Moisture is a natural variable which affects numerous industries and occurs in many different types of materials. A Moisture Meter is an essential tool because it allows you to precisely quantify the level of moisture in a material you are working with. Excessive moisture can cause big problems down the line which can be costly to repair - if left unmonitored, moisture can cause dangerous mold growth, flooring failures, inventory product losses, and even professional liability issues.

Regardless of the material being measured or type of moisture meter used, the primary measurement for these tools is moisture content (MC). This measurement is often restricted to a particular scale. Measuring moisture in wood is very common – a typical scale range for a wood moisture meter is 7-20% MC, meaning the meter can detect moisture content from 7 to 20 percent in a piece of wood. Different meters will have different scales for different applications and materials.

Pin-Type

A pin-style moisture meter typically has a pair of metal probes or pins that penetrate below the material’s surface to read the moisture content. Overall, this method is more accurate than pinless measurement. Pin-type meters measure using an electric current – the current is sent between the two pins and the meter can tell how much water is in the material by how much current travels between the pins. Due to this measurement principle, testing a small area with a pin-type meter won’t give an accurate reading for the entire piece of material. Taking several readings along the full width and length of your material is recommended.

For applications like woodworking, you might think a meter like this would damage the surface of your wood – however, measurement pins are typically extremely small. Unless you were looking for the pin holes, you likely would not notice them. An advantage of these meters for woodworking applications is that you can easily use the small pins to take readings on any wood no matter what the shape, size or degree of roughness.

Another thing to keep in mind with pin-type meters for wood is that uninsulated pins will measure the wettest layer of wood they come in contact with, regardless of how deep the pins penetrate the material. This can throw off your readings if the outer layer of the wood is especially moist. Meters with insulated pins are available to get around this – these pins only measure the MC of the wood at the pin tips.

Pinless

A pinless moisture meter provides a non-destructive, non-invasive method for measuring moisture content. That said, this method is slightly less accurate than pin-type measurement with additional variables to take into account. A pinless meter will have a sensor pad on the device for taking readings. This sensor projects an electrical field into the material - the meter can sense changes in the field caused by moisture, then converts the change to a moisture content reading.

While this method provides a faster and less destructive way to measure the MC of a large piece of material, it does require that the sensor pad be in good contact with the material for accurate readings. For woodworking, this can sometimes be a frustrating issue to deal with if your wood is not perfectly flat. You must also be able to hold the sensor to a large enough area of the wood – most pinless meters have sensors that are too big to read the edge of a 4/4 board.

One other issue to keep in mind with pinless moisture meters is that these tools can give incorrect readings if influenced by surface-level moisture. In some cases, the reading that the device gives you may be reflective of moisture build-up on the surface rather than the interior of the material.

All-in-One

All-in-one moisture meters are powerful tools because they give you great versatility. These meters effectively eliminate all the drawbacks of each individual meter type by giving you the option to use either type at any time. Other interesting combination meters are available as well which incorporate thermal imaging cameras, relative humidity sensors, temperature sensors, and more. The only real drawback here is that these meters typically cost much more than meters which can only perform one type of measurement.

Wood

Moisture measurement is extremely common when working with wood. Meters for this application can be either pin-type or pinless. An important feature to consider with moisture meters designed for use on wood is the measurement range of the meter. As mentioned above, a typical scale range for a wood moisture meter is 7-20% MC. For certain applications like woodworking and furniture manufacturing, you will want to make sure your meter can measure on the low end of the scale (around 5%). Make sure to check what scale range you need before making a purchase.

Another consideration which is unique to wood moisture meters is species and temperature correction. Temperature and wood density can influence the readings given by your moisture meter, causing inaccurate measurements. To address this, most manufacturers include charts to guide you when adjusting for specific species and temperature variations. This is especially true for pin-type meters since these tools are more sensitive to temperature variations than pinless meters. Higher-end pinless meters will have built-in species correction and possibly built-in temperature correction as well.

If you plan to use a pin-type moisture meter for a woodworking application, keep in mind this rule of thumb for measuring MC in wood with a pin-type meter - the average MC of a board can be found at a depth equal to 1/5 to 1/4 the thickness of the board. Following this rule, a 1-1/2-inch thick board will require pins that are at least 5/16-inches in length.

Concrete

Concrete moisture meters are used to measure moisture on a limited area of the top surface of a concrete slab. These meters are also available as pin-type or pinless. Typically, these are used for conducting “relative only” spot checks on the concrete. Meters like this are not considered accurate enough for documenting relative humidity (RH) as required by groups like ASTM International (American Society for Testing and Materials). To test to these standards, you would need a special meter which can perform RH tests to determine a concrete slab’s RH at a specific depth. ASTM F2170 Standards provide specific requirements and procedures when performing RH tests for compliance purposes.

Building Materials

Moisture meters designed for testing building materials will often be able to test multiple materials. These materials can include sheetrock, ceramic tile, plaster, linoleum, mortar, brick, and more. As with wood moisture meters, these meters will have specific measurement scales for each type of material – be sure to check this before purchasing. These meters typically do not provide specific MC percentages as they are meant to provide only a relative MC reading for comparison purposes. This can help to identify problem areas in a building where moisture might be an issue. These meters are also available as pin-type or pinless models.

Soil/Hops

Soil moisture meters are primarily pin-type meters with a larger pin probe for reaching down into the soil. They give a measurement of the moisture content of the soil being tested. This can be an essential tool for agricultural industries and gardeners. Specialized meters for this application are also available which incorporate other measurement functions like temperature, soil Ph, and more.

Moisture meters for hops and hay also fall into this category – there are meters available to measure the moisture in stored grains like these to prevent moisture issues which can result in fungi, sprouting, and insect infestations.

Paper/Cardboard

For paper-based industries, a moisture meter helps ensure stock is kept in suitable conditions to prevent any damage. This can include regular paper as well as other fibrous wood-based products like cardboard. Similar to other moisture meter types, these meters are also available in pin-type and pinless versions.

Infrared

This category of moisture meter provides additional capability over standard meters by incorporating thermal imaging technology. This allows you to measure the radiant heat energy of a scene – while it won’t show moisture measurements, it will show you colder areas of a scene which could indicate water damage, mold, or other moisture-related issues. This can be very helpful to scan a large area quickly and identify any possible problem areas for deeper inspection later on.

FLIR, one of the world’s top thermal camera manufacturers, offers several thermal imaging moisture meters. Coming from FLIR, you can be confident that the thermal imaging capabilities of these tools will be unmatched. Plus, each unit also incorporates pin and pinless moisture measurement for 9 material groups so you can scan an area and do in-depth checks with only one meter.

Measurement Scale/Moisture Content Range

As mentioned above, the measurement scale is an important consideration for many material types but especially for wood. You should have an idea of the moisture content range you need and check it against any meters you are considering purchasing. A range of 7-20% MC will be suitable for most general applications concerning wood, but special applications might need a higher or lower range. Meters will go up to 30% MC for wood, but it isn’t possible to go higher as there is too much moisture in the wood. Meters will also go as low as 5% MC for wood but lower than this isn’t possible because there isn’t enough moisture to get a measurement.

Species/Temperature Correction

This consideration really only applies to wood. As mentioned above, temperature and wood density can influence the readings given by your moisture meter, causing inaccurate measurements. To address this, most manufacturers include charts to guide you when adjusting for specific species and temperature variations. This is especially true for pin-type meters since these tools are more sensitive to temperature variations than pinless meters. Higher-end pinless meters will have built-in species correction and possibly built-in temperature correction as well.

Multiple Materials

Many moisture meters available today incorporate measurements for multiple material groups. These can save time in the field and space in the tool bag since you only need one meter for multiple measurements. Before purchasing, the material groups a meter can measure should be one of your main considerations.

Pin Length

This is an important consideration for wood moisture meters which use pin-type measurement. The rule of thumb for measuring MC in wood with a pin-type meter is that the average MC of a board can be found at a depth equal to 1/5 to 1/4 the thickness of the board. A 1-1/2-inch thick board will require pins that are at least 5/16-inches in length. Following this rule, 1/2-inch pins will work for wood that is 2-inches thick.

Minimum Sample Size

This feature concerns pinless meters. A pinless meter has a minimum sample size which is related to the size of its sensor plate. The entire plate must be touching the material under test. For woodworking, this could eliminate this type of meter for your application – as an example, a meter with a 2 in. x 2 in. sensor plate can’t be used on a board that’s only 1-1/2-in. wide.

Display Type

There are various different display types available for moisture meters. Today, options include analog, LED, digital LED and digital LCD. This is really your preference – you might find you like the operation of an analog display, or that you need features like data hold which come with many moisture meters featuring digital displays. The resolution of a digital display is also important, with higher-end meters providing smaller data increments up to 1/10 percent.