Getting the Most From Your Meters
June 11, 2009
One cannot properly restore a water-damage loss without knowing the answers to some basic questions. What materials are wet? How wet are they? Are the wet materials getting dry? What is dry? It is obvious, then, that restorers should know how to get the most from their meters.
Before we begin, I wish to thank a panel of experts who contributed to this article: Scott Warrington; Paul Laurenzi; Micah Richardson; Jeremy Reets; Tom Rochenski; Ron Colling and Kevin Fisher. These are some of the fine people that use, sell, and manufacture the meters we’re discussing, and I very much appreciate their input.
The three basic tools used by a restorer to learn what is wet and what is dry are the invasive or pin-type meter, the non-invasive meter and the thermo-hygrometer. These may be separate instruments or exist as multiple functions in one unit.
Invasive and Non-Invasive MetersInvasive or pin-type meters operate by detecting changes in electrical conductivity. Pins or probes are inserted into the material being tested. The resistance of the material between the two pins is read and displayed by the meter. The resistance is affected by moisture content.
The non-invasive meter uses capacitance to detect moisture. The sensor, in contact with the material being tested, sends a radio frequency signal into the material. Depending on the material and the meter being used, the signal may measure from depths from ¼ inch to slightly over 1 inch.
An advantage of a non-invasive meter is that it does not damage the surface being tested and can be quickly moved from one point to another. This allows the restorer to quickly scan a large surface, such as a wall, for moisture.
Scott Warrington, technical support specialist for Bridgepoint Systems, notes that pin-less meters can be affected by surface moisture and will display an average moisture content from the surface to the depth the signal reaches. Pin-type meters can read from just the tip of the probe and thus show the precise moisture content at any given depth, including beyond the range of a meter using a radio signal.
Meters are available that are calibrated to provide accurate readings on a variety of surfaces including wood, concrete, dry wall and so forth. Micah Richardson of Billings, Mont.-based Express Distributing favors one meter that can actually be switched to read any of 69 different species of wood.
Qualitative Vs. Quantitative ScalesMeasurements for wood typically display a percentage of moisture content. Scales for other materials are usually relative and provide a qualitative reading. The scale may range from 1 to 100, or 1 to 300. A reading on the lower end of a relative scale is drier than a reading on the high end of the scale, but the numbers do not directly correspond to moisture content.
According to Paul Laurenzi, vice president of sales and marketing for Delmhorst Instrument Co., drywall is an excellent location for mold to flourish. Having a quantitative measurement of the moisture content allows the restorer to make better informed decisions regarding remediation, he said. At least one meter on the market provides a calibrated scale that shows a quantitative reading for drywall.
Material Temperature and Meter AccuracyAdvances in technology in the restoration industry means that the temperature of the materials professionals are checking can be significantly higher than common room temperatures. Dave Hanks – both my brother and a valuable source of information – said, “Most meters are calibrated at about 70
AccessoriesThe proper accessories can make your pin-type meter useful for many additional applications such as checking insulation behind dry wall, sub floors, behind baseboard and trim, in ceilings and even books and documents.
The Slide Hammer or Hammer Probe has pins that read only from the non-insulated tips. This allows the restorer to get readings at various depths as you penetrate through floorings, walls or concrete. “Using a hammer probe from the under side of a wood floor to avoid repairs that may or may not be acceptable to the client. Think about having someone pounding holes into your wood floor,” Ron Colling, national director of restoration sales for Interlink Supply, said.
The Deep Wall Probe has 4-inch long insulated pins similar to the hammer probe. It is an excellent tool for checking stucco clad structures.
A Blade Electrode features two 5-inch-long blades bent at an angle and coated with Teflon so the reading is made only at the tips. This is useful when looking for moisture behind trim or base molding. It is also a great tool to check for moisture in books and documents.
An accessory called a Hygrostick is available for certain meters that enables one to check the relative humidity in a concrete slab. This information is extremely important to floor covering inspectors or those involved with installing floor coverings over concrete. Moisture emissions from concrete are a common reason for installations to fail. Being able to explain or prevent these failures is very helpful.
Thermo-hygrometersThermo-hygrometers detect and recording temperature and relative humidity. These numbers are used to determine if proper drying conditions exist and to chart the progress of the drying job. These numbers can be used to calculate GPP (grains per pound), dew point and vapor pressure. Interlink’s Colling notes that, “This can be done with a separate chart or calculator, but the restorer can save much computation time by using a meter that displays those readings directly. This can also eliminate errors in calculations.”
Of course accuracy is important, but there is another consideration to take into account when selecting a thermo-hygrometer. Water-damage technicians often make dozens of readings per day. The time required for the instrument to display an accurate reading, the response time or settling rate, may be a little as several seconds or a long as a few minutes. Considering the labor value of this time multiplied by the number of readings per day, week and month makes it obvious that spending a bit extra for the right tools pays off quickly.
And finally, some very good practical advice. Kevin Fisher, education program manager of Dri-Eaz Products says that, “If you want more accurate meter readings, meters that stay in calibration longer, and meters that last longer, always store meters in a case. Meters are scientific instruments that can be damaged by rough handling and extreme temperatures. Do not leave meters laying in your truck and expect good results.”