3 Tips for Using a Moisture Meter for Drywall

Posted by Tom Laurenzi on Feb 22, 2019 10:00:00 AM

Gypsum, aka “drywall,” is a very popular material for use in the construction of homes and offices. The material is noted for its strong fire-resistant qualities. However, drywall is also known to be easily damaged by moisture compared to many other building materials.

This is, in part, because drywall is extremely porous, readily absorbing and retaining moisture. If the moisture content (%MC) of drywall exceeds even 1%, then the drywall can be considered “moisture-compromised” and in need of either drying or removal depending on whether mold has begun to grow.

Even greenboard, the “water-resistant” drywall, will be damaged by moisture if it gets past the green, water-resistant paper covering that gives greenboard its name. This is because the majority of greenboard’s water resistance comes from the paper covering, not the drywall itself.

Because of how susceptible drywall is to damage from minute amounts of moisture, it’s important to accurately assess the amount of water present in drywall—even when said moisture is in minuscule increments. Using a moisture meter for drywall is one of the fastest ways to test moisture in drywall. However, not just any moisture meter will do. To get accurate results, the moisture meter should have a specialized gypsum/drywall scale mode.

To help you find the right moisture testing device and get the best results from drywall moisture checks, here are a few tips for how to use drywall moisture meters:

Tip #1: How to Use Drywall Moisture Meters

Finding the Best Moisture Meter for Drywall

Ideally, you’ll want a specialized device to use as a moisture detector for drywall. This is where drywall moisture meters are useful. Drywall meters, like Delmhorst’s BD-2100 and TECHCHECK PLUS, are pin moisture meters that have a special drywall scale setting designed to get accurate readings of moisture in drywall as low as 0.1% MC.

These incredibly precise drywall scale moisture readings are valuable for professionals who need to know exactly how close gypsum boards are to being moisture compromised or track dry-out progress of a piece of drywall.

When looking for a moisture meter to use for testing drywall, some considerations include:

  • Whether or not the pin moisture meter has a gypsum scale.

  • The moisture detection range of the meter’s drywall scale setting—a drywall moisture meter should be able to accurately detect very small amounts of moisture (such as 0.1% MC).

  • The length of the pins. Most drywall is very thin, so long pins aren’t usually necessary—unless there’s a need to test the insulation or other building materials behind the drywall for excess moisture. If testing behind drywall to find a moisture intrusion source, extended-length pins are a must.

  • Additional scales for other materials—most professionals work with more than just drywall, so having a moisture meter with the ability to test other materials using different reading scales is a must.

Why are the best drywall moisture meters typically pin moisture meters and not pinless ones? That’s largely because pinless moisture meters always scan to a fixed depth. If the drywall is too thin, then the meter will scan the space behind the drywall, which throws off the moisture meter’s accuracy. Pin moisture meters use the drywall to complete a circuit, so they avoid false positives from moisture in the air.

Tip #2: How to Use Drywall Moisture Meters

Identifying Moisture-Compromised Drywall for Testing

In many cases, if there is significant moisture in a gypsum board, then there will be obvious external signs of it. For example, a simple visual inspection can be made to spot discolored or visibly crumbling drywall, or a musty odor can indicate a problem with mold growth.

While not the most scientific check, these visual and olfactory warning signs can help you narrow down the area of the drywall that needs testing. However, both of these warnings indicate that moisture has gone unchecked in the drywall for a significant amount of time, meaning it’s more likely that the problem may have spread to other materials.

Once you’ve identified roughly where the moisture-compromised drywall is, you can start taking readings with your drywall moisture meter. The process for making a test is simple—just make sure the meter is in its drywall scale mode, push the pins into the drywall, and push the button to take a reading.

With moisture-compromised drywall, it’s necessary to take multiple measurements to determine where the moisture-compromised material ends so it can be marked for tear out or dry out as needed. If mold is growing in the gypsum, best practices often recommend removing a buffer zone of at least 12 inches around the affected area.

Tip #3: How to Use Drywall Moisture Meters

Speeding Up Drywall Testing

When using a pin moisture meter for drywall, you may be able to speed up testing by using a nail and some ductile wire. Here’s how to use a drywall moisture meter with a nail and wire:

  1. Tie one end of the wire to the nail, ensure there is smooth contact between the wire and the ductile wire.

  2. Drive the nail into the wet area of the drywall.

  3. Tie the other end of the wire to one of the meter’s electrodes/pins.

  4. Punch the pin that isn’t connected to the wire into the wall and take a reading—keep doing this while making a full circle around the nail.

This helps you quickly identify the boundaries of the wet area and may help trace the origin point of the moisture.

Using a Moisture Meter Without a Drywall Scale

If a drywall moisture meter isn’t available, then testing can be done using a reference scale moisture meter. However, it is important to note that the readings you get with a reference scale test are qualitative, not quantitative—you’re getting a relative approximation of the amount of moisture present in the drywall, not an exact figure.

When using a reference scale moisture meter for drywall testing, any significant amount of moisture would mean that the drywall is moisture-compromised. However, it is important to first test a piece of drywall you know is completely dry. This gives you a point of comparison that lets you know what “dry” looks like in that situation. For example, if a completely dry piece of drywall reads 20 on a 0-100 reference scale, then you’d know that other readings of 20 are probably indicating dry gypsum too, while a reading of 30 is probably wet drywall.

For the best accuracy, however, it’s recommended that you use a moisture meter with a proper drywall scale setting when testing gypsum-based materials.

Need a moisture meter for drywall? Check our Dealer Locater to find a Delmhorst distributor near you!

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Topics: moisture meters