Electric Moisture Meters - 11/15/2004 - Home Interior Attic Basement

Electric Moisture Meters

A cost-effective tool that can easily determine moisture levels.

How wet is too wet? Some moisture is unavoidable and may even be necessary in building products, but too much of it causes mold, decay and other performance problems. Previously, determining moisture levels in these products has been a time-consuming and somewhat destructive process. A solution is the electric moisture meter-a cost-effective tool that can easily determine moisture levels and diagnose resulting problems.

Moisture meters are designed to measure the moisture content of various building materials such as wood, gypsum board, plaster, concrete, brick, roofing and insulation. Moisture meters are used for quality control to ensure proper moisture levels of building components prior to installation. They also are utilized to detect problems after construction.

Electric moisture meters use known relationships between electrical properties and moisture levels in materials that are hygroscopic (able to absorb water from the environment). The moisture meters come in two varieties: conductance and dielectric.

Conductance meters have two to four metal probes, or pins, that are physically inserted into the building material. They read the moisture content of the material through the electrical conductance detected between electrodes. Higher moisture levels facilitate better electrical conductance, thus higher moisture readings. Moisture level displays for these conductance meters include analog (needle indicator) and digital (alphanumeric indicator) displays. Digital displays utilize liquid crystal (LCD) or light-emitting diode (LED) technology. Since wood species affect the readings, these meters are commonly calibrated to default settings for Douglas Fir.

Dielectric-type moisture meters are noninvasive-they do not physically puncture the material. They generate an electrical field through flat platens located on the bottom of the meter. These, in turn, analyze characteristics about the electric field to generate a moisture content reading. Moisture display options for this meter type are identical to the conductance-type meters: analog and digital.

Although the relationship between wood moisture content and electrical properties is well known, it is only predictable for a range of moisture values. Conductance-type meters are accurate for a wood moisture range of 7 to 30 percent moisture content and dielectric meters are accurate from 0 to 30 percent moisture levels. Moisture content readings above 30 percent provide qualitative information and do not necessarily correspond to the actual moisture content.

Moisture meter readings for materials other than wood also are useful in a qualitative capacity and should not be interpreted as actual moisture levels unless verified by a moisture detection method other than meter.

Other limiting factors associated with moisture meters include temperature, moisture distribution, material species or density, material thickness, and material coatings or treatments. Meter readings must typically be adjusted if the readings are taken at a temperature other than the meter calibration temperature. These adjustments are either performed by the meter if the temperature at the time of moisture reading is entered into the meter, or adjusted by the operator using charts to obtain actual moisture content levels.

Conductance meters are particularly sensitive to temperature and wood species. Readings must be corrected for species other than Douglas fir. The length of the electrodes (pins) and the ability of the operator to effectively drive them into the measured material limit depth of moisture detection. Effective depth of moisture detection for dielectric meters is up to 2 ½-inches (63.5 millimeters [mm]).

Dielectric meter readings are particularly influenced by material density and often require correction or calibration. Dew or surface moisture on building materials may give erroneously high readings.

Moisture meter prices range from slightly over $100 to $1,400 depending on quality, features, and accessories. A good quality meter can be found in the $250 to $400 range.

Not Applicable

Measuring moisture levels in wood using electrical moisture meters is an approved method when conducted in accordance with ASTM Standard D 2016. For materials other than wood, electrical meters provide only a relative scale of moisture content.

Not Applicable

Not Applicable

Not Applicable

The use of a moisture meter can offer cost-effective verification of the moisture content of building materials prior to installation. Improper moisture content often leads to customer service problems after installation in the form of mold, drywall cracks, nail pops, squeaky floors, unacceptable crack width in wood flooring, and paint failure. Moisture readings on building materials can be performed in mere seconds compared to hours or days for other methods. Unlike other methods of moisture determination where some of the tested material is rendered unusable during the testing process, dielectric moisture testing is non-destructive. Conductance meters will, however, leave two or four small punctures ("snake bites") where the electrodes penetrate the material during the test.

Some moisture meters have the ability to store data, perform statistical calculations, and download data to a computer, making them useful for quality control program analyses.

Moisture meter prices range from slightly over $100 to $1,400 depending on quality, features, and accessories. A good quality meter can be found in the $250 to $400 range.