Water Moisture - Type of Moisture Meters
Moisture meter is an essential instrument used in many industries to detect moisture content in materials. Home and building inspectors rely on moisture meters to identify potential problems and damage to structures from moisture buildup. Woodworking industries, such as furniture makers, use wood moisture meters to insure a quality product. Flooring contractors use moisture meters to determine ideal conditions when installing a floor over a concrete slab or sub-floor.
Indicator scales on moisture meters can vary in appearance, but all will indicate moisture content in percent (%MC). While some moisture meters offer an analog scale, others read %MC digitally. The accuracy of the %MC readings, as well as the appropriate substrate scales, varies per meter and can vary by brand and type.
Most moisture meters are calibrated to wood, which provides a relatively accurate reading in wood moisture content. Typically, this scale ranges in the 5 to 40% range. When testing the moisture content in non-wood materials, such as concrete, a relative scale of 0 to 100 is often used, where 0 is bone dry and 100 is saturated. This is a relative scale. Moisture meters include visual LED indicators related to the percent reading on the scale for dry, moderate and saturated or wet readings. Additionally, some meters also offer a third scale for readings of gypsum. These scale readings can range from 0.2 to 50% moisture content. When selecting a moisture meter for sheet rock, it is advised that a moisture meter that offers a scale reading for gypsum be used.
Color indicators on moisture meters are helpful in determining whether the material being tested is considered dry or if there is a potential problem with moisture. The green (dry), yellow (moderate) and red (high) indicators typically identify where on the scale of %MC the readings occur. This can clear up confusion where one interprets a %MC as dry versus one that is moderate and may require more thorough investigation to determine if a problem with moisture in the material exists, especially if a visible sign of moisture does not exist.
Types of Moisture Meters
There are three common types of moisture meters used for the inspection of building and structure materials: pin-type, pin-less and pin/pin-less/all-in-one. All three types of moisture meters offer specialized purpose and are unique to the end user's application in determining %MC in materials.
Pin-Type Moisture Meter
The first of the three types of moisture meters is the pin type. Pin-type moisture meters measure %MC at the depth of the head of the contact pins. Pin-type moisture meters have two pins on the instrument, which are used to penetrate into the test surface at a desired depth. The reading of %MC is determined by measuring the electrical resistance between the tips of the two pins. This method of inserting pins into a surface is often viewed as an invasive process for measuring %MC. Typically these moisture meters will read up to 5/16" depth.
Pin-type moisture meters use the principle of electrical resistance to measure the moisture content in materials by measuring the conductivity between the pins. The tips of the pins are relatively sharp, uninsulated and penetrate into the surface for a sub-surface reading. With pin-type meters, you can also obtain a reading by touching the pins to the surface for testing. Most pin-type moisture meters use a scale calibrated to wood, however this does not mean that the meter cannot be used to measure moisture in other substrates and materials. This type of moisture meter can also be used for, but is not limited to, concrete, drywall, ceiling tiles and painted surfaces. When using the wood scale on a pin-type moisture meter, the %MC reading can range from 5% to 40% in moisture content. Generally, the low end of this reading falls into the 5 to 12% range, the moderate range will be 15 to 17%, and the high or saturated range will read above 17%. Scales for MC% ranges are provided in the instrument instructions and should be consulted concerning measuring ranges for particular surface materials.
Pin-type moisture meters are useful in measuring %MC in wood flooring, drywall, painted surfaces (such as the exterior of the home), carpeting, ceiling tile and cement. A pin-type moisture meter is the best way to identify the exact location of moisture buildup. A pin-type meter uses two pins that penetrate into the test surface at the user’s desired depth. When insulated contact pins are used, only the uncoated tips are exposed, providing an accurate reading of moisture content at various levels of penetration. Pin-type meters are the only instruments that allow the inspector to identify exact location of moisture at a given point. Using a pin-type meter is an effective way to determine the difference between shell and core moisture content. In some cases, the depth of the reading exceeds the length of the pin on the meter. If this is the case, many meters are equipped with a connection option to add accessory probes that can be inserted further into a substrate for more accurate core or depth detection. An example would be for Exterior Insulated Finish Systems (EIFS) testing.
Pin-less Moisture Meter
Pin-less or noninvasive moisture meters operate on the principle of electrical impedance.
This meter provides a nondestructive measurement of moisture in wood and other substrates, such as concrete and gypsum. A noninvasive moisture meter may also be called a nondestructive or a pin-less moisture meter. Scales on these meters are similar to that of pin-type meters, where the wood scale reads %MC at 5 to 30%, and non-wood materials' %MC is read on a relative scale of 0 to 100%.
Pin-less moisture meters are commonly used to determine moisture content on a relative scale of 0-100% in concrete sub-floors and flooring prior to laying a wood floor or other decorative flooring surface. Other common uses for a pin-less moisture meter for identifying possible moisture buildup behind bathroom/shower tiles, under vinyl flooring and other finished surfaces, as well as to determine if water-borne finishes are adequately dry prior to second application.
Pin-less moisture meters are capable of reading up to a typical depth of 3/4" or 1" into a subsurface. These are useful for detecting problem moisture buildup where visual indicators are nonexistent.
Pin/Pin-less/All-in-One Moisture Meter
A third and possibly more useful moisture meter would be a pin/pin-less/all-in-one moisture meter. This type of moisture meter utilizes both methods for measuring %MC in surfaces. Because this type of meter offers the option to measure moisture content in substrates using both methods of reading moisture, one meter may be able to identify problem areas and then also be used to pinpoint the exact location where moisture damage or buildup is occurring. Essentially, this type of meter would utilize the same scales of %MC for wood and non-wood substrates and allow the end user the versatility necessary for a full inspection in determining areas where moisture is an issue.
Ideally, due to its diversity, this type of meter could be utilized by the flooring specialist, IAQ specialist, general contractor and home/building inspector.