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Guide to Understanding Moisture Meters and The Factors That Affect Wood Material Testing

The moisture meter is a common tool utilized by many professionals in the home inspection and construction industries. Designed to enable users to accurately reveal moisture content levels in a range of materials, moisture meters are generally easy to use and require only a general understanding of its function. However, without a proper understanding of the many specifics and features of each particular moisture meter, as well as a sufficient knowledge of how a variety of factors can also affect moisture level readings, it can be easy to use the tool improperly, thus resulting in a reading that is not entirely accurate.  

Moisture is a major concern to those in the construction and inspection industries, and proper usage is essential to ensuring that tests are conducted efficiently so as to provide the best possible results. There is a range of moisture meters available for testing a wide selection of different materials and substrates. Moisture will affect all materials differently, from concrete to sheetrock to dozens of types of wood materials.

Typically, for testing moisture content in wood, a pin type moisture meter will be used. The conductance meters use an invasive method of performing a test, by way of pin shaped electrodes of varying lengths. These pins usually range in size from 3/8-inch to 3 inches, and are inserted into a wood material. The pins then measure the conductive current that runs between the two electrodes and the resistance to the flow of the direct current through the material. This reading is converted to a moisture content result. A high conductance reading means that more moisture is present within the wood.

Pin type meters, also referred to as invasive moisture meters, are equipped either with insulated and non-insulated pins. The insulated pins are usually longer than non-insulated pins, and are coated with a non-conductive material except at the tip. The long pins are usually driven into the wood using a slide hammer device or similar tool, and take readings only at the conductive area of the pins. Non-insulated pins will take a moisture reading between the pins wherever the moisture presence is highest.

This can sometimes result in very different readings depending upon how far into the wood the pins are inserted and where along the length of the pins the reading occurs. For more accurate readings at precisely specific points and depths in the wood, insulated pins are a more ideal solution.

Conductance meters should also be adjusted for the different types of wood that may be encountered, and the area temperature can also be a factor that affects the readings. The manual that accompanies a moisture meter should provide instruction on how to adjust the meter for these specifics. Some engineered woods contain glue or resins that may also affect the readings.

Non-intrusive meters can also be used to measure moisture content in wood and materials. The difference between these meters and the pin-type meters is that it does not penetrate the material and does not utilize pins to take readings. Instead, the meter is placed against the material, and a plate with a specific range and depth of sensing ability takes an average reading of the entire area that can be read. This type of meter is also referred to as a capacitance meter. The capacitance moisture meter has the ability to take several readings in a short amount of time.

Many different factors must be taken into consideration when taking readings with either type of moisture meter. In addition to the specifics of each type of meter, the depth capacities of each meter must also be known, as each meter can be calibrated to different depths.

Additionally, the presence of surface moisture on a material can result in a widely skewed reading, and pins on pin-type meters should be kept in top condition. Replacement pins can be purchased for many meters to ensure accurate readings. When using pin-type meters, you should be aware that the pins obviously leave holes in the material. If this is a possible issue, a non-invasive moisture meter should be used.

Most invasive moisture meters are designed to be used parallel with the direction of the wood grain, but not all. The manufacturers guidelines should detail in which position the meter should be used for best results.

For non-invasive moisture meters, you should be aware of the size and depth of range that the meter is capable of reading, and the meter should always be in full contact with the material.

For construction and inspection trades, providing accurate readings and the accompanying documentation of the results can be a key component of a professional installation or inspection. Be sure to record all results precisely, to better ensure that the readings were taken correctly.