For a wood flooring installer, moisture can be the biggest obstacle to a job otherwise well done.
Even a small amount of excess moisture can cause warping, buckling, cupping, adhesive failure, unhappy clients, and costly repairs or replacements.
A long-lasting, great-looking floor requires thorough moisture management before, during, and after installation.
That’s why, for many flooring installers, the first tools they bring into the house or building are moisture meters. Installers know that materials below their target moisture content are not ready for installation.
The proper use of moisture meters helps you keep tabs on moisture content so you can keep it in check. Use your own data to confirm dryness instead of relying on someone else’s assumptions.
It’s like having a mini inspector in your pocket.
But aside from having the right tools, you also want to be sure you’re using them right and getting the most out of them. What type of moisture meters should you use? How do you know if you’re getting the readings you need? How often should you use them? What settings, modes, or functions do you use, and in what situations?
To get you all these answers and more, here’s a central source of information about moisture meter best practices for flooring installers like you. We’ll cover:
- An overview of the meters you’ll need
- How to properly use a wood moisture meter
- How to properly use a concrete moisture meter
Let’s start with a quick review of what we’re looking at.
The Basics: Your Moisture Meter Pairing
Both wood and concrete can look and feel dry on the surface, but still harbor hidden moisture deeper within.
That’s why you need good quality moisture meters on hand. Before you get started, you need to determine the true amount of moisture in the subfloor, whether it’s wood or concrete, and in the wood flooring itself.
We’ll discuss two types of moisture meters that are the most relevant for your work:
- Wood moisture meters: Use wood moisture meters to test the moisture levels of both the flooring material and the wood subfloor.
- Concrete moisture meters: While relative humidity (RH) testing is the correct method for commercial flooring projects, a concrete moisture meter plays an important role in RH probe placement and in residential flooring installations.
Proper Use of Wood Moisture Meters
The first step is to make sure you have a wood moisture meter that fits your needs as a trusted, professional flooring installer.
Choosing the Right Moisture Meter
The two types of wood moisture meters are:
- Pin-type meters: Pin meters use two sharp probes pressed into the wood to measure moisture between the pins. But, naturally, that leaves holes behind in the wood. These meters measure small areas. Taking multiple readings requires poking many pairs of holes, making “big-picture” views difficult.
- Pinless meters: These use electromagnetic signals to take moisture readings by pressing a plate to the flat surface of the wood. They work quickly, making it easy to take several measurements in different places. And best of all, they don’t leave any marks or damage behind.
Choose pin meters for irregular surfaces where a flat pinless plate cannot make proper contact. Some pinless moisture meter readings can be thrown off by surface moisture. In most cases, we recommend a pinless moisture meter as the best non-destructive way to test for moisture.
And it goes without saying that you’ll want a high-quality moisture meter with good reviews and a clear, thorough warranty. Surface appearance is misleading. Testing provides the only accurate measurement of the wood’s true moisture content. So you want a product that consistently gives accurate readings and has good customer support.
Preparing for Measurement
Now that you trust your moisture meter, you must use it correctly. This starts with preparing your materials and stabilizing the installation environment.
- Establishing consistent ambient conditions: Seal the workspace from the outdoors. Run the HVAC at “live-in” levels for two days before acclimating wood.
- Take preliminary moisture readings before you finalize ambient conditions. This gives you a precise timeline for how much drying or acclimation the wood requires before installation.
- Acclimation and drying time: Once ambient conditions are established, you want to have allowed adequate time for the flooring material to acclimate to its new environment. And if you’re installing over new construction, you want to make sure the subfloor has had adequate drying time as well. Use your moisture meter to check that these processes are proceeding as expected, or to help you determine if adjustments to the installation schedule might be needed.
- Calibration: Make sure the meter you purchased is calibrated and ready for use. Otherwise, the readings could be skewed and you could end up installing flooring over a subfloor that wasn’t ready, or you could end up installing flooring that wasn’t fully acclimated. Most high-end moisture meters will come with a calibration accessory so you can verify that it’s good to go. If in doubt, contact the manufacturer.
- Surface prep: Make sure that the floorboards and the surface of the subfloor are clean of dust or other debris before taking readings. Make sure that several different spots are prepped for testing so you can get a fuller picture of the wood’s moisture condition.
Taking Good Measurements
After preparations are complete, you want to make sure you’re getting the most accurate and useful moisture readings possible. Here’s what’s involved in getting the data you need before beginning the installation:
- Read the manual! Wood moisture meter settings and functionalities vary across brands and across models. You want to be sure you’re using your meter exactly as it’s designed to be used.
- Set the meter to the right species of wood: Make sure your meter is set to match the wood species of your flooring material, and of the subfloor if you’re installing over wood.
- Apply the right amount of pressure: For pinless meters, you want to be actively pressing the plate onto the surface of the wood. No need to exert a lot of force, but you do want to make sure the plate is firmly against the wood’s surface when taking readings. Just a couple of pounds of pressure is all that’s typically needed.
- Measurement depth: Some moisture meters have dual depth settings that allow for more thorough data. Other meters are designed to measure a specific depth, so you want to make sure you have a meter that will work well with the thickness of the wood you’re testing.
- Avoid metal, whether in the wood or underneath: Since wood moisture meters use electric frequency to take readings, they are sensitive to anything conductive. Wood with nails or screws in it can skew readings, and if floorboards are sitting on a metal table, you want to place the board elsewhere or hold it in the air to take your readings.
- Take multiple readings: To get a thorough, big-picture view of the moisture situation for both flooring and subfloor, you want to take several readings in several different areas. Check varying locations of the subfloor, and measure multiple floorboards from different parts of the stack, depending on how they were stored while acclimating.
- It’s likely that some parts have dried faster or more completely than others, and you want to know 1) if there are still areas of higher moisture, and 2) where those spots are. This makes it a lot easier to make the best decisions going forward.
- Note: This is another reason pinless meters are more helpful and practical for flooring installations. You need to be able to efficiently measure large areas without damaging the wood.
- Scan across the surface between two areas with different readings: Utilizing another perk of pinless moisture meters, you can more precisely determine the size and location of the areas with higher moisture. Start measuring at a lower-moisture location and keep the measuring plate against the wood while slowly moving it toward the area with a higher reading.
- If you get several varying readings in different places in the subfloor, this will help you determine the shape and size of the wetter area(s) and best determine what needs to happen next.
- This can also help in pinpointing the location of a potential moisture problem, such as a slow leak or a spot where moisture is somehow getting in from the outside.
Target Moisture Levels
For hardwood flooring, the ideal range of moisture content is between 6% and 9% while at room temperature (60–80 degrees Fahrenheit and 30–50% relative humidity). For engineered wood flooring, the range can expand from 6% to 12%. You’ll want to check the manufacturer’s recommendations.
However, the climate of the installation location does matter. You want to determine the area’s equilibrium moisture content (EMC), which you can look up on this USDA Forest Service chart. Then you want to aim for a moisture level that is an average of the high season and low season EMC.
What if the readings are outside the recommended range?
If your floorboards are found to be too dry (under 6% moisture content) or too wet (over 9%), it may just mean that a little more acclimation time is needed.
It could also mean that the ambient conditions of the installation area need to be adjusted. A few things you can do to help stabilize the environment might be:
- Increasing ventilation
- Using dehumidifiers
- Waiting. Outside weather can affect indoor conditions, or the indoor environment might just need more time to establish consistent temperature and relative humidity.
And as you make the necessary adjustments to the schedule or the ambient conditions, continue to take moisture readings often to keep tabs on the situation.
Tips and Troubleshooting
You’ve been following the directions to the letter—but what if you come across some readings that just don’t seem right? It’s good to get familiar with common issues or situations that could mess with the process of wood moisture testing. Here are some things to consider if you’re not sure what to make of the readings you’re getting.
- Take some baseline measurements: If a reading doesn’t seem quite right, test other areas you know to be dry to get a few controlled readings. If those seem off as well, there may be an issue with the meter itself, or with the meter’s settings.
- Calibration check: Did anything happen that could have affected the meter’s functionality, such as getting dropped, or something heavy falling on it? Or has it been put away for a long time without use? Use a calibration block to check the meter’s readiness, find the calibration information in the manual, or contact the manufacturer for instructions.
- Double-check the settings: Is the meter set to the correct species of wood? And is it set to the measurement depth you’re looking for?
- Double-check for metal and other disruptive materials: Could there be any nails, screws, or plates in the flooring or subfloor that could mess with the meter’s conductivity? Is the wood sitting on a metal sheet or table, or against a metal chair or stool? Is it sitting directly on a dense material like concrete?
- Environment check: Has there been any change in temperature or humidity in the installation area?
- Water check: Keep the meter dry, and don’t measure areas with visible surface moisture. Moisture meters detect hidden water that the naked eye cannot see. So they are not waterproof! And they are not designed to measure large amounts of moisture.
- Are you installing bamboo flooring? This type of wood flooring comes in three different forms (strand-woven, horizontal, vertical) and can require unique and specific gravity settings. Double-check the manufacturer recommendations for the flooring and check if the moisture meter manufacturer has different instructions for bamboo.
You’ll be able to sort out most moisture-measurement issues by going through the above list. But if you still don’t feel confident in the results your meter is giving you, it’s best to contact the manufacturer’s customer support for further instructions. In some cases, it might need to be sent back to the factory for recalibration.
Now let’s go over a concrete moisture meter’s ideal role in your floor installations.
Proper Use of Concrete Moisture Meters
In addition to your wood moisture meter, you’ll also want to have a concrete moisture meter on hand for when you’re installing over concrete subfloors.
While various concrete tests exist, electronic moisture meters are the most practical choice for residential installers.
And high-quality models can be used to follow the ASTM F2659 procedure for “preliminary evaluation of the comparative moisture condition” of the concrete.
But keep in mind that concrete moisture meters can only detect the moisture content up to ¾ of an inch below the surface of the slab. They are designed for comparative, or wet/dry analysis, rather than quantitative analysis. (For deeper, truer moisture readings, you’d need to use in-situ relative humidity probes, or discuss further testing efforts with the owner or contractor.)
But a good concrete moisture meter can tell you if a slab’s surface is still too wet for floor covering to be installed on top (and that also tells you that there’s even more moisture underneath).
It also detects areas of higher moisture content than other areas of a slab, since concrete doesn’t always dry evenly. So if some spots are wetter than others, more drying time might be needed, or possibly some adjustments to the ambient conditions. Finding higher moisture areas could also be an early indication of a potential moisture problem that needs further investigation.
Carrying a concrete moisture meter demonstrates your thoroughness as a professional installer. It shows that you’re on the lookout for anything that could negatively affect the quality of your work, or the satisfaction of your client.
Choosing the Right Concrete Moisture Meter
Accuracy is the number one quality you want in any kind of moisture meter. So you’ll want to do your research before you make this investment.
Always read up on warranties, check customer reviews, and choose a brand you trust.
Other features that can make a difference in ease of use are:
- Clear labels/symbols
- Easy-to-read display
- Durability
- Relative mode
- Alerts (since you may not always be able to see the display when testing, make sure you get a meter that alerts you when it detects higher moisture content)
Preparing for Measuring Concrete Moisture with a Meter
Here are the primary things you’ll want to check on before you start taking readings:
- In ideal conditions, once concrete has cured for 28 days, it takes roughly 30 days per inch of thickness for the slab to dry. So before you begin any work, you’ll want to at least make sure this timeframe has passed.
- Ensure the areas you want to test are smooth and clean. Bumps, pits, or cracks could affect how well the measuring plate contacts the concrete itself.
- Check that the meter is calibrated and ready for use, as per the manufacturer’s guidelines. Many high-quality concrete moisture meters come with a calibration block for verification.
- Make sure ambient conditions are stable and at the appropriate temperature and humidity for the needed measurements.
Taking the Most Helpful Moisture Readings
Once you’ve prepared both your meter and the surface of the slab for testing, you want to make sure you’re using the meter as effectively as possible. Here’s what’s typically involved in taking the most useful and telling measurements.
- Choose several testing locations to begin your scans. This will help you gather several comparative readings to work with.
- Place the meter flat against the surface of the concrete and check the first reading on the display before moving it around the slab. Make sure it’s in the appropriate testing mode.
- Record as you go, whether you’re writing the readings down, saving them in the meter, or recording them in an app over Bluetooth®.
- Also document the environmental conditions at the time of your moisture testing. This can be helpful for future reference, or in case any troubleshooting is needed later on.
Assessing Concrete Moisture Readings
For most flooring types, you’ll be looking for concrete moisture meter readings under 3.5% moisture content or under 75% relative humidity. Ultimately, however, you need to check the flooring manufacturer’s specifications as to what the flooring components can handle. Some will vary, and some may have additional details or requirements.
What if the moisture readings are too high?
If your meter is registering several wet spots, or if there’s a lot of variance in readings across the slab, it may need additional drying time (even if the 120-day timeframe for a 4” slab has passed).
For commercial jobsites, it’s recommended to consider additional methods of moisture testing so you can get a clearer, more comprehensive picture of the slab’s overall moisture condition. In-situ RH probes measure at a 40% depth. This gives you more accurate, actionable readings because then you know the long-term RH level the floor covering would be exposed to if it’s installed over the slab at that time.
Your concrete moisture meter will come in handy to help you determine the best places to insert the RH probes for further testing. When you take several surface readings in different areas of the slab, the spots that give higher comparative readings reveal where the probes will provide the most helpful moisture data.
If you cannot wait for drying, use a mitigation system to block moisture from reaching the flooring.
Tips and Troubleshooting
What if you’re not confident in the moisture readings your meter is giving you? What if something seems off?
Similar to what you’d do with your wood moisture meter, you first want to check the calibration.
- Calibration check: Did anything happen that could have affected the meter’s functionality, such as getting dropped, or something heavy falling on it? Or has it been put away for a long time without use? Most good quality concrete moisture meters will come with a method for verifying calibration. If not, check the manual or contact the manufacturer.
- Double-check the settings: Is the meter set to measure concrete? Make sure the meter didn’t accidentally get switched to relative mode.
- Check for irregularities with the concrete: Surface moisture or condensation will skew meter readings. So can the presence of metal, salts, or fine bits of debris on the surface. Check for signs of potential leaks or improper curing.
- Check for any recent changes in ambient conditions: Even if conditions are stable at the time you’re testing for moisture, you may need to check with the homeowner, building manager, contractor, etc., to see if there were any recent changes in temperature or relative humidity that could have affected the readings.
Moisture Meter Wisdom to Live By
For both your types of moisture meters, even if you get the top-of-the-line models from a manufacturer you trust, it makes a huge difference how carefully you use them.
To consistently get the most accurate and useful readings possible, it pays to fully familiarize yourself with the product and its warranty. Always use it as the instructions state, and don’t hesitate to contact customer service if you have any questions or concerns about its performance.
Adequate preparation goes right alongside knowing your tools like the back of your hand. No matter what material you’re testing, you always want to ensure that the surfaces you’ll be taking readings from are clean, clear, and free of irregularities or defects.
All in all, you want confidence in your moisture management so you can have confidence in your finished product.