Evolution of moisture mitigation in concrete flooring

June 30, 2021

By Heather (Yario) Rice 

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Photos courtesy Maxxon

Whether for new construction or renovation, proper subfloor preparation is essential for executing a quality floor installation while extending the life of the flooring. In the last 20 to 30 years, regulations on volatile organic compounds (VOCs) have made buildings safer for occupants; however, these regulations have created new challenges for general contractors, as in the case of moisture vapor related flooring failures.

As the industry’s understanding of moisture emissions has grown, so have the types of solutions used to mitigate the problem. Today, a new category of moisture barriers makes it easier and more cost-effective than ever to properly prepare concrete and protect flooring.

The South Coast Air Quality Management District (SCAQMD) 1168, Adhesive and Sealant Applications was passed in 1989, limiting the amount of VOCs in adhesives, primers, and sealants. Removing solvents from adhesives made them VOC compliant; however, the resulting products were sensitive to moisture vapor in a way the industry has not seen before.

In the author’s observations, prior to the adoption of VOC regulations, moisture-related failures were largely unheard of. They noticed flooring failures began to occur with frequency in the early 2000s. The flooring industry quickly learned moisture vapor emissions were to blame, and they were not only common, but they could result from a wide variety of sources. Slabs, especially on grade, can vary in moisture content. From ground water intrusion to major weather events, the amount of moisture present could vary throughout the slab, increasing and decreasing throughout the life of the building. Slabs that tested with low moisture emissions could still have a failure weeks, months, or years down the road.

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Anhydrous Calcium Chloride (CaCl) test for ASTM F1869 to Measure Moisture Vapor Emission Rate of concrete sub-floor

Common construction practices also held the potential to cause moisture issues. The process of burning or hard troweling a slab was used to achieve floor flatness but had the secondary effect of sealing the surface. The application of a cure-and-seal expedited the curing process and sealed the surface to protect it from trade damage. When it came time to install flooring, manufacturers would require the surface of the slab be opened to ensure removal of bond breakers.

Because both processes trapped moisture in the slab, opening the surface allowed water vapor to exit as the relative humidity (RH) of the slab sought equilibrium with the ambient conditions on the jobsite. Not only did this cause condensation to form at the bond of the adhesive to the slab, it also could pull alkalinity from within the slab to the surface, creating a high pH environment.  Standard adhesives could handle a pH of up to nine while a freshly opened slab could easily reach a pH of 11 in a short timeframe.

Below the flooring, one of two things would happen: either the adhesive would not dry or adhesive that was dry when the flooring was installed would emulsify. This is where mold, mildew, and other aggravating floor failures would start. As with any emerging issue, preliminary testing and solutions needed to be developed before improvement was possible.

Testing methods and their shortcomings

CaCl test in progress on the job site.

The original method used to test for moisture vapor emissions was ASTM F1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride (CaCl). The CaCl test was performed on a mechanically prepared, porous surface. A petri dish containing CaCl salt crystals would be weighed and recorded, then placed on the prepared floor and sealed with a 609 x 609 mm (18 x 18 in.) housing unit. After 72 hours (newer versions of the test have reduced the waiting time to 24 to 72 hours), the petri dish was weighed again, and the moisture vapor emissions rate (MVER) was calculated using the change in mass for a given area over 72 hours. The resulting MVER was reported in pounds per 93 m2 (1000 sf) for a 24-hour period. It was this test that all flooring manufacturers initially adopted into their literature; the typical standard with a reading in excess of 1.4 kg (3 lbs) to 2.3 kg (5 lbs) per 93 m2 per 24 hours would require a moisture mitigation system.

As flooring contractors started realizing testing was the only way to prevent floor failures from coming back to haunt them, testing began to ramp up. The problem was the test was rarely performed to the standard, falsely signaling moisture emissions as being less of a problem than they were. Early testing, dependent on the project, was performed by flooring installers and general contractors, well-intentioned but untrained in the technical nuance of moisture vapor emissions and the method. ASTM F1869 required the units be placed at a frequency of three units in the first 93 m2 area and one additional unit placed in every subsequent 93 m2 area. Once in place, the units were to be left undisturbed for the duration of the test. Rarely was an adequate number of units placed, and in many cases, there were grossly fewer than required, i.e. four units in a 4645.2 m2 (50,000-sf) project instead of the required 52 units. On many early projects, the housing units were tampered with, damaged, or ignored, and were subject to construction traffic e.g. rolled over with scissor lifts, etc., which also lead to inaccurate results. The resulting failures highlighted the importance of strict adherence to the testing method and led to the growth of third-party certified testing consultants, which has greatly improved confidence in results.

Then, something new happened. Floors that tested below the flooring manufacturers specified emission rate were still experiencing failures that appeared to be related to moisture.  How could this be? ASTM F1869 only revealed moisture issues in the top 6.35 mm (0.25 in.) of the concrete slab and did not account for local temperatures and humidity. It also told nothing about what was happening inside the slab. A vapor retarder helps for on grade, if penetrated it could be a source of slab water, but moisture issues happen above grade, as well.

What’s occurring inside the slab?

The need to understand what was happening deeper in the slab drove the creation of ASTM F2170, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes. ASTM F2170 measures the relative humidity (RH) of a slab by drilling a hole to either 20 or 40 percent of the concrete slab depth, sealing the hole for 72 hours to allow moisture equilibrium to be achieved, and then inserting a probe to measure the RH as a percentage. Most flooring manufacturers have adopted this method as an accepted alternative to ASTM F1869 and will require a moisture mitigation system for slabs with greater than 80 percent RH. Using either method before flooring installation still did nothing to prevent changes in slab moisture from impacting the flooring.

A reliable method for mitigating moisture emissions became widely adopted in the early 2000s. A membrane-forming two-part epoxy installed over the concrete was installed to block moisture vapor emissions. The process required the concrete slab be shotblast to a concrete surface profile (CSP) of three to five, depending on the epoxy manufacturer’s guidelines. The opened slab would be left for 24 hours to allow off-gassing or pH changes to occur. The two parts of the epoxy were then blended, initiating the rolled in one or two coats. Following the epoxy installation, either sand was broadcast into the wet epoxy or a primer was installed over the hardened epoxy to facilitate bonding with the underlayment cap or flooring material. The original cost of these systems was $9 to $12 per square foot. Today, this system is installed for about $4 to $7 per square foot, which is still a costly prospect when many flooring finishes are $1 to $2 per square foot.

Preemptive moisture mitigation

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Dome over a CaCl test.

Preemptive moisture mitigation has become commonplace in hospital settings because a flooring failure resulting in downtime is far more costly than the price of moisture mitigation as an insurance policy. While this practice is extremely effective, it has not been widely adopted across commercial construction because adding $4 to $7 per square foot to the overall budget is not an option. Instead, contractors install the slab, wait as long as possible to test it and then deal with the problem if testing reveals an issue.

Therefore, moisture mitigation has had to evolve and improve. Owners were shocked to hear fixing their floors would cost more than the finish they had selected for them. Floor prep and flooring manufacturers started releasing products which did not require mitigation or testing. While many of these products work, they do not address the underlying moisture issue, which will remain a necessary consideration for every future flooring change. When it comes to moisture, it is generally accepted across the industry that it is best to fix the problem, thus floor prep manufacturers began exploring more cost-effective moisture mitigation technologies. Sodium silicates hit the scene as a solution for moisture emissions about 10 years ago. Sodium silicates are added to the concrete at the batch plant or onsite as the concrete pour is happening. These products have worked in certain settings, but overall have had mediocre success due to potential bond issues. Many flooring manufacturers do not recommend them underneath products. As such, their warranties generally require the presence of someone onsite to make sure their product is installed properly to prevent a moisture or bond failure.

Single-component mitigation technology

Single-component mitigation technology has been an area of advancement driven by excessive cost associated with the installation of a two-part epoxy moisture mitigation system. While some of these products have proven to perform as well as two-part epoxies, there has been pushback from architects and general contractors who are looking to adhere to ASTM F3010, Standard Practice for Two-Component Resin Based Membrane Forming Moisture Mitigation Systems for Use Under Resilient Floor Coverings. ASTM committees create several different types of documents, such as testing methods or practices for the industry. Standard test methods are procedures that generate test results defined to provide a uniform method for collecting specific data. ASTM F3010 is often perceived as a standard test method, however it is a standard practice, which is a set of instructions that does not generate a test result.

ASTM F3010, however, references ASTM E96, Standard Test Methods for Water Vapor Transmission of Materials. This standard test method is the key to ensuring a system can block moisture vapor emissions, and it is used across a variety of industries to test a broad range of products including moisture mitigation systems, tape, food, and pharmaceutical packaging.

The major advantage of a one-component product is its price advantage. A one-component product can be installed for several dollars less per square foot than a two-part epoxy system. Single-component moisture barriers generally only require an open surface to be installed. Instead of an aggressive CSP three to five, achieved through shotblasting, proper surface preparation can be achieved through the less intensive process of grinding. Single components are installed in two coats. However, the second coat also serves as the primer for the underlayment or flooring, which eliminates the need for an additional primer or sand broadcast. Because a single component is not activated by a chemical reaction as with a two-part epoxy, the installation process is more forgiving.

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Application of a single-component moisture barrier.

Moving forward

With reliable, cost-effective moisture mitigation solutions now available, some general contractors are realizing the extent of the benefits a moisture mitigation system has on projects, primary of which is the opportunity to reduce the construction timeline. The drying process in concrete starts the day the building is enclosed, and the HVAC starts running. Until this happens, the slab is subjected to water intrusion through weather conditions, water from other trades, etc. Once true drying conditions are achieved, the concrete will dry at a rate of 25.4 mm (1 in.) per month, so an 203.2 mm (8 in.) slab will take eight months to dry in optimal conditions. By installing a moisture mitigation system over green concrete, contractors are no longer beholden to the moisture content of the slab when scheduling flooring installation.

Developers are buying into these solutions because of the reduction in risk they represent. A cost-effective moisture mitigation system helps to avoid major budget impacts, timeline delays and the risk of litigation associated with unforeseen moisture problems. It is always easier to take care of a problem on the front end as construction will not have to stopped and the floor cleared to address the issue, which can take upwards of a week to resolve. The time impact alone pays for some of these newer one-component solutions.

Many products being developed in the finish world are no longer moisture sensitive. These are great alternatives, but as the problem is not addressed, the issue will need to be revisited when the floor covering is changed. Mold, mildew, finish and/or joint filler discoloration are also issues. With the introduction of reliable, affordable moisture mitigation solutions, it is possible to rethink the construction schedule and leverage a moisture barrier to reduce timelines and risk. Correcting the problem from the beginning may prove to be the best insurance policy that money can buy.

Endnotes:
  1. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2022/06/Concrete-Floor_OPENER.jpg
  2. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2022/06/Weights-before-and-after-the-Cacl-Test.jpg
  3. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2021/09/Dome-over-Cacl-Test.jpg
  4. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2021/09/Moisture-Barrier-Maxxon-MVP-One-Primer.jpg

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