Understanding ASTM E 96 and Moisture in Concrete
by Jim Essig - Technical Director
There are many misnomers when it comes to truly understanding the moisture content of concrete slabs and the movement of moisture vapor through the slab. Conducting due diligence with testing is vital, especially since the testing processes can vary greatly. It’s critically important to understand the meaning behind the test results – and what the test isn’t telling you.
What is ASTM E 96?
ASTM E 96 Standard Test Method for Water Vapor Transmission (WVT) of Materials is often mistakenly called out when talking about moisture content of concrete floors. Most people don’t realize that this test method does not measure moisture content of concrete floors. Similarly, it cannot be performed in the field or on-site.
In reality, ASTM E 96 is simply a laboratory test that determines the water vapor transmission rate of materials, be it packaging materials, building vapor barriers and vapor retarders, or in the case of flooring, membrane forming moisture mitigation systems. The test can be run by both a Desiccant method, where water vapor transmits into a test dish, and a Water method, where water vapor transmits out of the test dish.
A Deeper Look at Moisture Testing
APF takes a scientific approach to testing moisture vapor transmission rates of polymeric coatings applied to concrete floors to ensure an accurate, standardized result.
A concrete specimen is coated at the recommended coverage rate with the material to be tested and cured for seven days. Then, the coated concrete specimen is sealed into a custom-designed test apparatus with water in the bottom, and then placed into an environmental chamber maintained at 78°F (25°C) and 50% relative humidity. This creates a high humidity environment under the coated concrete panel to force vapor drive through the coated panel into the lower humidity chamber environment. The apparatus is repeatedly weighed over time, and the resulting weight loss of water is measured and plotted over time.
The International Residential Code (IRC) has classified vapor retarder materials as Class I, II and III. ASTM E 96 Desiccant method is used to determine the class of the vapor retarders. Class I having a perm rating of ≤ 0.1, Class II having a perm rating of >0.1 to <1.0, and Class III > 1.0 to 10 perm.
But it’s important to note that these classifications are for building materials, not flooring materials, although they are often mistakenly quoted.
The reality is that until recently there weren’t any specifications for the WVT of membrane-forming moisture mitigation systems. In general, the concrete flooring industry relies on field testing concrete substrates using ASTM F 1869 Measuring Moisture Vapor Emission Rates of Concrete Subfloor Using Anhydrous Calcium Chloride. The test reports the rate of moisture vapor emission measured in pounds of moisture over a 1,000-square-foot area during a 24-hour period. The industry has accepted that concrete showing a value of more than three pounds should not be coated with a non-breathing coating or surfacing system without some form of moisture mitigation. This test really only determines moisture at the surface of the slab.
Another popular test is ASTM F 2170 Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes. This test measures the moisture within the slab. Again, the industry has accepted a max of 75% relative humidity before moisture mitigation is required. It should be noted that both of these tests only measure the moisture condition of the slab at the time of testing. In fact, the most thorough experts recommend running both tests to get as complete a picture as possible.
It also should be noted that there is no correlation between ASTM F 1869 or F 2170 and ASTM E 96. Until recently, many 100% solids polymer-based materials have successfully been used as moisture mitigation systems. The only way to reproducibly test and rate these materials is with ASTM E 96 Water method. Virtually all of these materials were reported to have perm ratings between 0.1 and 1.0 perms. For example, APF’s VaporSolve™ systems have mitigated more than 20 million square feet of high moisture content concrete while displaying a perm rating of 0.60 perms.
It’s important to note that in 2013, ASTM issued a new standard ASTM F 3010 Two-Component Resin Based Membrane-Forming Moisture Mitigation Systems for use under Resilient Floor Coverings. This standard chose an arbitrary value of ≤ 0.1 perm. It is unclear how this value came to be, as so many high moisture content floors have been successfully mitigated using materials with perm ratings higher than 0.1.
Regardless of the reason, if a specification calls out this new ASTM F 3010 Standard, APF has developed VaporSolve LP (low perm) that has a perm rating of just 0.0333 perms.
As of this article, there isn’t any ASTM standard for membrane forming moisture mitigation systems for use under resinous flooring systems, and as such, APF has no intention of changing our standard VaporSolve system for use under APF resinous floor systems.
At the end of the day, if a “Class” is being called out, there is great likelihood that it’s mistakenly using building envelope vapor retarder specs. If you see a value stated in lbs/1000 ft/24 hr, it’s the tell-tale sign that they’re results from ASTM F 1869. And, if you see values stated in % relative humidity, they’re from ASTM F 2170. The only values reported from E 96 testing are perms (grains/h/ft2/in. Hg).
As a contractor or installation professional, the next time you take a look at those numbers, do so with a grain of salt and remember that all testing isn’t the same.