ASTM F1869 - Calcium Chloride Moisture Test

Understanding Calcium Chloride Testing for Concrete Moisture

When installing floor coverings on concrete slabs, it is crucial to ensure that the concrete is dry enough to avoid moisture-related problems in the future. One way of determining the moisture level of concrete is through the use of calcium chloride (CaCl) moisture testing. This method has been in use since the early 1940s and has gained industry acceptance as a practical standard.

What is CaCl Moisture Testing?

The CaCl moisture test measures the moisture vapor emission rate (MVER) of concrete slabs. It determines the quantitative indication of how many pounds of slab moisture evaporated from 1000 square feet of concrete over a 24-hour period. The applicable industry standard for this test is ASTM F1869, which covers the quantitative determination of the rate of moisture vapor emitted from below-grade, on-grade, and above-grade (suspended) bare concrete floors.

Limitations of CaCl Testing

While CaCl testing is widely used, it has several limitations that have been discovered over time. One of the main issues with this method is that it only measures moisture at the surface of the concrete slab, typically the top one-half to three-quarters of an inch. This does not account for moisture conditions deeper in the slab where the natural migration process of concrete moisture drying occurs.

Another problem with CaCl testing is that it tends to underestimate the true moisture conditions at the high end of the moisture spectrum and overestimate the moisture conditions of older slabs. This can lead to erroneous decisions about whether a concrete slab is ready for flooring installation.

Additionally, CaCl testing does not account for concentrated concrete moisture residing at a greater depth than what is measured by the test. When this moisture reaches a covered concrete surface, it cannot evaporate, leading to continued moisture problems.

Alternatives to CaCl Testing

In response to the limitations of CaCl testing, the American Society for Testing and Materials made two changes to moisture measurement industry standards. Firstly, it amended ASTM F1869 to remove the CaCl moisture test as a means of measuring lightweight concrete moisture. Secondly, ASTM created F2170, a new standard that recognized in situ RH testing as an integral assessment method.

In situ RH testing involves inserting a probe into a concrete slab and measuring the relative humidity at the depth of the probe. This method provides a more accurate assessment of concrete moisture levels and can help avoid moisture-related flooring problems.

Conclusion

While CaCl moisture testing has a long history in the concrete flooring industry, it has several limitations that can lead to moisture-related problems in the future. As such, alternative methods, such as in situ RH testing, should be considered to ensure accurate and reliable moisture assessments.

Calcium Chloride Testing Disallowed for Lightweight Concrete: The Move to ASTM F2170 In Situ Relative Humidity (RH) Testing

For decades, calcium chloride (CaCl) testing has been used to determine the suitable moisture content of poured concrete slabs when applying resilient floor coverings. The standard for performing the CaCl test has seen many changes over the years, but its reliability has always been a concern. As continued testing confirmed its inadequacies, the ASTM F1869 standard for using CaCl was changed in 2010 to specifically disallow CaCl testing for all lightweight aggregate concrete.

This article discusses the evolution of concrete moisture testing and why in situ RH testing, according to ASTM F2170, has for a number of years now been replacing CaCl as the preferred method for concrete moisture determination.

History of Calcium Chloride Testing

The first known published information on CaCl testing for concrete was by Armstrong in the 1940s as a “go or no go” type of test. It was used with no numerical assessment resulting from the test. There is also no record of the science behind the decision to use anhydrous CaCl instead of another desiccant. Regardless, it went into use as a method of testing concrete readiness for linoleum application.

When Kentile began to sell CaCl test kits in the 1960s, measuring the weight of the salt before and after exposure to vapor emissions from concrete became the recommended practice. This method is also known as a moisture vapor emission rate (MVER) test. However, scientific record at that time did not support the target range of numbers given with the test as being suitable for flooring installation conditions. And inherent to CaCl testing, uncertainties occurred due to varying ambient environmental conditions, varying concrete mixtures, and various admixtures.

Problems with Calcium Chloride Testing

In the 1990s, testing performed by Howard Kanare's team at CTLGroup showed several problems with the ASTM F1869 standard for CaCl testing. The most serious problem with the CaCl test is that at the higher end of moisture conditions, where there is the most danger of floor covering failures, CaCl testing following the ASTM F1869 standard can underestimate the true moisture condition. A much less serious phenomenon is the overestimation of the moisture conditions in very old slabs that are not actually emitting any net moisture vapor. Added to their findings was the observation that a CaCl test only measures the top ½ – ¾ inch of the slab, while typically higher concentrations of moisture reside deeper in the slab and migrate to the surface after applying a floor covering. The conclusion of their testing was that CaCl testing was fundamentally unreliable for predicting the performance of resilient floor coverings over concrete.

In Situ RH Testing as an Alternative

Since 2002, ASTM F2170 In Situ Relative Humidity (RH) testing has been replacing CaCl as the preferred method for concrete moisture determination. RH testing has proven to be more user-friendly, accurate, and cost-efficient than CaCl testing. In situ RH testing is also more appropriate to the resilient floor covering industry.

During the 1990s, Goran Hedenblad began researching the characteristics of concrete moisture through the Swedish Council of Research. Hedenblad performed experiments that identified moisture gradients in a slab from the exposed surface to deeper into a slab. Further testing indicated that after a slab was covered, the moisture re-distributed to equalize to a constant moisture concentration throughout the slab. Final indications showed that after the slab was covered, the surface presented a higher moisture concentration to the floor covering after this equalization process.