It is Time for the Flooring Industry to turn away from using RH Probes

As third party studies come in globally, it obvious that not only are the current crop of RH probes used to measure RH in concrete flawed with an admitted effective range limited to between 10-90%, but the devices within this range have proven to be non-correlative with the relative success or failure of a coating or any other flooring material for that matter.

Worse, the emphasis towards using RH probes as an indicator of concrete moisture content is based on a series of false precepts:

1. RH probes are the most accurate method of measuring total moisture content. Comment: Right out of the gate, I contested this assumption that way too many concluded as factual. Water vapor within concrete is a minuscule amount of moisture when compared to capillary moisture. The percentage of moisture in vapor form, which is the ONLY form of moisture a humidity device can measure makes up less than 2% of the total moisture content of concrete less than 5 years emplaced.
2. RH Probes measure the moisture that will eventually migrate towards the concrete surface and is a "predictor" of future issues. This nonsensical sales-pitch has NO basis in fact. Unless in a desert region, or a climate where the underside of the concrete is consistently warmer than the interior, this claim violates the second law of thermodynamics; which dictates that moisture moves from warm to cool, higher pressure to lower pressure.
3. Water Vapor can brings alkaline salts to the surface (yes, that was actually claimed by one of the principles who market humidity probes - I was Gobsmacked). Comment: The hydrological cycle and the principles of distillation prove just the OPPOSITE of what this "expert" claimed. If you want to clarify liquid water, an effective method is to evaporate the liquid, which is now in a gaseous state and can no longer transport solids. Cooling this gas produces a nearly pure water. When it rains, the water will readily contact and absorb particles in the air, giving us that clean "after rain" smell since the water NOW can carry solids, effectively cleaning the air of contaminants. NOTE: Make NO mistake, it takes LIQUID water to transport solids, water vapor/gas/humidity will not and CANNOT transport solids. You can't even conduct a pH test without using liquid water, why?, because the alkaline salts and other soluble components register a pH ONLY in solution.
4. Warmer temperatures can increase the RH. Comment: When I first read that claim, I could scarcely believe what I was reading and wondered where such an easy to discredit idea could have originated...as I did more research, I was horrified to discover it was a prominent and very well-respected University that made such a claim. I have the study where this head-scratching claim likely originated since it is the same university that established the use of RH probes as a useful tool to measure the drying rate of the concrete mix water. This claim and others I have read in numerous studies have convinced me that those conducting these studies, have no clue as to the complexities the alkaline components of concrete can contribute to what prompted their head-scratching speculation of humidity increasing (even though there were no measurements that corroborated this assumption. I could write an entire article on the mistakes made in that single study, but for brevity's sake, it is too long and complex to try and explain here.
5. Humidity Probe Manufacturers have allowed measurements exceeding 90% to stand as unchallenged humidity percentages. Comment: Even in the initial announcement in articles such as one that appeared in a CFI publication, the effective range specifically stated was 10-90%. Comment: In every third party study I have read, both under laboratory conditions and field conditions, it has been noted that ANY measurement exceeding 90% was unreliable! Further, sometimes the sensors would get "stuck" where the actual humidity levels would be reduced, but not reflected with the probe. These researchers ALL stated this required the removal of the sensor, drying the sensor and recalibrating before reinserting before the "stuck" sensors would recognize the lowering of the humidity.
6. Humidity Sensors, even with the same manufacturer, differed under controlled testing. Comment: One laboratory in particular studied 4 different humidity sensors used for concrete probes. Two of the sensors were from the same manufacturer. Each sensor, evaluated using standardized calcibration solutions found that NONE of the sensors actually reached the anticipated target. One was consistently high (and happens to be one of the most used sensors in the flooring market) and another was consistently low as compared to the baseline calibration solution. This was consistent with all three calibration solutions.
7. Humidity Sensors are appropriate to determine the suitability of a flooring installation. Comment: first off, NONE of the humidity probe tests were determined suitable for an existing concrete surface. The studies have been confined ONLY to the initial drying rate, with caveats within the appendix of the study cautioning that alkaline concrete and concrete that has been inservice or even rewetted will have different results....that little detail somehow got lost in the sale-pitch.
8. ASTM F 2170 is THE Standard for determining "dryness" of concrete. Comment: First off...READ THE STANDARD! It says in NO uncertain terms that this measures the relative humidity in concrete. The standard does NOT say or claim anywhere in the standard that it measures the moisture content of concrete. What is Relative humidity? It is water, in its gaseous form that exists in an air space. F 2170 measures where the concrete ISN'T - NOT the concrete itself. Anyone who says differently is either misinformed or is intentionally lying, there is no other way to put it.

Conclusion

RH probes are a useful tool, when used correctly. Unfortunately, the entire concrete and flooring industry had been misled into believing otherwise.

This needs a reset and I cannot emphasize strongly enough to STOP using RH Probes until you understand exactly what it is these measure and what the measurements mean and how to interpret the data. I will give an example:

ALL salts WILL reduce measurable humidity...read that again....

ALL concrete contains salts, we just don't know how much or where these salts may reside.

What we DO know is that these salts tend to collect in the surface of the concrete. I have had some debates and discussions on this, so let's put this to rest once and for all:

Years ago, I theorized that concrete surfaces could suffer a form of ASR (Alkali-Silica Reaction), causing disruption and damage to virtually any type of flooring material or coating. I was ridiculed right from the start with some of these experts telling me that ASR was time-dependent and early ASR wasn't possible.

Well, a couple years after going public with my theory, studies began to come out, verifying my theory WAS correct and this DID happen, and not only did it happen, it may be fairly common. This early ASR was given a term called NSASR (Near Surface Alkali Silica reaction).

What causes ASR is when a strong and concentrated alkaline salt quite literally dissolves certain types of aggregate, forming a sodium and/or potassium silicate that is in a dynamic form (usually referred to as a "continuously imbibing gel").

The recent debates where my theory cited surface alkalinity was the main culprit in creating a self-desiccating surface within the top one inch of the concrete was questioned, I would ask them if they knew about the NSASR. Most, if not all answered they knew about it and agreed it was now well-established, I would counter by stating, this indicates the surface IS alkaline, and it would take MUCH less alkalinity to self desiccate a concrete surface than it would take to initiate NSASR. (crickets).

I then outlined that ALL salts will reduce humidity to greater and lesser extents, and two of the most dramatic examples exist in ALL freshly placed concrete: calcium hydroxide and sodium hydroxide.

When the initial cement reaction takes place, this lowers the water volume available for additional cement formation. This in turn, increases the alkalinity (concentration) of the alkaline salts.

As sodium hydroxide becomes increasingly concentrated, it reduces the solubility of calcium hydroxide which in turn can reduce contactable non hydrated clinker (non-reacted cement) surface.

The increase in alkalinity has a reciprocal reduction in measurable humidity: a 20% water/sodium hydroxide solution will produce a humidity of 78%. This is now too dry for cement formation to take place. At a 30% concentration, the measurable RH would be down to 63%. Cement will NOT form if the RH is lower than 80%.

It is ironic that the targeted "dryness" for a "safe" flooring installation according to many flooring manufacturers, may instead be delivering a very alkaline concrete that is full of water and one of the worst-case scenarios for any flooring type.

RH Measurements without context is an inexcusable disservice to the flooring industry and a large part of why moisture-related claims have tripled in recent years.

I will once again cite one of the prominent humidity proponents as they moved to displace CaCl (ASTM F 1869) as the preferred method of testing with the statement; "If moisture testing is so accurate, why are we still having failures?"

I ask THEM: "If RH Probe testing is so accurate, why have problems become even worse?".