Electronic moisture meters are rapidly becoming an important, even essential, item in the contractor’s toolbox.
At one point not too long ago, these tools were rarely — if ever — seen in the possession of a dealer/contactor. One might’ve seen a moisture meter in the hands of an inspector who was utilizing the instrument in the course of determining the cause of a flooring failure. Even then, not every inspector would use the tool, as the values they expressed did not have meaningful significance to the flooring industry at large.
At the time, electronic meters were not utilized to any great extent mainly because they measured moisture content — not a vapor emission rate, as the calcium chloride dome test does. As specified in ASTM F1869-98, the moisture dome test determines the moisture vapor emission rate of concrete by gauging the weight change in a sample of calcium chloride that’s placed in close proximity to the slab for a predetermined amount of time.
Many flooring manufacturers could not equate the meter’s moisture content values with those of the calcium chloride test, which has long been an accepted method for evaluating the condition of a concrete slab. In fact, I don’t know if it can ever be shown that there is a correlation between a moisture content test result and a dome test reading expressed in pounds-per-day emissions. The problem of correlation, as I see it, is that the electronic moisture meter reading is a static value, whereas the moisture dome test yields a dynamic value. In other words, the value expressed by the electronic meter represents moisture “at rest,” while dome test results are an expression of moisture “in movement.”
The availability of electronic moisture meters has greatly improved. Today, both floor covering distributors and wood flooring distributors now carry meters in their product groups.
Some electronic meters measure the moisture content via an electrical resistance test. First, a pin-type meter is inserted in the concrete by drilling holes or driving two concrete nails into the concrete. These holes are used as the contact point for the two pins of the instrument. The procedure is a conductivity test; the more moisture, the better the conductivity, which results in higher readings.
Other meters are of the impedance type. This meter measures the electrical AC impedance. Impedance (for us dummies) is an alternating current measurement that combines resistance and impedance. The depth of the wave signal penetration will vary depending on the slab and moisture content. Depth generally varies from ¾ inch to 2 inches.
There will be a new kid on the electronic meter block within the next year or two. ASTM is developing a standard for determining the relative humidity of a concrete slab. For many years, the Carpet and Rug Institute (CRI) has relied on a relative humidity evaluation.
A number of fine testing units are available. I will name some with which I have first-hand experience and apologize, in advance, for those I neglect to mention. I prefer to discuss the just the units I’ve personally used or seen used.
The Delmhorst BD-2100 is a pin-type meter that I’ve used successfully for concrete and wood moisture evaluations. I have also used this type of meter for evaluation of gypsum poured underlayment, because the calcium chloride dome test produces inaccurate results when used over gypsum.
Another electronic meter in wide use is the Tramex Concrete Encounter. This is not a pin type. Rather, it operates on the wave signal system. This unit is popular with the wood flooring industry.
Other well-known names, especially in the wood industry, are Lignomat, Wagner and Protimeter. Lignomat’s DX/CW/E-16 is that company’s most versatile, in my opinion, because it measures most everything. Lignomat’s S/CW/E-16 measures moisture in concrete and other building materials. Wagner’s Concrete C575 is a wavelength type of meter with an analog, rather than digital, display.
Based in England, Protimeter manufactures a variety of instruments. Protimeter’s MMS, an instrument that measures relative humidity, will apply to the future ASTM standard.
In addition, many companies in the flooring industry use products made by Surveymaster. Another popular device is NDT James Instrument’s Aquameter.
Granted, this list is by no means all encompassing. However, I hope I’ve given you a feel for some of the well-regarded moisture meters. To obtain additional information, I urge you to contact the companies in the list that accompanies this article.
**Information about products mentioned in this column can be obtained by telephoning the following.
Dellmhorst: (800) 222-0638
Lignomat: (800) 227-2105
NDT James: (800) 426-6500
Protimeter: (800) 321-4878
Tramex: (303) 972-7926
Wagner: (800) 858-7609