How To Use A Moisture Meter On Drywall & Wood (My 6 Step Guide)

Are you interested in learning how to use a moisture meter on drywall or wood to detect their water content?

As a home inspector, my moisture meter is a top tool I use for finding leaks and probing problem areas (here is what I think is the best moisture meter).

In this guide, you will learn...

  • How to use a moisture meter
  • Knowing about false signals
  • What materials will not work with moisture meters
  • And more...

Let's get started with this guide!

how to use a moisture meter

Introduction

A moisture meter is an incredible tool to use to check the moisture content of various materials. Home inspectors frequently use moisture meters to check water stains, drywall patches, and problematic basements for water intrusion. The EPA even has a guide on using a moisture meter to check firewood.

Flooring professionals sometimes use moisture meters to check the moisture content of wood subflooring (before laying out new flooring). There are many other reasons as to why someone may want to purchase a moisture meter.

Here are my detailed steps on how to use a moisture meter on drywall and wood...

#1. Turn On The Moisture Meter

Most moisture meters will require a few AAA or AA batteries. Make sure good batteries are installed, and that the batteries are in the right direction.

Press and hold the power button to turn on the moisture meter.

#2. Select The Correct Mode

Moisture meters come with various modes for testing different types of material. The most common settings are for softwood, hardwood, masonry, and drywall. By far, the most common setting during my home inspections are drywall.

Simply select the arrow button or mode button until you are on the right material setting.

#3. Understanding The Signal Outputs

Many moisture testers will have 3 outputs on the screen such as percentage, sound, and a color scale.

For example, if you put the meter on a moisture stain on the ceiling, and if it has alot of moisture, then you may get a percentage reading of 90%, you will hear a loud audible beeping, and you may get a red color.

If the moisture content is very low, then you will get a reading of 5%, you will NOT hear an audible beep, and the color will be green or yellow.

how to use a moisture meter

#4. Select Either The Pin Or Pinless Sensor

Many of the best drywall moisture meters have to moisture sensors that you can use. The pin sensor consists of two metal pins that you can insert into softer materials such as carpet.

As a home inspector, I frequently find that the corners of basements have water problems (usually due to poor exterior grading). Well, having a pin sensor is great because I can probe the corner carpet to see how wet the floor is. A pad sensor will not give me an accurate reading.

However, if you want to test a hard or flat surface such as drywall or wood paneling, the you definitely want to use the pad (flat) sensor. You don't want do damage the wall or ceiling material.

With the flat pad sensor, you can sweep large areas very quickly checking for moisture.

Read Also: Why Polybutylene Piping Cause Water Leaks

#5. Beware Of False Signals

Now it's time to actually use the moisture meter. But before you do, it's important to realize that there are some limitations and false signals with moisture meters.

Metal Corner Beads

In my experience as a home inspector, one of the most common false signals with these meters are with metal. Especially with drywall or gypsum walls, there are almost always metal strips at the corners of walls and windows where a metal "corner bead" was installed.  Sometimes instead of metal, drywall installers use vinyl corner beads, but I think it is pretty rare.

Frequently when I am checking a basement window, I am very conscious that the metal strips will cause a false reading, and the moisture meter will usually go to 100%.

If at anytime you are in a drywall corner area or within a few inches, and you get a reading of 100%, there is a good chance that it is a false signal.

Significant Moisture Readings

Besides the metal corner beads, it's also important to realize that not all moisture readings are equal. In my experience, if the moisture meter signals 5% to 10% moisture, this barely even registers to my brain.

I am always looking for more substantial readings, more like in the 60% to 90% range.

Concrete Or Masonry Block

Many moisture detectors have a "masonry" mode to detect moisture in concrete or block, but in my experience as a home inspector, I have found that it isn't reliable whatsoever.

Concrete and cinder blocks naturally "breath" and are not water tight. Moisture is constantly going in and out of concrete because it is a porous material. I have never put a moisture meter on a foundation wall and not received a very high moisture reading. If I found this significant, then I would be worried about every foundation I ever inspected. I do not take these readings seriously.

Read Also: Tips & Traps When Buying A Home

#6. Where Can I Use A Drywall Moisture Meter?

As an inspector, the absolute most common areas I use my sheetrock moisture meter on gypsum walls, drywall ceilings, and wood paneling --- that's pretty much it.

Stains And Drywall Patches

I walk through the house with a high powered flashlight, and any time I see what looks like a moisture stain, I pull out my moisture tester and check to see if the stain is active. If the moisture meter has a reading of 20% or more than the surrounding area, then I know there is still some kind of leak (or condensation problem) going on at this spot.

In addition to moisture stains, I also always check drywall patches. There is a reason that someone did a repair, and quite often it has to do with a plumbing leak, especially if it is the ceiling.

Construction Materials

Before installing framing, wood floors, or other materials, it can be a good idea to check their moisture content especially if they have been outside or in the rain. 

You may want to wait until the material dries out and drops below a certain moisture level before the installation.

If the moisture content of wood material is excessive prior to installation, it can cause the wood to warp and bow after it has been installed.

Be careful with wood however because the readings may vary with wood species, temperature, and chemical treatments.

Basements

Home inspectors frequently find water problems in basements, it's almost a cliche. The usual reason that basements have water issues is that the exterior grading is very poor. The ground should slope away from the home, but frequently it is flat or even sloping towards the home.

Related to exterior grading, I frequently inspect homes that have missing downspout extensions or even missing elbows. The roof discharges large amounts of water during rainstorms, and if your downspouts are spewing water by the corner of the home, water can easily intrude into the basement (especially the corners).

Many times when I am doing a home inspection, even I don't suspect water issues, I still quickly take a few moisture readings of the corners and a few other areas below grade.

Behind Decks

Many times I find water problems in the basement or ground level of a home where a deck is connected.

The deck is connected to a home by using lag bolts that are screwed into a piece of wood called a ledger board.

Before the deck is connected, the contractor is supposed to install metal or plastic flashing to prevent water intruding in the home during rain storms. In my experience as a home inspector, I find that 90% are not properly flashed.

This is why I always check underneath the deck (inside the home) at the interior wall. If I am getting moisture readings inside the home under the deck, then I know that the deck is not properly flashed and is leading to water problems --- and may lead to mold problems.

Conclusion

There are many benefits of using a moisture detector as a homeowner or a professional. It can be very difficult to determine leaks in a home that aren't visible to the naked eye. 

Even though I can sometimes smell water issues in a basement --- it is very distinctive --- it is still important to confirm this suspicion and also to determine where the water is coming from.

Using a moisture meter is pretty simple, just make sure it is in the correct mode, avoid false signals, and know where to use it.

I hope you enjoyed my guide on how to use a meter. If you have a question or would like to share an experience with drywall moisture meters, then leave a comment below.

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company (read his full bio on the About page). To ask Arie a question, please use the comment box at the bottom of the relevant article.

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