Moisture meters are an integral part of doing business for many industries, particularly those that frequently work with wood as a construction material. Over the decades that our company, Delmhorst Instrument Co., has been in operation, we have received numerous questions about moisture meters from many people, including experienced professionals and first-time users alike.
Today, we wanted to address some of the most frequently asked questions that users have about wood moisture meters. Some of these questions come from those who are just looking into getting started with wood moisture meters, while others are from more experienced users who are looking for detailed tips:
Question #1: Why Should I Use a Moisture Meter for Wood?
This is perhaps the most frequently asked question among first-time users of moisture meters. While specific answers to this question may vary by your industry, such answers generally have to do with quality.
With a moisture meter for wood, you can accurately assess a given sample of wood’s likelihood to experience problems such as cracking, shrinking, splitting, mold growth, and more. When the moisture content of wood materials is too high (or even too low, in some cases), the quality of the final product will be affected.
Using moisture meters helps you to ensure that the moisture content of the wood materials that you are working with are in the right %MC range for use, avoiding callbacks at a later date.
Question #2: What are the Different Types of Wood Moisture Meters?
While there are countless models of moisture meters on the market, with new ones coming out all of the time, they fall into one of two categories based on their operation:
Pin-type moisture meters use two (or more) electrodes to penetrate wood materials to get a reading of that material’s %MC using the principle of electrical resistance. In a two-pin meter one pin emits an electrical current, and the other receives the current, with the meter interpreting how much resistance there was to the current. Since wood is an insulator and water is a conductor, the less resistance there is to the electrical current, the higher the moisture content of the wood.
Pinless meters, on the other hand, use electromagnetic radio waves to scan the sample of wood below the meter’s scanning plate. These meters are sometimes called non-invasive moisture meters, because they do not have to physically penetrate the surface of wood materials to get a reading.
Question #3: Which Type of Moisture Meter is better?
Right after asking what the different kinds of moisture meters are, most people also want to know which one is the best type to use. The answer largely depends on the type of work you’re doing, the dimensions of the wood material you’re working with, whether or not leaving pinholes in the material is an issue, and your personal preferences.
Pinless meters are quick and do not damage the surface of the material being scanned. Pin meters, on the other hand, can give you more specific information about the distribution of moisture in wood materials.
Many professionals use both types of meters in their work, switching between the two as necessary.
Question #4: What’s the Right %MC for Wood?
The answer to this question changes depending on the final use of the wood and where it is going. For furniture and flooring applications, most wood should have a %MC somewhere between six and eight percent. However, some areas of the U.S. may require drying to different %MC levels.
Question #5: How Do I Determine the Distribution of Moisture in a Board?
To determine the distribution of moisture in a board, you’ll want to use a pin-type meter with insulated pins (non-insulated pins can be used, but insulated pins make this easier).
First, take the pins of the meter and gently push them into the material to be tested. Take a reading in the “shell,” or outer, layer of the board. After the reading, push the pins in increments of 1/16”, taking new readings as you go. By noting the moisture readings of the board at different depths, you’ll have a strong indication of the distribution of moisture in the board.
Why not use a pinless meter? Because, pinless meters give you a reading of moisture for the entire area and depth for which they scan in a single number, there is no way to separate out the depth at which the moisture is present.
Question #6: Does Temperature Affect the Accuracy of Meter Readings?
The short answer is yes, but usually to a very small degree in pin-type meters. As wood’s temperature increases, its electrical resistance decreases, causing a rise in the indicated %MC for that sample. For in-field conditions, if the temperature of the wood sample being tested is between 50° F (10° C) and 90° F (32.2° C), there is no need to correct reading results for temperature.
When measuring wood materials that are outside of these temperature values, and the meter itself does not have a built-in temperature correction, you can use a temperature correction chart to find the correction (Delmhorst supplies these with every moisture meter).
Pinless meter readings do not measure electrical resistance, and as such their readings are not affected by the temperature of wood unless the sample is completely frozen.
Question #7: How do I Correct Readings for Different Species of Wood?
With both pin and pinless moisture meters, the species of the wood will affect the reading you get. For pin-type meters, the difference in readings is caused by the fact that different species of wood have different inherent electrical resistance properties. For pinless meters, the specific gravity (SG) of the wood influences the reading results.
Each moisture meter is typically calibrated using a specific species of wood, such as Douglas Fir or oak, which makes the meter accurate when measuring that type of wood, but less accurate for others.
In general, there are two ways to correct readings for a given species of wood:
Use a species correction chart from the meter’s manufacturer.
Use a meter with built-in species corrections.
Using a meter with built-in corrections is generally easier and faster than referencing a manual and doing the math yourself.
To learn more about moisture meters, check out our free Moisture Meters 101 guide at the link below, or read our FAQs page.