How to Use a Wood Moisture Meter for Drywall
What Is Drywall?
Drywall is a popular material used to create walls and ceilings, for both homes and offices. During the mid 20th century it started replacing the old lath and plaster technique because it was inexpensive and easy to install. If you live in a home built within the last 60 years or so, you almost certainly live in a home with drywall.
Drywall’s main ingredient is gypsum, a non-toxic mineral that’s mined in countries around the world. Drywall is created by grinding the gypsum crystals to a powder, mixing it with water, and then surrounding it with paper to create the familiar drywall panels. In other words, a panel of drywall is basically just a gypsum core surrounded by paper.
Drywall was invented in the 19th century (patented in 1894) by Augustine Sacket as a labor-saving device because it was easier to use than plaster. The US Gypsum Company (USG) later bought the invention and today it’s the world’s leading manufacturer of drywall. Drywall really took off in the 1950s with the post-war building boom and today it’s used in almost all new homes.
There are different types of drywall. Greenboard is moisture-resistant drywall created by surrounding the gypsum core with a moisture-resistant covering. You can also buy fire-resistant drywall and drywall that’s flexible enough to create curved walls or ceilings.
Why It’s Important to Know If There’s Moisture in Your Drywall
Drywall and moisture don’t get along. This is because drywall is very porous and easily absorbs and holds moisture. Even a small amount of excess moisture is too much for drywall. If you have excess moisture you’ll need to either dry it out somehow or remove and replace it.
If you splash a bit of water on drywall and then wipe it off right away you should be OK. If it’s a larger amount of water you can dry it off with a towel and then turn a fan on it until it dries. However, if drywall comes into contact with moisture over a longer period of time it can be damaged beyond repair. Even if you could dry it out, it wouldn’t look the same because it will have lost its shape, and if pressure is applied, it will crumble. Drywall is not load-bearing, so it won’t affect the building’s structural integrity but it will need to be replaced at this point.
Mold is also a problem because it doesn’t take much to get it growing in drywall. If you smell mold in your drywall, you should replace the affected panels right away.
Although greenboard is more moisture-resistant, it’s not impervious to moisture. If moisture makes it past the covering, you’ll have the same trouble with greenboard as you will with regular drywall.
Because drywall is so sensitive to even small amounts of moisture it’s important to measure its moisture content. You need to know where these minute amounts of moisture are, and if you find any, you need to be able to monitor the drying process to make sure that all excess moisture has been removed from the drywall.
Not All Moisture Meters Have a Relative Mode
While it’s important to use a moisture meter on drywall, not all moisture meters have a relative mode. Using a relative scale may be the easiest way to test. Having a meter read something that is not the correct moisture content for the drywall may be confusing. However, a relative mode may help the user remember the goal is to find the wettest areas. These wetter areas are where you need to focus to make sure that the drywall is dried out or replaced. Also, using a moisture meter can help a person trace down areas where water may be entering the structure.
How to Use a Wagner Moisture Meter for Drywall
The first thing you need to do is find out where the moisture in the drywall is located. Sometimes, there will be visible signs of moisture. These include discolored areas, a musty odor, or drywall that’s starting to crumble. These signs all indicate that there’s significant water damage to the drywall.
Once you think you know where the moisture-damaged areas are, you’re ready to take your first moisture reading:
- Put your Orion® moisture meter in Relative Measurement mode. You can do this by pressing and releasing the SPECIES/MATERIAL button until you see REL on the main LCD display and also in the lower-left corner. Next press the ON/HOLD button to activate the mode. Once you’re in this mode, your meter will be on a relative measurement scale (0-100). This is used for measuring non-solid wood or non-wood based materials, including drywall. (When you want to return to the Standard Measurement mode, press the SPECIES/MATERIAL button.)
- Find a known dry spot and take a reading. The other readings you take will now be compared to this one.
- Scan the wall to find spots with a higher moisture content than the known dry spot. These will be the areas of the drywall with a moisture problem.
The Orion series of pinless moisture meters’ Relative Measurement mode make it the perfect choice for anyone — building inspector, homeowner, or otherwise — who wants to measure the relative moisture content of drywall. Read more about Wagner’s Orion series of pinless moisture meters.
Tony Morgan is a senior technician for Wagner Meters, where he serves on a team for product testing, development, and also customer service and training for moisture measurement products. Along with 19 years field experience for a number of electronics companies, Tony holds a B.A. in Management and his AAS in Electronics Technology.