How a Moisture Meter Can Help Find Moisture and Mold Growth
Mold can grow almost anywhere in a home that stays damp, and it can damage building materials and affect the people living there. Moisture meters can’t detect mold itself, but they can find the damp conditions mold needs to grow.
This guide explains the warning signs of mold, where the moisture behind it comes from, and how a moisture meter helps you catch moisture problems before mold takes hold.
- Can a Moisture Meter Detect Mold?
- What Are the Warning Signs of Mold?
- The Icky-ness of Mold
- How Mold Happens
- What Causes Moisture in Walls?
- How to Eliminate Mold?
- Is There a Moisture Meter for Mold?
Can a Moisture Meter Detect Mold?
No, a moisture meter can’t detect mold, but it can find damp areas where mold might grow. With a pinless moisture meter, you can scan the surface of wood, drywall, and other materials to find areas with too much moisture.
Moisture meters help you find damp spots where mold could grow. Wood that stays below about 20% moisture content (MC) generally won’t support mold, so if a reading in wood is above 20%, check the area for mold and find the source of the moisture.
Humans have reason to attach negative connotations to mold. When food goes bad, mold appears. When a living space holds too much unventilated moisture, mold grows. Fabric stored in damp places gets its musty smell from mold.
More seriously, mold releases spores and other substances into the air as it grows inside a home, and over time this can affect people’s health. As the U.S. Environmental Protection Agency puts it, “The key to mold control is moisture control.”
What Are the Warning Signs of Mold?
Discoloration and the Bleach Test
Discoloration is one of the most apparent signs of a mold issue. Mold can appear in various colors, including black, green, white, orange, and even pink, depending on the type and the surface it grows on.
For a quick home check, dab a little diluted household bleach on a suspected mold spot. If the stain lightens or disappears, it could be mold. However, some stains and some types of mold won’t react to bleach, so it’s not a definitive test. Wear gloves, keep the area ventilated, and never mix bleach with ammonia or other cleaners.
Musty/earthy smell
Mold has a distinctive, earthy smell often described as musty. If you detect an unusual persistent odor, it may indicate hidden mold. Such an odor can come from behind wallpaper, under floorboards, inside walls, and other areas where mold commonly grows.
Water stains or dampness
Mold loves moisture. Any signs of dampness, such as water stains, peeling paint, or warped walls and floors, may indicate a moisture problem and potential mold growth. If you notice any such signs, it’s important to identify and fix the water source as quickly as possible to prevent further mold growth.
Condensation on Surfaces
Mold grows readily in humid environments. Regular condensation on windows, pipes, or walls may suggest higher-than-normal indoor humidity and the potential for mold growth. The EPA recommends keeping indoor relative humidity below 60%, ideally between 30% and 50%.
Visible Growth
In advanced stages, you may see visible mold growth. It can appear as a fuzzy, slimy, or powdery substance and may have a green, black, white, or brown color.
The Icky-ness of Mold
Here are some more basic points on understanding mold:
- Mold needs moisture to grow.
- Dampness inside building materials can cause mold to grow.
- Mold will not grow on dry materials.
- Mold can start growing in places where no water can be seen.
How Mold Happens
Moisture is present in every building because it is part of our natural environment. Builders construct homes using wood and concrete (among other materials), and both contain some moisture.
Professional installers use a moisture meter to measure the MC of their materials during the building process to make sure they’re at safe moisture levels.
Today, moisture meters are easy enough to use that homeowners as well as contractors can check building materials regularly to see if their MC changes.
What Causes Moisture in Walls?
Moisture can move up through concrete floors, leak from plumbing, roofs, and windows, and come from everyday activities like bathing, washing, and cooking. Moisture naturally builds up in homes, and the excess needs to be ventilated.
Even changes in relative humidity (RH) can influence the MC of building materials. When RH is high, materials such as wood absorb water vapor from the air; when RH is low, the same material releases water vapor as it moves toward a balance with the air.
Building materials constantly interact with the RH and temperature of their surroundings. That’s normal, and not something to fear.
It becomes a problem when too much moisture builds up in one area without ventilation, which can lead to mold growth.
If you want more information on how to use a moisture meter on drywall, read our comprehensive guide.
Free Download – Is a Pin or Pinless Moisture Meter Best For You?
How to Eliminate Mold?
You can’t eliminate moisture entirely, but you can eliminate the moisture problems that lead to mold. Find and fix the source of the water, and dry water-damaged areas and items within 24 to 48 hours to prevent mold growth, as the EPA advises. According to the EPA, if the moldy area is smaller than about 10 square feet, you can usually clean it up yourself; larger areas call for professional help.
Building professionals use moisture meters to measure the MC of wood building materials and RH tests to measure the moisture in concrete slabs. Both readings are shown as percentages, and quality builders know the moisture targets for their materials. In essence, they have the tools to stop mold before it starts.
Professionals monitor moisture conditions through the production and installation of their wood building materials and during the curing of concrete slabs in order to make the best construction decisions for a successful project.
Is There a Moisture Meter for Mold?
There’s no moisture meter that detects mold itself, but Wagner Meters makes moisture meters and moisture tests for wood, concrete, and other building materials. Wagner Meters’ handheld wood and building inspection moisture meters quickly scan materials to give instant MC readings.
Homeowners can buy their own meter to check for moisture problems in their homes and fix them before they lead to mold.
Moisture will always be with us, but excess moisture doesn’t have to lead to mold in the modern home. Use a good moisture meter and keep moisture at appropriate levels so mold doesn’t get the chance to grow.
For woodworkers, controlling wood moisture content matters just as much. Read our article “Controlling Wood Moisture Content: A Key Factor in Woodworking Success” to learn more.
As Sales Manager for Wagner Meters, Ron has more than 35 years of experience with instrumentation and measurement systems in different industries. In previous positions, he has served as Regional Sales Manager, Product and Projects Manager, and Sales Manager for manufacturers involved in measurement instrumentation.
Last updated on October 7th, 2026
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I’ve had an issue with underground pipe leaks. The first indication was that my cold water came out boiling hot and took up to a minute to get cold. A plumbing company out and said a leak in the hot water pipe was causing it. I live in a condo (just under 700 sq feet). The leak ended up being in a unit in the building behind me. But when they pulled up my water proof laminate flooring to get access, the flooring came up dripping, sopping wet due to cracks in the concrete. My floors were also warm along the whole kitchen and vanity area of my condo. This issue had been going on for months. It also turned out there were cracks in my cement in my entire condo. Restoration company came out with dehumidifiers and dried everything sufficiently to lay new flooring. According to their report, they metered along the bottom of the walls, but no mold inspection was done. My first thought is that it should have been at the top of their list. I also discovered that part of their service is mold inspections and remediation. Was a mold inspection called for?
Hi Gloria,
This is really out of our wheelhouse. I would highly suggest contacting NORMI, https://www.normi.org
I’ve been trying to figure that out too. One website says 20%, still looking around for other websites to confirm
This is a very helpful article. We have found that mold damage is usually the result of hidden moisture. As a mold water damage specialist in South Florida, we often find roof damage is the most common. Once a homes roof is compromising the rain water, soaks into the insulation where is may sit for weeks or even months. It only takes 24-48 hours for mold to start growing. Once that happens your homes walls or ceiling will need to be replaced. My advise is the homeowner need to form the habit of searching for water spots on walls and ceilings on a regular basis.
Can a mold meter detect mold under ceramic tiles in the bathroom?
Zeenat,
You will need to check with the manufacture of the meter to determine its use. Thanks for writing in.
Is there a % on my moisture meter that is when mold will grow inside a wall
Hi Lynn,
Thank you for writing in. Moisture meters do not have a percentage that will show mold. That said, I would go to NWFA.org. They have wonderful information on their site.