Moisture Testing in Wood Floors: A Manufacturer Roundtable
Testing the moisture content in hardwood flooring is vital to ensuring the product has acclimated and won’t cup, crown or otherwise fail. According to manufacturers of moisture testing meters, too many installers and contractors skip this important step and roll the dice on owning the cost of the job. We asked several manufacturers to share their answers to some common questions about moisture testing protocols and products.
What are the steps to measuring moisture in both solid and engineered hardwood flooring?
Grete Heimerdinger, vice president, Lignomat: “Measurements with any moisture meter, whether pin or pinless, are accurate when corrections for the wood species have been applied. This is easy for solid hardwood floors, because there is no question about the correction settings for the wood species. The installer can use the correction setting given by the manufacturer of the moisture meter.
“When dealing with engineered floors, there are usually at least two materials involved: the solid wood of the wear layer and the materials of the core of the floor plank. If they have the same correction factor, measurements are easy. The entire floor plank can be measured with the solid wood correction setting.
“However, often the correction factors are different between wear layer and core material. A good solution for measuring engineered floor planks is the dual-depth meter from Lignomat. The installer can measure the wear layer with the appropriate correction setting and get an accurate moisture percentage for the wear layer. Then that moisture percentage can be used to determine the correction setting for the entire floor. Once these two correction settings have been established, this type of floor can be measured with those correction settings.
“If you know the moisture percentage of one sample board of the engineered floor planks, you can always experimentally find the right correction setting, which gives the closest moisture percentage. After the right correction setting has been established, all floor planks of that type can be measured using that correction setting.”
Jason Spangler, flooring division sales manager, Wagner Meters: “With a solid material, you are only dealing with variations of nature, i.e. geographical area of growth. With engineered products, you are dealing with various configurations and materials utilized to provide a durable flooring product. Although the entire system is ‘wood,’ it becomes increasingly more difficult to determine how to measure the floor or which part to measure. Do I test the ply core, the veneer or both? What setting do I use for the core? What species is it? What about the adhesive—does that affect the readings?
“With a solid, you should first utilize a thermo-hygrometer to determine the ambient relative humidity and temperature of the environment where the flooring will be installed. To ensure the most accurate acclimation of the floor, this environment should be the same as when the space will be occupied. Obtaining this information, you can now calculate equilibrium moisture content. This calculation becomes your MC% (moisture content percentage) ‘bullseye’ for ensuring the wood is completely acclimated. Determine the proper setting for your meter and begin testing.
“With an engineered product, you should first refer to the manufacturer’s guidelines for acclimation. Some manufacturers are very specific about the process and time requirements. From a meter standpoint, in our opinion, you are best to determine what material the core of the product is made of and adjust your meter to that species setting.”
Andrew Rynhart, CEO, Tramex: “Solid hardwood is a homogeneous material which has been tested extensively for moisture and as such there are calibration curves for most wood species in the world. Engineered flooring is a combination of different types of wood and adhesive holding it together, so depending on where the reading is taken the results could be from the real wood top layer or the ply and adhesive.
“When testing a hardwood floor with a pin-type moisture meter, a calibration curve can be used to get accurate moisture measurements. If using a non-invasive meter, it is advisable to make sure it is possible to adjust for the density of the wood to get more accurate results.
“When testing an engineered floor using a pin-type meter, it is possible to take measurements in the top layer where species adjustment can be used to get accurate readings. When using a non-invasive meter it is a good procedure is to keep a sample of the flooring in an environment known to have a stable temperature and RH (relative humidity). This can be used to calibrate a meter to the correct setting.”
Paul Laurenzi, vice president sales & marketing, Delmhorst: “The biggest difference between testing moisture content in solid vs. engineered flooring is when testing engineered materials, it’s important to identify the different layers and isolate any impact that glue might have on moisture readings.
“We normally recommend using a hammer-type electrode with insulated contact pins for testing engineered flooring. Insulated contact pins read only at the uninsulated pin tips, allowing the flooring professional to drive the pins at different depths, noting differences between the top wear layer and the core in the engineered floor.
“The uncoated tips also allow the contractor to identify glues lines. This is done by touching the top layer, glue lines and the core. If the glue reads the same as the other material, then it has no impact on moisture readings. Some installers prefer using non-insulated contact pins on engineered materials because the tip of the insulated pin is thicker in diameter and is sometimes too large to differentiate between the layers and glue.
“When testing solid materials, use of non-insulated pins is sufficient as long as the wood is being tested prior to installation. The typical non-insulated contact pin penetrates 5/16” into the material, which is adequate for hardwood flooring and subfloors if they are independent of each other. However, if it’s necessary to check the flooring after installation, the hammer-type electrode is a must because it is the only way to identify the exact location of moisture in the subfloor.”
How many times should a floor be measured for moisture?
Heimerdinger: “It may be many times during acclimation. The first measurements should take place as a board is taken out of the package. Mark the location of the measurement on the board and take notes of the moisture percentage, the moisture meter correction setting and the measuring depth. During acclimation those same locations should be measured and the values compared.
“The board is totally acclimated if no more changes in moisture content occur over time and if the moisture percentage is in accordance with the subfloor and the average relative humidity conditions for the location of the installation. In case of any questions, the installer can follow the instructions from the floor manufacturer.”
Spangler: “Referring to the National Wood Flooring Association (NWFA) guidelines is always recommended. They state for finished floor product, 40 tests per 1000 sq. ft. of material. For wood subfloors, they recommend 20 tests per 1000 sq. ft. of material.”
Rynhart: ”It depends on the stability of the ambient temperature and RH, which needs to be monitored.”
Laurenzi: “Although there is no hard fast rule as to the number of readings to be taken, a generally accepted guideline is to take 20 readings per 1,000 sq. ft. of flooring and then to average the results.
“In addition to the number of readings, it is extremely important to allow wood to be brought to equilibrium before installation. This is achieved by delivering the wood to the jobsite and measuring the moisture content of it and the subfloor. Continue to take readings on both materials until there is no further change in moisture readings and until the subfloor is within 4% MC of the flooring, maximum. For wide plank flooring, a 2% difference between the floor and subfloor is recommended.”
What are some common mistakes installers and contractors make during these tests?
Heimerdinger: “When using a pinless meter, the installer has to hold the meter against the floor planks and push slightly down. As far as I know, this is the same for all pinless meters. It is not correct to place the pinless meter on the floor and take the measurements without putting slight downward pressure on the meter.
“The next common mistake is not to use the right correction settings for the wood species or the materials to be measured. This could be forgetfulness or not checking the correction setting. Either way, if it has become a practice to write down the species setting for each measurement, the oversight becomes obvious quickly and can be corrected. As long as the wood species and its correction setting are known during measurements, the moisture meter manufacturers should be able to find the correct moisture percentage.”
Spangler: “Number one is doing no moisture testing at all. Number two is not acclimating [the hardwood] long enough in the correct environmental conditions.”
Rynhart: ”It is important to compensate for the wood species to get correct measurements. If the wood is stored in a cold or warm environment it may be necessary to use a temperature adjustment to get an accurate reading.”
Laurenzi: “The biggest mistake a contractor can make when installing a wood floor is to not use a moisture meter. Some estimates indicate that moisture-related issues account for $1.8 billion in flooring failures and claims. Although the scope of these losses would indicate that a moisture meter is a ‘must-have’ tool, we still talk to many flooring professionals who don’t use one.
“That said, there are some basic things to keep in mind when performing moisture tests. One of the most common mistakes flooring professionals make when checking moisture content is to not make a species correction. Most pin-type moisture meters are calibrated on Douglas fir, so when testing other species, it is important to refer to a correction chart, or if the meter has built in species correction capabilities, set the meter for the species being tested.”
When should one choose a pin meter or a pinless meter?
Heimerdinger: “In the flooring industry both pin and pinless meters are used with great success. Many floor installers have both meters and use as appropriate. For an installed floor or a floor inspection, pinless meters are often used because the floor will not show any pinholes. Even if in theory nobody would ever see the pinhole, homeowners often reject the use of pin meters because the pinholes may be obvious.
“A great pair of tools for any floor installer is the thermo-hygrometer and moisture meter. First you measure the moisture of the wood; then you take a hygrometer reading of the air. And lastly you compare the values to the EMC (equilibrium moisture content) chart, which shows the relationship between equilibrium moisture content and relative humidity and temperature.
Wood moisture and relative humidity are crucial factors for dimensional stability of wood. If wood cups, warps, shrinks, checks or delaminates, it always has to do with changes in wood moisture and/or relative humidity. No shrinking and warping occurs when equilibrium with the surrounding air has already been reached, which means the wood is not losing or absorbing any more moisture.
Spangler: “Pin meters are great for determining moisture gradients in cupped flooring where a pinless meter can’t sit flat on the board. Well-constructed pin and pinless meters have both proven to be highly accurate. With accuracy being equal, the question becomes which type of product do you feel the most comfortable using? At the end of the day, pick one and use it. The best meter is no help if it is never utilized.”
Rynhart: “Pin meters are generally less expensive and if made by a quality manufacturer, are more accurate. However, they are slower to use and leave holes in the wood that has been tested. The ideal is to combine the pin meter for calibration and pinless meter for speed.”
Laurenzi: “To quickly identify wet areas in floors, a pinless moisture meter is easy to use. They offer the convenience of testing a large area quickly, and help you determine if further testing is required in certain spots. A pinless moisture meter may also be used to determine if waterborne finishes are dry and ready for a second application.
“A pin-type moisture meter, on the other hand, is the best way to identify the exact location [of moisture] in subfloors. The key to finding hidden moisture is to use an electrode with insulated contact pins. Generally speaking either a pin-type or pinless moisture meter can be used prior to installation, but a pin-type meter with insulated pins must be used after installation if a claim is made.
“Whichever moisture meter a flooring professional chooses, it’s important to look at it as an ‘insurance policy,’ Moisture meters help keep contractors fully informed about the moisture level, minimizing the chance of defects, such as cracking, cupping and warping—avoiding costly callbacks.”