How to accurately measure moisture in Gypsum wall board

Posted by PAUL LAURENZI on Jan 30, 2016 1:05:00 PM

Gypsum is a popular material widely used in construction and known for its fire-resistant qualities. One of its more popular construction uses is gypsum board, also known as drywall or Sheetrock®. Though the material’s positive attributes outweigh the negatives, gypsum’s limitations are worth discussing.


For example, one issue is that the material is porous — meaning it can easily be damaged by moisture. With that said, proper management and monitoring of moisture in Gypsum is critical. Both Delmhorst’s BD 2100 and TECH CHECK PLUS have gypsum and drywall scales.

Interior wall mold

Drying Gypsum Board

Gypsum board that has absorbed excessive moisture may be safely dried, but ONLY if drying takes place before mold begins to form. Typically, there is a 24-48 hour window after having been exposed to moisture. However, once mold has begun to form, the contaminated areas must be removed and replaced.

Best practices suggest removing a buffer of about 12 inches surrounding the mold. This means having the right gypsum moisture meter on hand and taking accurate measurements are essential if problems are discovered in time to save tainted materials.

Testing for Moisture Damage

In some instances, after materials have been safely integrated into a structure, moisture damage can occur. Some of the most common ways this tainting occurs include storm damage and flooding, leaky pipes and faulty installation of windows, doors and flashing. Sometimes, materials might be damaged to the point where they need to be ripped out rather than restored. Knowing the gypsum’s moisture readings can avoid much costlier and more time-consuming problems later.

Testing for Moisture UNscientifically

Before using your moisture meter to determine the %MC, you can make pretty sound observations using your own senses via your eyes and nose.

Visual Inspection

Drywall that has been compromised by water can appear to be discolored or show signs of deterioration or crumbling. If you’re able to see such damage with your naked eye, this is a sign that the moisture may have spread farther than the eye can see and the area will require a more in-depth inspection with the use of a moisture meter.

Odor Inspection

If you’re able to smell the musty order of an area suspected of having water damage, then it’s likely there’s, in fact, major water intrusion. If this is the case, then it’s recommended that you find an expert in mold remediation to address the issue.

Mold has likely grown in these areas due to surrounding warm temperatures, tiny mold spores due to unsterile conditions and nearby moisture.

Finding the Right Gypsum Moisture Meter

Acceptable moisture levels vary depending upon the type of material. Therefore, it’s important to use the right moisture meter for your inspection. When testing gypsum board, you’ll want to either use a gypsum moisture meter or use a multi-scale meter that is set to the gypsum scale. Delmhorst’s moisture meter models BD-2100 and TechCheck Plus have scales that are calibrated specifically to gypsum.

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Given the challenging conditions of building inspection, installation and drying jobs, it pays to have an simple, intuitive moisture meter you can depend on such as Delmhorst’s  easy-to-use 2-in-1 TechCheck PLUS, calibrated specifically to gypsum.

For use on drywall, the Delmhorst BD-2100 has a digital display, an adjustable alarm and Delmhorst’s exclusive calibrated drywall scale.

We have found that the equilibrium moisture content (EMC) for gypsum board at 50% RH is 0.3%. Samples exposed to 80-85% RH equalize at 0.4-0.5%. At 90-95%, they equalize at 0.7-0.8% MC.

At these high levels wood equalizes at about 20%, the generally accepted threshold for wood decay. The actual threshold depends on the length of time the high level of moisture has persisted, the source, and even the type of paint or coating.   

So readings of 16+ taken on drywall with the meter set to the wood scale are an indication that the material being measured is at least wet enough to warrant caution and further investigation.

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The readings the meter provides of up to about 1% on the drywall scale (20% wood) are of most value since a tremendous change in conductivity occurs at around 2%. For all practical purposes, readings above this point are compressed and should be considered more qualitative.

For more help finding the right moisture meter for your job, contact our moisture meter specialist’s at  877-DELMHORST (335-6467).

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Topics: moisture meters gypsum wallboard

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