The flooring industry has collaborated to create a universal “one value fits all” criterion for the acceptability of a concrete slab to receive installation of resilient flooring materials (using adhesive). This single value is based on the results of a Moisture Vapor Emissions Rate (MVER) test performed on the slab surface in accordance with ASTM F 1869, “Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.”
The literature from many flooring installers and manufacturers states that installation of glued-on flooring cannot begin, and warranties on flooring materials will not be honored, if MVER results are greater than 3.0 pounds/1000 square feet/24 hours (abbreviated in this article as simply 3 pounds); some manufacturers today have increased that to 5 pounds. It is not clear if this value refers to the results of any single test, of all tests, or the average of all tests required by ASTM F 1869 to be performed on the slab simultaneously. That 3-pound upper limit of acceptability is also memorialized in ASTM F 710-11, “Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring,” Section 5.2, Table 1.
On several logical, engineering, and scientific levels, it can be shown that the 3-pound recommendation is severely flawed, invalid, and meaningless as a relevant criterion for the installation of flooring materials on concrete slabs. No data of any type, numerical or otherwise, has ever been produced by the flooring industry, or any other source, to validate the 3-pound criterion. Some argue that the 3-pound criterion was arbitrarily established by the flooring industry at an unrealistically low level in order to invalidate warranties on flooring material, effectively an industry license to blame flooring failures on something other than the flooring itself.
Robert Higgins, a flooring consultant based in San Diego, and an eloquent representative of the flooring industry, wrote in Concrete Construction in 2004:
“Most concrete slabs in California (estimates are that 80 percent to 90percent of concrete slabs are between 11/2 and three times the maximum allowable level of 3.0 lb) are well above the maximum allowable moisture level for ‘safe installation’ of a given floor, yet less than one out of 10 experience problems or failures that can be attributed to moisture alone. This statistic alone invalidates moisture as the root cause of failure.”
We fully agree with Higgins’ discussion and conclusions. We have reviewed thousands of MVER test results performed on mature residential concrete slabs (those in which excess construction mixing water has substantially evaporated) and found that the vast majority of those results are between 4.5 and 9 pounds as Higgins states. Only rarely is a result below 3 pounds reported. We also agree that there is no relationship between flooring failures and the results of moisture dome tests. We have seen similar flooring distress on slabs with very low MVER results and others with very high MVER results. The use of 3 pounds as a borderline establishing the acceptability of glued-on flooring is invalid on the basis of history and experience alone. It simply cannot be used as a predictor of future flooring success or failure, nor as a verifying factor of flooring failure if it occurs.
Conditions affecting results
Several technical reasons explain why the 3-pound criterion is invalid. The MVER test is significantly affected by environmental conditions existing at the time of the test, both above and below the slab. It is also heavily affected by slab surface preparation techniques.
The importance of above-slab conditions is nominally acknowledged by ASTM F 1869 in Section 6.1. It requires the test be run within an air temperature range of 65 degres F to 85 degrees F and relative humidity (RH) range of 40% to 60%. Studies we have done show that the results of MVER tests run under otherwise identical conditions will vary by plus or minus 30% within those ranges. The results appear to be proportional to both temperature and RH. Test results increase with an increase in either parameter. They likewise decrease when either parameter decreases.
This means that a moisture dome test result of 2.9 pounds run with an above-slab temperature of 65 dregrees F and RH of 40%, and then run again in the exact same location with a temperature of 85 degrees F and RH of 60%, all other conditions equal, would yield a result of 3.8 pounds, with both tests being fully within the ASTM methodology. According to the flooring industry, one test would conclude that installation of flooring is acceptable; the other that it was unacceptable. These directly conflicting conclusions would be a sole function of above-slab environmental conditions that have nothing to do with any known or measurable property of the concrete slab or the ability to install flooring. A simple change of the weather would lead to apparent slab unacceptability to receive flooring.
Below-slab conditions have an even greater influence on MVER results, yet these are completely ignored by the flooring industry. A study we did some years ago reported that a definitive relationship exists between the results of MVER tests and the temperature of the slab-soil interface at the bottom of the concrete slab. Other environmental conditions being equal, as the below-slab temperature increases, so do the results of the moisture dome test. Thus MVER tests performed on the same slab, in the identical location, with identical above-slab environmental conditions, using test kits from the same manufacturer will be significantly higher if they are run in the warmer summer months than if they are run in the cooler, winter ones. This is shown in the graph on page 36.
The relationship shown in the graph was established by performing, over 16 months (October 1998 through February 2000), a series of 54 MVER tests in the same location with similar above-slab conditions on a concrete slab, measuring and recording the below-slab soil temperature during each test. The relationship between below-slab temperature and MVER is approximately linear. As can be seen, the range of temperatures measured under the slab in this 16-month test period was between 60 degrees F and 72 degrees F, and the test results at the same test location varied between about 4.0 and 10.4 pounds. Thus a 12 degree F decrease in temperature below the slab resulted in roughly a 6.4-pound decrease in MVER, or a gradient of 0.53 pounds/per degree of below-slab temperature change.
It is our opinion that the gradient, or relationship between temperature and MVER results, is reasonably applicable to all tests run with similar above-slab conditions and with kits from the same manufacturer. Thus every 10 degree F increase in below-slab temperature results in an increase in dome test result of about 5 pounds, all other conditions being equal. Our experience is that low MVER results are virtually never reported in summer months when below-slab temperatures are at or above 72 degrees F.
Conclusions
We have shown that MVER tests run at the identical location can indicate that the slab is either acceptable or unacceptable for flooring installations, depending on environmental conditions alone, independent of any slab or concrete property. Further, just the normal variation inherent in moisture dome testing, regardless of environmental conditions, can commonly produce test results run at the same time that are both above and below the 3-pound limit on acceptability, which itself has never been proven to relate to anything.
Thus, based on historical experience, the large inherent variability in the test itself, and the variability in test results as a function of ambient environmental conditions, the use of a falsely low and static criterion of 3 pounds is completely invalid and basically meaningless, except to imply falsely that the concrete slab is somehow unsuitable to receive flooring. There should be no limit enforced because the test itself is fundamentally flawed. But, if some limit was to be applied rigidly, it should be applied at a single, very narrow temperature range.
Alternately, if legitimate criteria for acceptability of slabs by MVER values were to be set, they should take into account the ambient concrete and soil temperatures and the relative humidity, making the limit dependent upon the actual conditions, not the assumed ones.
The 3-pound limit and the MVER methodology are contrary to good science: They cannot and should not used to characterize any mature slab for any purpose.
— Ken Bondy is a consulting structural engineer in West Hills, Calif., and Geoffrey Hichborn Sr. is chief engineer - lead consultant, for Building Forensics International, Anaheim, Calif.
