTM F-2170-16, both of which are detailed below:
- ASTM F1869-16: Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride. Extrapolated test data is reported as pounds of moisture vapor being emitted from the concrete subfloor over a 1,000-square-foot area during a 24-hour period. The subject building must be acclimated at or near the “service” temperature and relative humidity levels anticipated during occupancy or use.
Note: Some floor covering manufacturers no longer recognize calcium chloride test results for determining concrete dryness, however. This is due to the fact that the test only measures the top ¼ inch to ½ inch of the surface, giving potentially false readings as greater volume of moisture may be present at the floor covering/concrete interface after installation is completed than was originally anticipated. ASTM F 1869 specifically excludes calcium chloride tests from use on concrete containing lightweight aggregate and/or gypsum screeds.
- ASTM F-2170-16: Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in-situ Probes. This test method covers the quantitative determination of percent relative humidity in concrete slabs. The subject building must be acclimated at or near the “service” temperature and relative humidity levels anticipated during occupancy or use. This method provides more predictive test data, and test results appear to be less impacted by the type of—or lack of—floor coverings in place prior to testing. Testing performed with single-use probes has brought the cost down to a level comparable with calcium chloride-type tests. Some resilient flooring manufacturers exclusively require in-situ relative humidity testing, while others are listing it as the preferred test method.
While probes cannot give “certified” readings without meeting ambient service requirements, they can be put in early to monitor or watch the drying properties, allowing earlier action if concrete drying will not meet the project’s schedule.
Issued in 2002, the major advantage of the F-2170 method is that it allows for remote monitoring. “Once in place, the instruments can give continuous, instantaneous moisture readings at any depth in the concrete floor slab,” explained Howard Kanare, president at Koster American. “Because the new test method uses electronic sensors, data can be output to data loggers and transmitted from remote locations without requiring technicians onsite. Buildings can be monitored while floors are drying over a long period of time and the data can be used to predict when a floor will be ready to receive a moisture-sensitive finish.”
Who should provide testing?
Both the flooring contractor and general contractor have a vested interest in the test results. It is best to allow an independent, third-part- certified testing company to conduct the concrete assessment and offer the results. This keeps the general contractor and flooring contractor from looking like they just want a change order by separating their interests. As an added benefit, the owner is less likely to be upset with the construction team if failures, delays, or additional costs occur.
In fact, the Floor Covering Installation Contractors Association (FCICA) released an official position paper on not only the importance of moisture emission testing, but also on the governance of such a critical responsibility:
Changes within the construction industry continue to keep even the most dedicated flooring contractors in a constant struggle to install all kinds of flooring systems properly. Floor covering materials themselves are in a constant state of flux with new materials, backing and coatings being developed that often have an impact on the installation of these materials. Flooring adhesives are for the most part solvent free, meaning that more care is needed during flooring placement to ensure excess water from the adhesive has dissipated. High water/cement ratios that facilitate concrete placement and finishing, concrete with lightweight aggregate and concrete that dries from only one side mean longer drying times are required before flooring can be installed. This is in direct opposition to what the owners want; fast track construction. A construction schedule that was once a yearlong process is now compacted into a few months. Add to this the changes in the location of the vapor retarder, the increased use or lightweight aggregate, fly ash and admixtures in the concrete mix design, and it is clear that a more scientific approach is needed to clearly identify problems associated with substrate induced flooring failures.
With all the above referenced factors listed, it is unreasonable to expect a flooring installer to be responsible to correct concrete problems that they have had no role in creating. While they are continually encouraged to develop sufficient expertise to anticipate and ask the proper questions for evaluation of potential concrete/flooring problems, it is not their responsibility to correct problematic substrate conditions created by others.
Another factor is that the flooring contractor has a vested interest in ensuring the integrity of the substrate as being 100-percent suitable prior to beginning the flooring installation process. We know the adage, “Once you start installing, you own the floor.” For this reason, flooring contractors are often viewed as having a built-in agenda to get change orders for flatness and moisture mitigation that are naturally resisted by the general contractor, owner, and/or architect.
An independent testing company has no such agenda; it tests the substrate and reports the results. Decisions can then be based on unbiased test results. General contractors and flooring contractors must be made aware of all of the test results. Most flooring manufacturers have specific test criteria and limits required for the moisture conditions of concrete. The flooring contractor should only commence installation once these requirements are met and should not begin flooring installation if any requirement is outside of the manufacturer recommended limits.
FCICA recommends that one of the best ways to ensure fair and responsible testing is to specify that it be done by a third-party independent and/or certified testing company. Their results are clear and unbiased. The project can then proceed in accordance with the findings.
Counting the Costs: Moisture-related Problems in Buildings
As mentioned at the onset of this CEU, the presence of excess moisture in buildings can be a costly undertaking to address and can have negative impacts on occupant health. As a result, moisture control is fundamental to the proper functioning of any building.
According to the U.S. Environmental Protection Agency (EPA) controlling moisture is important to protect occupants from adverse health effects and to protect the building, its mechanical systems, and its contents from physical or chemical damage. Yet, moisture problems are so common in buildings, many people consider them inevitable.
Many common moisture problems can be traced to poor decisions in design, construction, or maintenance. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) notes that, more often than not, the more serious problems are caused by decisions made by members of any of a number of different professions. However, such problems can be avoided with techniques that are based on a solid understanding of how water behaves in buildings. Moisture control consists of:
- Preventing water intrusion and condensation in areas of a building that must remain dry.
- Limiting the areas of a building that are routinely wet because of their use (e.g., bathrooms, spas, kitchens and janitorial closets) and drying them out when they do get wet.
To be successful, moisture control does not require everything be kept completely dry. Moisture control is adequate as long as vulnerable materials are kept dry enough to avoid problems. That means the building must be designed, constructed, and operated so that vulnerable materials do not get wet. It also means that when materials do get wet, the building needs to be managed in such a way that the damp materials dry out quickly.
Impacts of Moisture on Human Health
At the request of the U.S. Centers for Disease Control and Prevention (CDC), the Institute of Medicine (IOM) of the National Academy of Sciences convened a committee of experts to conduct a comprehensive review of the scientific literature concerning the relationship between damp or moldy indoor environments and the appearance of adverse health effects in exposed populations. Based on their review, the members of the Committee on Damp Indoor Spaces and Health concluded that the epidemiologic evidence shows an association between exposure to damp indoor environments and adverse health effects, including:
- Upper respiratory (nasal and throat) symptoms
- Asthma symptoms in sensitized persons with asthma
The committee also determined that there is limited or suggestive evidence of an association between exposure to damp indoor environments and:
- Dyspnea (shortness of breath)
- Lower respiratory illness in otherwise healthy children
- Asthma development
Details of the results of this review were published in a 2004 report, Damp Indoor Spaces and Health. It is also important to note that immuno-compromised individuals, such as some categories of hospital patients, are at increased risk for fungal colonization and opportunistic infections. After the publication of the IOM report, a study by Lawrence Berkeley National Laboratory concluded that building dampness and mold raise the risk of a variety of respiratory and asthma-related health effects by 30 to 50 percent. A companion study by EPA and Berkeley Lab estimated that 4.6 million cases of asthma (or 21 percent of all asthma cases in the U.S.) could be attributed to exposure to dampness and mold in homes.
Damage Caused by Moisture
In addition to causing health problems, moisture can damage building materials and components. For example:
- Prolonged damp conditions can lead to the colonization of building materials and HVAC systems by molds, bacteria, wood-decaying molds, and insect pests (e.g., termites and carpenter ants).
- Chemical reactions with building materials and components can cause, for example, structural fasteners, wiring, metal roofing, and conditioning coils to corrode and flooring or roofing adhesives to fail.
- Water-soluble building materials (e.g., gypsum board) can return to solution.
- Wooden materials can warp, swell, or rot.
- Brick or concrete can be damaged during freeze/thaw cycles and by sub-surface salt deposition.
- Paints and varnishes can be damaged.
- The insulating value (R-value) of thermal insulation can be reduced.
The High Costs of Moisture Problems
Health problems and building damage due to moisture can be extremely expensive. Berkeley Lab estimates that the annual asthma-related medical costs attributable to exposures to dampness and mold total approximately $3.5 billion in the U.S. But many more adverse health outcomes due to damp buildings have been reported, each with associated costs of its own. And damage to the building itself is also costly. Building owners and tenants bear a significant proportion of these costs, including:
- Absenteeism due to illnesses such as asthma.
- Reduced productivity due to moisture-related health and comfort problems.
- Increased insurance risk, repair and replacement costs associated with corroded structural fasteners, wiring and damaged moisture-sensitive materials.
- Repair and replacement costs associated with damaged furniture, products, and supplies.
- Loss of use of building spaces after damage and during repairs.
- Increased insurance and litigation costs related to moisture damage claims.
Source: U.S. EPA
ASTM F 1869, “Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride,” (2016), ASTM International
ASTM F2170-16a, “Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes,” (2016), ASTM International
ACI 302.1R, “Guide to Concrete Floor and Slab Construction,” (2015), American Concrete Institute
ACI 303.2R, “Guide for Concrete Slabs That Receive Moisture-Sensitive Flooring Materials,” (2015), American Concrete Institute
ACI 308R-16, “Guide to External Curing of Concrete,” (2016), American Concrete Institute
Brewer, H.W., “Moisture Migration – Concrete Slab-on-Ground Construction,” (1964), Journal of the PCA Research and Development Laboratories, Vol. 7, Num. 2
Building Research Institute, “Effectiveness of Concrete Admixtures in Controlling Transmission of Moisture Through Slabs-on-Ground: A Report of the Building Research Advisory Board to the Federal Housing Administration,” (1958), University of Michigan Libraries, National Academy of Sciences- National Research Council, Publication 596
“Concrete Moisture Testing,” (2013), Flooring Contractors Association
Dolen, T. P., “Historical Development of Durable Concrete for the Bureau of Reclamation,” (2008) U.S. Department of the Interior
“Moisture Emission Testing – Responsibility and Qualifications for Testing,” (2001), World Floor Covering Association
Smith, R., “Don’t Power Trowel Blindly and Trap Unwanted Concrete Moisture,” (2014), RHSPEC
Spangler, J., “Moisture Related Flooring Failure: How Bad Can It Be?” (April 24, 2013), Wagner Meters
Zemajtis, J. Z., “Role of Concrete Curing,” (2011), Portland Cement Association