Anyone who has sold hardwood flooring for any period of time eventually asks this question:
How do I choose the right moisture meter?
The variety of moisture meters on the market and technical expertise required to properly use one can make it very confusing.
But, we have great news: it doesn’t have to be confusing!
First, it is important to understand the nature of wood and why a moisture meter is needed. Wood is hygroscopic. This means that wood will reach an equilibrium moisture content with its environment.
If the environment is humid, wood will gain moisture and reach equilibrium. If the environment is dry, wood will dry to reach equilibrium. Because the greatest comfort level in homes is between 35-55% relative humidity, wood floors are dried to an average moisture content that is at equilibrium with that humidity range.
It is for that reason that wood floors are dried to a range of 6-9%. That is the equilibrium range of wood at 35-55% relative humidity.
The need for a moisture meter then is two-fold.
- It can prevent claims by verifying the moisture content of wood and that it is appropriate for the environment in which it is being installed.
- It is necessary to help determine why a floor may have failed.
Types of Moisture Meters
There are two primary types of moisture meters: pin, and pin-less. Delmhorst Instrument Company does a great job describing the difference in meters and other meter resources. Pin meters use pins to penetrate the wood fibers and measure the electrical resistance in the wood. Water is the electrical conductor and with a properly calibrated meter, moisture content can be calculated. Pinless meters use radio frequency and based on the specific gravity of the wood species, moisture content can be calculated.
There is a perception that pin meters are more accurate than pin-less. In a lab, this may be technically true within a very small, standardize scientific test sampling. In practice, we have found pinless meters to be more accurate for the average needs of the wood flooring customer. With pin meters, pins must be perfectly straight in order to be technically accurate. Once pins are bent, numbers begin to skew. Since the pins must be forcefully penetrated into wood, the pins will begin the bend in the first measurement. Additionally, pin meters only measure the space within the two pins. It can only give a very accurate specific moisture measurement in a tiny sample. Lastly, pin meters require a person to damage the flooring, and for this reason, fewer measurements are typically taken on a floor.
Pin-less meters give a more average measurement under the area of the meter. Pin-less meters are also very easy to unintrusively measure a very large sample size of flooring. A person can measure a very large area of flooring in a short time without damaging any of the boards. For this reason, we believe that pin-less meters provide a more accurate overall moisture reading of the entire wood floor. We recommend that all flooring installers and resellers have a pin-less moisture meter.
What to consider when buying a pin-less meter
There are many manufacturers of moisture meters. As you evaluate what type of meter you buy, we consider the following factors important to consider.
- Species Correction: The average moisture meter is calibrated to measure moisture content of Douglas Fir wood species. For a pin-less meter, Douglas Fir has a specific gravity of .51. If a species of wood has a different specific gravity than Douglas Fir (almost all wood species have a different specific gravity), it will require a correction table to know what the moisture content is. Better meters have internal species correction settings to accurately read the moisture content of the flooring in question. Charts are provided to enter the specific gravity for the species, and an accurate reading can be taken from the meter. Lignomat has the most complete listing of species that we’ve found in the industry.
- Depth of Measurement: The average pin-less meter measures at a ¾” depth and provides an average reading of the MC across that depth. Some meters provide a variable depth reading. The most common being the option to measure at ¾” and ¼” depth. This helps the inspector to evaluate if the bottom or top of the board has more or less moisture content. It also allows for measuring moisture content of engineered flooring veneers.
- Manufacturer Species Support: In my experience, and this is very disappointing, most moisture meter manufacturers provide little to no support for exotic species of flooring. Since most meters are calibrated to Douglas Fir, it is very important to know how to correct the reading to the specific species of flooring. Most manufacturers do not provide any support for correcting the reading to species like bamboo, Brazilian Walnut, or Acacia flooring. The average user is left to decipher the moisture content of the species with no technical support. It is for this reason that we recommend and primarily use Lignomat meters within our company. Lignomat routinely tests and provides correction settings for all kinds of species of flooring, and will provide needed technical support when asked.
- Distributor Technical Support: We recommend the use of the Ligno-Scanner SDM moisture meter in our locations. In addition to its superior species correction tables, variable depth of measurement and unparalleled species support, having customers use the same meter that we employ allows us to provide better customer support. If a customer is at a job site and is measuring a hickory floor and is receiving puzzling readings, we can take the same meter, use the identical settings, and measure the same species in our shop. This allows a baseline comparison to confirm readings and provide greater confidence to a reading.
While there are numerous meters and needs in the industry, in our experience, the average hardwood flooring professional needs the ability to measure a variety of species of flooring across different types of construction. In addition, the ability to measure a large sampling of boards in different areas of the home is important. Technical support and confidence in the process is paramount. It is for that reason that we primarily recommend the Lignomat SDM meter for our customers to purchase. We believe it is the clear leader in the industry in the four criteria for choosing the right meter, and any of our locations can provide this meter for you.