Why Flooring Installers and Inspectors Use Moisture Meters for Wood

Posted by PAUL LAURENZI on Oct 23, 2017 7:52:44 AM

When installing wood flooring, moisture is a constant concern. This is because wood is a hygroscopic material—it will gain or lose moisture until it reaches equilibrium with the surrounding air’s humidity and temperature.

So, why should flooring installers and inspectors use moisture meters for wood flooring?

Because of Moisture-Related Issues That Can Happen

If left unchecked, moisture issues can lead to flooring failures—ones that have cost the industry over $1 billion in claims. For example:

  • Excess Moisture Can Cause
    • Cupping
    • Crowning
    • Buckling
    • Edge lifts
    • Finish issues
  • Too Little Moisture Can Cause
    • Gaps between strips and at the ends
    • Surface checking
    • Noisy floors
    • Loose boards

So, it’s only natural to closely monitor moisture conditions in expensive wood flooring. And, moisture meters for wood are the go-to tool for any expert dealing with wood flooring. With a wood-scale moisture meter and a thermo-hygrometer, it’s relatively easy to determine if the wood flooring in a structure is at equilibrium moisture content (EMC).

First, the thermo-hygrometer should be used to check both the temperature and the relative humidity (RH) of the area. This information can then be plugged into a simple temperature/humidity chart to find the appropriate moisture content (%MC) of properly-acclimated wood.

Moisture Content of Wood EMC Chart.png

For example, the appropriate %MC value of wood in a structure at 70°F and 30% RH would be 6.2% MC. At that moisture content, the wood would be considered to be in equilibrium with its environment. Likewise, if the temperature were 80°F and the RH was 50%, then the EMC value of the wood sample would be 9.1% MC.

Once what the EMC value of the wood should be, then flooring specialists can use a moisture meter to get a quantitative reading of the floor’s moisture content to see if it’s close enough.

In addition to taking EMC into consideration, some adjustments may need to be made based on the species of flooring being tested.   In such cases, it might be necessary to contact the manufacturer of the moisture meter to see if they have a species correction chart.

Alternatively, if no species correction exists for determining EMC, it may be necessary to simply repeatedly measure the wood’s %MC over the course of a day or two in a controlled environment.  When the %MC measurement stops changing, then it is likely that the wood has reached EMC.

Making sure wood has reached EMC is crucial for preventing wood flooring failures that lead to wasted time, materials, labor, and call-backs.

How Many Moisture Measurements Should Flooring Installers Take?

At a minimum, installers should take 20 moisture content readings per 1,000 sq. ft. of subfloor, and 40 boards checked for every 1,000 sq. ft. of flooring. This is what’s necessary for a “good representative sample” per the NWFA’s guidelines.

Flooring Inspectors  may need to be even more thorough in their checks. If moisture is detected, they may have to take enough moisture readings to establish the outside edge of the damaged area—which will most likely take more than 40 readings per 1,000 square feet of flooring.

Comparing Moisture Meter Options

There are two kinds of wood moisture meters available to flooring installers: Pin meters that use electrical resistance and pinless meters that use electromagnetic waves to measure moisture as a percentage of the wood’s oven-dry weight.

Pin meters bring precision to moisture checks, and are often used to determine how deep in a sample of wood a moisture pocket occurs. Meters with insulated pins are particularly good for determining just how deep a moisture pocket goes. However, they leave pinholes in the surface of the wood—which is not an attractive option for flooring professionals!

Pinless meters don’t have to penetrate the surface of the wood to measure moisture These meters are sometimes called non-destructive moisture meters because they don’t have to damage the surface of wood flooring—so they’re often preferred for checking flooring moisture.

Many professionals keep both kinds of meters on hand—or use a 2-in-1 device that can be used either way. The pinless meter can quickly take readings in different places without damaging the floor, while the pin meter can provide more precise measurements of moisture in wood.

What Affects Moisture Measurements Other Than %MC?

There are a few different factors that can change a moisture measurement beyond the actual moisture content of the wood being tested. Each of these factors can affect pin and pinless meters differently:

  1. Wood Species. Both pin and pinless meters may be thrown off by different species of wood. In pin meters, this is because different wood species have different electrical resistance values. In pinless meters, this is because different kinds of wood have different specific gravities (SGs).
  2. Specific Gravity. Pin meters do not need to correct for SG (in fact, species corrections likely already incorporate SG as a factor alongside electrochemical differences in different wood types). Pinless meters do have to correct for the SG of the wood, and variations in SG within a wood species can be a concern.
  3. Wood Temperature. Temperature affects the electrical resistance of wood, so corrections may need to be made for pin-type meters. There is some effect on reading with pinless meters, but not nearly as pronounced, so corrections are rarely necessary. Also, temperatures rarely reach these extremes for interior flooring installations.
  4. Moisture Content Range of the Meter. Each moisture meter on the market has a set “range” over which it can provide accurate moisture meter readings. For most pin-type meters, this is between 6% and 25% MC, while pinless meters usually go as low as 5%. There are some models that can get measurements in wetter or drier wood, but this is the average. Outside of the meter’s range, moisture measurements become less accurate and work as a relative assessment of moisture. However, 6-25% is a suitable detection range for most jobs, as %MC values outside of this range often mean that the wood is compromised.

With a well-chosen wood moisture meter, flooring installers and inspectors can make sure that wood flooring is free from moisture-related problems that cost them time, money and lost reputation from call-backs.

Get to know more about using moisture meters for wood flooring in the Complete Guide to Measuring Moisture in Wood Flooring!

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Topics: Wood Flooring Flooring moisture meters

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