Moisture detector meters: tools for all occasions.

Last winter, a significant part of our institutional practice consisted of assessing indoor air quality in several schools, correctional facilities, and commercial establishments. We did not, however, conduct extensive air samplings; we passed that phase of the evaluation on to the trained industrial hygienists - and then only when absolutely necessary. As sanitarians, we set about following clues we received from the complainants and tried to identify as many conditions as possible that could contribute to contaminants in the immediate physical environment. To simplify this process, we relied on a moisture meter to identify the ideal conditions for mold fungi, the growth of other bothersome microbial contaminants, and harborage of insect pests. Through experience and through considerable review of the literature, we have learned that damp conditions, particularly those not readily apparent to the naked eye, abet some of the thorniest biological monsters out there.

Basically, all moisture detection instruments work about the same. They transmit AC signals from two electrodes into the material being tested. At any instant during the cycle, one electrode is positive and the other negative. When no moisture is encountered, the resistance is high and the signals are insulated from each other. When a material contains moisture, however, the conductivity increases by at least six orders of magnitude. This conductivity is reflected on the analog dial of the instrument. The readings are given as percentage moisture, which is ideal for wood and timber, and range from 10 percent to 20 percent, with 11 percent to 18 percent as the most clearly defined. Most moisture meters also have a relative scale that runs either 0 to 100 or 1 to 10. This scale is handy for defining wet and dry areas. We have found that we most often use the relative scale as a subjective indicator of moisture.

For almost three years, we have had numerous occasions to work with two relatively inexpensive moisture meters, each with its own unique features. These units complement one another, and we take them both on most indoor air quality investigations. The first, and more expensive of the two, is the Tramex Moisture Encounter manufactured by David White Tramex. This noninvasive unit features two soft scratchproof rubber pads (one positive and one negative), which measure relative electrical resistance. The unit can detect moisture on virtually any flat and relatively smooth surface. It has three scales: the first for wood and timber, the second for drywall and roofing, and the third for plaster and brick. Operation is simple, and the analog scale is easy to read. Select the relevant scale and switch on the unit. A flashing LED serves both as an indicator that the unit is on and as a check for its 9-volt battery. To operate the unit, place the rubber pads directly on the material being tested. Ensure that the pads are in firm contact with the surface. Then read the moisture directly from the scale. We particularly enjoy working with this unit when evaluating moisture in large areas such as walls, floors, and ceilings. For survey work, the nicest feature is an audible alarm that the unit emits at about the middle o[the percentage and relative scales. The Tramex Moisture Encounter costs about $320. It comes with a one-year guarantee and a carrying case.

The other unit we find quite useful is a compact pocket moisture meter: the Rapitest, which is manufactured by Sonin, Inc. Costing about $75, the Rapitest features a two-pronged sensor head at the end of a three-foot coiled cord that attaches to the meter. This unit, too, will measure moisture in wood, plaster, and brickwork, but the prongs make it ideal for gauging moisture in sheetrock, carpeting, fabrics, and other soft and fuzzy stuff. In fact, this little unit is a superb asset in food service inspections. We've used it to find moisture in warehouse commodities, composite and metal-clad wooden counters, other structural materials, and refrigerator insulation. It is also an excellent teaching tool: In conjunction with a stem thermometer, it can be used to graphically show bacterial growth conditions on a nasty wipe rag that hasn't been kept in a sanitizing solution. (Here you have to use what you learned in microbial ecology and your imagination.) In addition, if you're buying a house, boat, or old Ford Woody, this little gadget is invaluable. The unit fits nicely into a compact camera carrying case: The $8 case that is designed for the unit and is ordered separately isn't worth it. We have learned to protect the prongs with the cork from a champagne bottle (or any bottle of fine wine) when the unit is not in use.

As an aside, these units are also quite useful for locating and tracing roof leaks and water seepage, as well as assessing the extent of wet rot, hidden condensation, and fire damage. Additional uses include checking surfaces before painting, applying wallpaper, or laying floors or tile.

Powitz and Balsamo give these versatile units "two thumbs up." Both moisture meters are available through catalogues such as Professional Equipment, which you can reach at [phone] or <http://www.professionalequipment.com>. Or you can contact the manufacturers listed below:

* David White Tramex, P.O. Box 1007, Germantown, WI 53022; [phone].

* Sonin, Inc., 670 White Plains Road, Scarsdale, NY 10583; [phone].