When to know a moisture test method is questionable - Part 1

When I first left my former company, I embarked on a quest of sorts to try and discover if there was a method of testing concrete moisture content that 1. Was accurate, 2. Made sense, 3. Wasn't prohibitively expensive, 4. Wasn't overly complicated and lastly; obtained results in a reasonable period of time.

Quantitative Vs. Qualitative

In most testing, unless it is a product where specific moisture content(s) can create spoilage issues, or a moisture content is critical, then quantitative measurements are important, if not vital.

Conversely, if thresholds exist for a given material or product, qualitative measurements are equally important, and simply knowing what the threshold is for a yes or no, or a go, no-go approach; quantitative measurements can be an expensive and unnecessarily redundant measurement. WAY too often, this distinction is either overlooked or not well understood by those being told to conduct moisture tests, and many times even by those requesting such tests.

Moisture Testing; When and Why

This next statement will hopefully initiate some dialogue; in the 40+ years I have been involved with waterproofing, restoration and rehabilitation of buildings and structures, the most error-prone industry for designating nonsensical "limits" and/or unrealistic moisture levels has been the flooring industry. This is a classic case of the blind-leading-the-blind.

My first experience with this occurred in the late 1980's; I had a conversation with a good friend and colleague (who has since passed away) Joe Grady, who COMPLETELY independent of me and we knew NOTHING of what the other was doing, compared the (current at the time 3.0 and 5.0 lb MAXIMUM moisture limits, via the calcium chloride tests) percentage of failures vs the currently used numbers. We were surprised and delighted that we were nearly identical in the assessment of flooring failures vs exceeded the "maximum limits".

At that time, more than 80% of the flooring installations were placed over concrete where the average moisture readings were ranging from 5-9 lbs. Here's where it get interesting; more than 90% of the floors placed over what should have excessive moisture, exceeding the maximum limits by sometimes more than 300% weren't failing. There was essentially NO correlation between the numbers obtained and the flooring problems. NOTE: In retrospect, whether or not the concrete was properly prepared was left un-noted, this supports the difficulties involved of knowing when a specific concrete surface HAS been properly prepared.

The second (and very profound) experience was with RH Probes where "maximum" limits were placed and there were projects where assigned responsibility for damages whenever a floor failed and the RH probe numbers were in excess of 90%.

I wanted to see if I could establish any baseline numbers where floors could successfully be installed versus humidity conditions where the floors would fail.

I wanted to start with successful installed floors and to my surprise and the surprise of others I have shared this information with; most floors I tested that had been successfully installed for weeks, months and even years, the RH rarely measured below 90%.

Since the "maximum" allowable humidity rates, much like the earlier "maximum" allowable moisture emission rates were NOT correlating with flooring failures; there HAD to be other factors involved.

Dew Point and Condensation

The ONLY time I found RH to be significant is when the humidity levels were within 10oF of dew point (5oC). This finding correlated with the LONG understood axiom of NOT painting a surface that was within 5oC of dew point (misinterpreted, which I confess to having done initially) that the 5 degree number referred to Fahrenheit. Instead it referred to Celsius.

As I began to use fans and sometimes dehumidification (particularly in non-conditioned spaces), once the RH levels were well away from the 10oF difference, the floors stopped failing due to "moisture". This is one of the issues that caused me to walk away from a "successful moisture mitigation" business...we were "repairing what didn't need to be repaired, it was a simple case of misdiagnosis, and slapping a low to non-permeable mitigation product was in the great majority of cases, a complete waste of time, money and resources. NOTE: When concrete absorbs moisture from the ambient conditions, subsequent moisture tests, with virtually no exceptions has ASSUMED the measured moisture originated FROM the concrete, NOT the ambient conditions. Moisture tests measure the presence of moisture, NOT the source.

The Quest For Moisture Test Accuracy

Shortly after I left my company, as I began to research moisture test methods and I placed my prior prejudices aside, I was surprised to find that most test methods are somewhat accurate to VERY accurate, FOR WHAT THESE WERE DESIGNED TO MEASURE!

What I found that shocked and horrified me was that most moisture tests are conducted without ANY context to what the moisture measurements mean, represent, or what could interfere with a "pure" result. Even the companies that sell these different methods for the most part do not understand concrete. How can you accurately "test" or instruct OTHERS to test something you don't understand?

All humidity measuring devices measure water vapor/humidity. These do not and CANNOT measure moisture once it is in liquid form or absorbed by a semi-permeable solid, such as concrete. Yet RH probes have been represented and sold as a method of measuring the moisture content of concrete.

I very publicly took issue with such claims and have watched the claims change from; Measures the total moisture content of concrete to - Measures concrete moisture to - Predicts future conditions to - Measures the moisture condition (whatever that is supposed to mean). With one of the bolder claims stating accuracy and scientific nature of the tests.

There is little to no value in either accuracy or scientific approach if they are aiming at the wrong target. 100% accuracy when hitting the wrong target is a 100% miss.

Humidity tests (and to a lesser degree) calcium chloride tests are affected by the presence of hygroscopic materials, particularly alkaline salts. In fact ALL salts will reduce the moisture measurements of ANY method that depends on an open system where there is no hinderance to evaporation, concrete is NOT one of these!!!!

Concrete contains a variety of hygroscopic materials that can vary from load to load, from top to bottom (lighter aggregate, which tends to be more hygroscopic, will be more concentrated towards the top surface of the concrete), and even within the same load depending on how the concrete is delivered and placed.

I will once again use the industry standard calibration solution as an example. The solution contains salt and water. The solution, irrespective of volume maintains a constant RH of 74-76%. As long as the salt is present in the water, the humidity CANNOT exceed 76% humidity unless the salt is diluted with more water; even then it would require the virtual absence of salt for the humidity to reach 100%.

Inherent Issues with RH Probes

To complicate matters even more, it has been discovered that currently used sensors are not precise and may contain significant flaws when humidity levels are between 90-100%.

In the studies where this was discovered, it was also found that these sensors can get "stuck" at an elevated level. So even if the humidity level decreases, these decreases may not be measurable by these sensors. It was discovered by these researchers that the only way to ensure the lowering of humidity was measurable was to remove the sensors, dry them completely and re-insert them.

I have yet to read ANY of these caveats from any of the current suppliers of RH probes.

Rhetorical question: What would happen if a flooring contractor or manufacturer got sued, then discovered later that the "excessive humidity readings" may have been due to this inherent flaw and that the liability they incurred was due to what is essentially a defective measurement? It is a virtual certainty that many have been held accountable for "damages" caused by "excessive humidity" but are unaware of this issue.

It would hit the fan, particularly since this flaw has been discovered and published into the public domain; and most importantly, I have yet to see ANY contradictory data or viable challenges contesting this discovery.