RH Testing of Concrete Floors - The Harsh Truth

RH Probes - What were these evaluated for? 

Although most of the earlier exaggerated claims have been removed, false claims still exist with what the RH measurements actually measure and how the data is consistently misinterpreted and misrepresented. I will cite directly from the sources.

The Lund University/Hedenblad Study (1997)

Although now obscured (which I believe to be intentional due to the consistent pattern of bold claims then withdrawal then denial of the bold claims), the Lund University Study was the impetus in developing the ASTM F2170 method.

What Was the Purpose of the Lund/Hedenblad Study?

Irrespective of claims to the contrary, the study focused solely on the initial drying rate of concrete after placement. Here are excerpts taken directly from the study:

The title of the Study - "Drying of Construction Water in Concrete" "The publication discusses the length of time needed by concrete structures to dry out after construction in order that damage to adjoining constructions and finishes may be prevented." 

Why the Study results (and subsequent studies and tests) are NOT applicable for concrete that has been in service - The drying times given cannot be used in drying out concrete after water damage. The reason for this is that old and mature concrete has different drying properties from those of younger concrete. The drying times given in this publication are typical values. Obviously, they are no substitute for moisture measurements but must be seen as a complement to these."

NOTE: Right in the very first page after the title/description the study clearly states this procedure is OBVIOUSLY "no substitute for moisture measurements." 

How clear and obvious does a study language have to be to prevent misapplication and misinterpretation of intent and evaluation?

Study acknowledges high alkalinity but does NOT differentiate high pH from high alkalinity, so the message gets muddled. 

"Damp concrete has very high alkali content. pH is never lower than 12.5 and may often be as high as 14. Cement of high alkali content produces a higher pH value in the concrete and thus entails a greater risk of degradation in e.g. adhesive and floor coverings." 

The above statement from the study clearly refers to "new" concrete since older and mature concrete can have a pH lower than 12.5. High alkali content can also be lower in pH, depending upon the type of alkaline, particularly after carbonation. 

Reaffirmation this Study was restricted to the mix water of concrete (NOTE: I added bold to "quantity of construction water which must dry")

"In making conventional concrete, often ca 180 litres of water is used per m' of concrete. Some of this water is chemically bound to the cement. Another portion is bound in the pore system of the concrete. The lower the water-cement ratio, the more moisture is bound chemically and physically, i.e. the smaller the quantity of construction water which must dry." Page 10. 

The deadly word "assume" creeps in, where an assumption is made without verification and again indicates a misunderstanding of the difference between high pH and high alkalinity! I have highlighted assume

"This means, for instance, that the diagrams for drying to 90 %rh applies for drying to RH = 87.5 % in a concrete with Slite cement and w/c ratio of 0.37. It is thus assumed that water of higher alkali content in a concrete with w/c ratio = 0.37 has the same effect on the flooring material at RH = 87.5 % as a water of lower alkali content in a concrete with w/c ratio= 0.7 at 90 %rh. The effect of alkali in lowering RH is demonstrated. In the adjustment of RH in the above table it is assumed that it is the quantity of moisture in the liquid phase which is in contact with the floor covering that determines the critical moisture state." Page 15

This above section is wholly incorrect in its assumption since alkalinity and pH are used as interchangeable terms, yet represent completely different conditions. High pH WILL reduce measurable RH, but lost in this study is that increasing alkalinity will CONTINUE to reduce the measurable RH!. 

The justification of results is based on a careful control of the ambient conditions, again based on freshly placed concrete, NOT concrete that has been in service! 

"Case f: Continuous rain for 2 months. During the first two months after casting it rains. Drying then takes place at + 18°C and 60 %rh. 14 28 days Time 2 months. 

Case g: Rain again after some drying. Normal conditions (Case a) during the first 2 months, followed by rain for 2 weeks. Drying then takes place at +18 °C and 60 %rh." Page 17" 

"There is an American standard (ASTM E 104-85) for RH calibration which specifies the salts to be used, the required purity of the salt and water, the requirement regarding temperature stability, etc." Page 24

Calibration of RH sensors (ASTM E 104-5) Commercial calibration kits based on ASTM E104 commonly include LiCl (≈11% RH) and NaCl (≈75% RH). 

WHY pointing out the calibration salts is important: The calibration salts, even though are mostly water are classified as "salt saturated solutions" where the salts used for calibration can no longer be dissolved into the water, hence achieving "saturation". The RH of these calibration salts is 11% and 75% respectively...it matters not if there is an ounce or a 100 gallons of a saturated salt solution, the RH is constant. Alkaline salts can vary in concentration and therefore vary in RH measurable by a RH Probe.

Different Errors

The Lund study points out critical errors that can be experienced, even when calibrating or recalibrating a RH Sensor.

"Examples of systematic errors are 

a. Systematic error in the salt solution used for calibration.

b. Non-linearity of the RH instrument.

c. Temperature during measurement is different from that during calibration.

d. Drift in the RH meter, i.e. the reading for a certain RH changes in time.

e. Temperature difference between the RH sensor and the concrete.

f. Moisture is measured at a temperature different from that "in service" Page 16 

NOTE: The most impactful and nom-disclosed to most who require or use these RH Probes are c, d and f. 

c: I have yet to see ANYONE disclose if the temperatures during calibration and insertion into the concrete has been conducted. this alone can create a challenge since proper calibration without this data cannot prove the calibration was done correctly, undermining any and all results...has ANYONE been shown this data? 

d: Even in field studies, it was noted that the were errors in the RH measurements as the sensors would "pin" at a higher RH and not adjust when RH levels would reduce during the testing. This required removal of the sensor, drying and recalibration before reinsertion, with differences being noted after this procedure....has ANYONE been warned of this possibility? 

f: The gradient portion of the concrete, which averages a depth of 0.75-10 inches into the surface will actively change in both temperature and humidity in response to the ambient conditions. In depth, these changes are extremely slow and do not reflect surface absorption or desorption of moisture, where a concrete surface can be saturated or dried, even as the 1.5 inch depth remains constant. So moisture can readily penetrate a concrete surface as the depth section remains stable..what do YOU think will cause a flooring failure, a stable interior environment or a dynamic gradient where the concrete can be saturated and WILL begin to actively absorb moisture, possibly to critical levels if the temperature of the concrete is within 10oF of dew point.

The Influence of Alkali on RH in the Concrete

This is the title of appendix #4, page 49 of the Lund Study. It is acknowledged, but woefully understated just how dramatic alkalinity and the presence of other hygroscopic materials can have when measuring RH. 

The quantity of alkali (sodium hydroxide NaOH and potassium hydroxide KOH) in the cement influences the RH measured in the concrete. The alkali in the cement is to some extent dissolved by water when the concrete is mixed. The more cement there is in the concrete, the more alkaline (basic) the concrete will be. Different cements contain substantially different contents of alkalis.

If the quantity of moisture in kg/m' is the same for two types of concrete which are identical apart from the alkali content, the measured RH will be lower in the concrete with the higher alkali content. Concrete with a low water-binder ratio can contain appreciably more alkali than ordinary concrete. This means that concrete with a low water-binder ratio can, at the same RH as conventional concrete, contain more moisture. This moisture which has a high alkali content - the pH value may be over 14 - can for instance cause saponification of the plasticiser in vinyl floor coverings, with bad odour as a result. As pointed out above, alkalinity depends on cement type and different mineral additives such as silica fume or slag.

One probable consequence of the fact that the same moisture content in concrete can produce different values of RH with different degrees of alkalinity is that there are no generally valid critical relative humidities RHCR1T' HCRITmay vary depending on the type of concrete and its alkalinity. This has not been generally known before. 

NOTE: This fact ALONE is WHY neither F2170 nor F1869 can be considered "quantitative" and the F6 committee is in error for allowing such a title and even to the point to where neither can be even considered a qualification on a stand-alone basis. 

Quantitative is based on known factors, with the most likely unknown factor being location and quantity of alkaline salts within the concrete. Even with known factors, to quantify also requires no significant deviation within a given context. Without context, quantification isn't possible.

Alkalinity in Concrete Even Affects the drying rate of Concrete and Errant Conclusions

The Lund Study makes an egregious assumptive error in the following statement from Page 50: 

"For two types of concrete which are identical apart from the alkali content one consequence of different alkali content is different drying times to one given RH level (e.g. 85 %rh.). The concrete with the highest alkali content has shorter drying time to the level than the concrete with a lower alkali content. This is due to a larger quantity of construction water has to dry out from the concrete with the lower alkali content to reach the given RH." 

The author assumes that removal or lowering of RH equates to removal or lowering of moisture content in the presence of alkalinity. In my view, this is an unacceptable misunderstanding of what alkalinity does as it concentrates: 

As water is removed, alkalinity increases, along with a reciprocal decrease in measurable RH. 

An alkaline/water solution at 20% NaOH has a measurable RH of 78% and as it continues to concentrate, the RH continues to reduce to where a 30% NaOH concentration has a measurable RH of 63%. This DOES NOT mean the concrete is dry, yet that is the assumption suggested by the authors. 

Concrete with a higher alkalinity has a different "dry rate" than low alkaline concrete since its equilibrium moisture content is naturally greater. 

A key issue is that any changes in the concrete chemistry also affects the RH of the concrete, which successfully supports the hypothesis that the continued changes in concrete need to be re-evaluated and ALL associated ASTM and other standards need to be updated to reflect these changes, yet most standards are based on concrete no longer used. 

How can ANYONE require test methods for a material of any kind that is substantially different from what was previously evaluated? That is an indefensible, non-supportable position, particularly when it has damaged those who did not follow such inappropriate requirements. 

Other RH Evaluations that need to be Questioned

The only published documentation for RH Probes are based around new concrete, with at least one of the studies conducted by a group with a vested interest (patent older). 

To establish validity, methods and products need to be tested by accredited and disinterested third parties. 

Worse, much of the non-facts circulated critical of moisture meters such as Tramex are by those with a vested interest in the RH Probes and NONE of them have any data to back up such critiques.

We NEED to Move Back to Reality in Moisture Testing

One of the most damaging, most disparaging and LEAST accurate claims by the RH Promoters is that Tramex moisture meters aren't accurate. 

The reason behind this push to discredit Tramex is to guard the false assertion and insistence that all moisture testing MUST be in acclimated conditions...well guess what, that claim is pure BS and I used to buy into that until I realized just how dependent waterproofers, restoration contractors and roofing contractors were on Tramex. 

What each of these professions have in common when the Tramex meters are used is that NONE of these professions require acclimation for accurate moisture measurement testing and in nearly all these conditions. 

Profit is the motivation in blocking accurate testing...conflict creates opportunity and as Tramex continues to gain wide acceptance, the money train that runs on confusion and conflict will come to a dead stop. 

Dear flooring manufacturers and installers, what do you think will happen when your required moisture testing no longer requires acclimation and the inevitable battles and conflicts with the construction managers, owners and general contractors end? 

Likewise, if these same groups continue the path of inappropriate testing, requirements and easily provable methods where most moisture mitigation systems were unneeded, unnecessary and a burden on the flooring installer, project scheduling and damaged reputations and obligated penalties that should never have happened? 

The potential legal battles could be endless and create a crisis within the flooring and coating industries. 

Save your headaches and bottom line, make the change. 

I will challenge any and all that take exception to the content of this article. Moving to accuracy will be a lot less stressful and a LOT less expensive than an endless line-up of lawsuits and settlements. 

Remember the words of the RH promoters when they moved to successfully supplanted the CaCl test method; "If moisture testing was so accurate, why are we still having failures?"