How to Interpret Moisture Meter Readings on Different Scales

Posted by Tom Laurenzi on Apr 10, 2018 3:28:00 PM

Moisture meters are indispensable tools for professionals in many different industries, including restoration, contracting, farming, lumber production. However, moisture meter scales can create some confusion. An understanding of the different moisture meter scales will help users to make the most accurate and efficient use of these tools.

To help you better understand each of the different moisture scales, here is some information about each scale and how to interpret its readings.

The Reference Scale

Reference scale to read moistureThe reference scale is quite different from most other moisture measurement scales. Most reading scales are designed to provide a specific, quantitative measurement of moisture content (%MC) in a given type of material. However, reference scales provide a qualitative estimate of moisture in a variety of materials.

In many cases, a moisture meter’s reference scale will range from 0-100, but that reading should not be confused with a percentage. Some meters use a 0-300 reference scale, so readings taken on a reference scale often do not correlate with one another.

Some ways to use a moisture meter with a reference scale include:

  • Quick Pass/Fail Moisture Tests. Many professionals use reference scale meters to quickly determine if a given material is extremely wet or dry. By taking a “reference” measurement of a material sample known to be dry, it is possible to compare future reference scale readings to that reading.
  • Testing a Variety of Materials. The reference scale is not specific to any one material—so it can be used to check many different things. While readings aren’t in precise percentages of moisture content, they can be invaluable for getting a general indication of moisture in materials that might not have a specific scale.
  • Checking Available Moisture in Soil. Delmhorst’s KS-D1 soil moisture meter uses the reference scale (in combination with special gypsum sensor blocks) to monitor the amount of available moisture in soil. Farmers often use this to optimize irrigation schedules to save water or enhance crop quality.

The Wood Scale

The wood scale is, as the name implies, optimized for getting precise %MC measurements in wood materials. This scale is often used in the flooring, construction, lumber, and restoration industries.

Most wood moisture meters are calibrated to cover a range of 6% to 40% moisture content. However, this may vary slightly by model and manufacturer.

Moisture Content of Wood EMC Chart

Different species of wood may measure differently based on their physical characteristics, but the basic wood scale is generally reliable for most construction-grade lumber. Some meter manufacturers provide species correction charts or make meters with built-in species correction capabilities to allow you to correct readings for a variety of wood species.

The differences that may require a correction when testing different species of wood become even more significant when entirely different materials are involved. Thus, a wood-scale meter should not be used to measure concrete, drywall or other building materials.

When checking the %MC of wood, it is generally considered “safe” if its moisture content is between 8% and 11% in most parts of the U.S.

The Drywall Scale

With most moisture meters, drywall is measured using the reference scale and comparisons to dry materials. However, Delmhorst offers several moisture meters that are calibrated specifically for drywall.

This drywall scale is optimized for reading incredibly miniscule amounts of moisture—largely because gypsum is so sensitive to moisture. In fact, drywall must be below 1% moisture content to be considered structurally sound and free from mold or decay. So, Delmhorst’s drywall scale moisture meters can accurately detect moisture content in drywall to values as low as 0.1% or 0.2%.

Drywall scale meters are often useful for the construction, home inspection, and water damage restoration industries.

One surprising use for drywall scale meters is to check Gyp-Crete flooring. Since Gyp-Crete is primarily composed of gypsum (the stuff drywall is made of), meters calibrated for drywall are highly accurate for measuring moisture in Gyp-Crete as well.

Hay Scale

Hay moisture meters work by providing a percentage-based moisture content measurement of moisture in hay. These meters typically work best when measuring a haystack or bale because the hay will be more tightly packed. Generally speaking, the moisture content detection range of a hay meter is between 6% to 40%, though there are some meters that go higher or lower.

For farmers, distributors, or rangers, measuring moisture content goes a long way in protecting the quality of the hay and the safety of the person storing it. Just a few percentage points can mean the difference between a superior-quality feed and spontaneous combustion due to bales of hay being too moist.

Paper Scale

For those manufacturers who create the millions of tons of paper produced every year, a healthy moisture content is crucial. Before it becomes its final product, the wood for paper is first separated into useful fibers and waste material. Then, it is beaten into a pulp and mixed with other chemicals to enhance its color and other properties. The resulting slurry is poured onto a moving screen so excess water can be drained away. Once the paper is dry enough, it is pressed and dried again to create paper.

During each of these transitional phases, knowing the content of water in the material is necessary to ensure a top-quality paper product.

These meters are programmed for a paper scale and there are also specialized electrodes that are used to test the paper’s content. These electrodes roll with the movement of the pulp web on the moving screen so they are able to take continuous measurements without compromising the integrity of the fabric.

Whatever the material you’re working with, moisture meters offer an efficient, cost-effective way to ensure that the materials are dry enough to work with and to identify trouble spots. Using the right meter and the appropriate scale is critical to getting the most out of your moisture meters, regardless of your industry.

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