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Mold. It’s ugly. It’s smelly. And it starts to grow long before human senses can detect it. If you can see or smell it, the mold colony is already well-developed and causing harm. The mold can weaken the material causing structural damage. Breathing in the mold spores damages people’s health.

It’s smart to conduct a mold inspection before its presence becomes apparent. Prevention and early detection of mold are critical to mitigating the potential damage. Fortunately, we do know the ideal conditions for mold to grow: dark, moist, and humid. If you can identify those conditions, you can take steps to prevent mold.

Enter the moisture meter. It cannot detect mold. It’s a moisture meter, not a mold meter. Moisture, of course, is a critical condition necessary for mold to fester. A moisture meter can detect moisture content that can’t be seen by the naked eye. By alerting you to the presence of excess moisture, a moisture meter is a vital tool in the anti-mold fight.

For example, wood with a moisture content above 20% is probably holding too much moisture. Different materials, from drywall to concrete, will have different moisture thresholds. A moisture meter that can provide a detailed picture of where a structure is holding too much moisture is a spotlight. It tells you where mold testing or prevention measures should be directed.

Where to Use a Moisture Meter for Mold Detection

Moisture and mold go hand in hand. Mold is a risk anywhere excess moisture can accumulate.

The first places to look are those where moisture, in the form of liquid water, is noticeable. Bathrooms, kitchens, around doors and windows, or a utility room are all places with water. That makes them natural spots for water to pool if it’s not drained.

Then there are the places through which water travels or are conduits to the outside. Wherever a building’s plumbing runs are sites to test. The same is true for gutters and HVAC vents. Gutters that aren’t maintained can trap moisture around the roof. HVAC overflow plans and vents are high risks for mold because they might not only contain moisture but heat as well. Temperature, of course, is another critical condition for mold growth.

Basements and attics are high-risk areas because they’re often dark, closed spaces in contact with outside elements. Rainwater can collect in attic walls or floor due to shoddy or old roofing or cluttered gutters. Basements can absorb moisture from the soil or absorb pooled water, especially where there’s a weak foundation. A foundation that was poured on an improper grade or not given enough time to cure will crack. Moisture seeps into these cracks, making them good mold breeding grounds.

Any basement or attic that’s unfinished is highly susceptible to moisture in the air. Any dark and humid space will absorb moisture in the air into the building materials. Spaces between layers, like wood over a concrete subfloor or wood moldings along a wall, are excellent places for a mold colony.

There are a lot of places where accumulated moisture and humid conditions can lead to mold growth. A thermo-hygrometer, which measures the relative humidity (RH) in the air, is a useful tool to narrow down your focus. Measuring the RH in the air of a room or by a feature can be the first indicator that you should take a closer look.

The EPA recommends an indoor RH level of between 30 and 50% as healthy. If you use a thermo-hygrometer to measure the RH around some open pipes in the basement, a reading above 50% is a flag to go in with the moisture meter. Some of the more sophisticated moisture meters include a thermo-hygrometer.

Moisture Meter Options: Pin and Pinless

Wood moisture meters come in two basic varieties: pin and pinless. The difference is in the technology they use to determine moisture content. These meters measure moisture in wood but often work with other building materials too.

Pin meters: Two pins are inserted into the wood, and an electric current runs between them. Since water conducts electricity, the meter measures the resistance in the current: the more resistance, the less moisture in the wood.

Manufacturers make pins of varying depths. For material that’s thick, you may want to test for moisture at different depths. Unfortunately, switching out pins takes time, which slows the process down. And we all know the more time needed to take a reading, the fewer readings will be made. Thus, varying pin depths is no guarantee that comprehensive moisture measurements will be taken. This is especially true since pin meters can only read the small horizontal area between the pins. Depending on the surface area that needs measuring, you may already need to take numerous measurements at the same depth.

Another challenge with pin meters is that the pins have physical vulnerabilities. The air temperature impact on the pins can interfere with reading accuracy. It takes pressure to insert the pins, especially in dense material. Too much or repeated pressure can strip away their insulation or even break them.

Pinless meters: A pinless moisture meter uses electromagnetic waves, not electric current, to measure moisture. The pinless moisture meter has a large plate that you lay flat on the surface. It emits a signal into the wood or other material. It pushes out a radio signal that returns to the meter. The returning waves diminish in amplitude when they contact moisture. Thus, the meter converts the changes in the waves into a moisture measurement.

The biggest challenge with the pinless meter is that it has to lay flat. A warped or coarse surface may interfere with its readings. However, the pinless moisture meter covers more ground that a pin meter. So for large, flat surfaces, like a floor or wall, a pinless meter is fast, thorough, and accurate.

Another pinless meter benefit is that it’s less affected by the ambient conditions. Best of all, unlike a pin meter, the pinless sort doesn’t create holes in the material.

How to Predict Mold Growth with a Moisture Meter

Taking an accurate moisture reading isn’t difficult if you follow some best practices. This list applies to measuring moisture content in wood.

  • Make sure the meter is calibrated for accurate moisture meter results. Some pinless moisture meters can be re-calibrated on site. Other moisture meters need to be sent to the manufacturer to get re-calibrated.
  • If you’re using a pin meter, inspect the pins for physical integrity as well.
  • Select the pin length or depth setting on a pinless meter based on the thickness of the material. If you can measure the material from both sides, you may not need to alter reading depth to get a full picture of the moisture content. Make sure you insert the pins to their full extent but don’t use so much force you might break the pins.
  • If using a pinless meter, also select the wood species. The wood’s density impacts the wave movement. The meter can account for density in its calculations if it knows what species is being measured.
  • Follow the grain of the wood when placing the pinless meter or inserting the meter’s pins.
  • Know where studs or other metal components are in the area being measured. The pin can’t get through them, and they can interfere with a pinless meter’s readings. Pieces like copper wire or metal pipes won’t interfere with a pinless meter if they’re at least one to 1.5 inches below the surface.
  • Take multiple readings relative to the size of the area you need to assess. Look for a moisture meter that can log measurement data for the most accurate and secure record keeping.

When measuring the moisture content of another material, you want to get a baseline. Starting with a baseline isn’t a bad practice for wood moisture readings, either. At the very least, you should know what the ideal moisture content for wood is in a specific setting. However, you can still get useful moisture reading on wood without a baseline. As noted above, a moisture content above 20% in wood is a mold red flag.

For other materials, like carpeting or drywall, find a spot that you know doesn’t have excess moisture. Put the meter in relative mode and take a reading on the known dry place. A meter in relative mode doesn’t measure the moisture level in the material. It indicates how much more moisture a spot has than the baseline. Some may return a numerical value; others use a color scale to show the degree of variation. You can find pin and pinless meters that have a relative mode.

In all cases, consult the manufacturer guide for your chosen meter. Understanding the functional specifics of your moisture meter will optimize its use to you.

Preventive Measures and Warning Signs of Mold

As noted, mold spores in the air settle in warm, damp places long before they grow into a mold colony. Then that mold colony can grow and fester for a long time before we can detect it with our senses. Even excessive coughing, which can occur in some people who spend a lot of time in a room with mold, means you already have a mold problem.

Even so, there are clues you can see that warrant closer inspection with your moisture meter. If you see any pooled water, that’s a bad sign. Drain or dry the area. Once it’s had a chance to dry, you can inspect it for these signs of excess moisture:

  • water stain
  • rust
  • cracks, especially if there’s staining around them
  • small insects or water bugs congregating in a high-risk area like a bathroom corner or along some molding
  • changes in the wood’s color

Such signs may exist even if you haven’t found standing water first. Taking regular looks around the high-risk areas is an effective way to notice changes.

It’s easy to do regular mold home inspections as part of a moisture prevention plan. Spores can survive cleaning. While that’s a good time to do a visual check, cleaning won’t prevent mold growth due to moisture.

Instead, you want to ensure spaces are well-ventilated. The fresh airflow helps move moisture out. Regularly check that HVAC vents, gutters, and window frames are clean, so the air moves freely. Keep doors open inside the building and run fans to circulate air.

Maintaining a climate-controlled interior will also help prevent mold. Monitoring humidity inside will tell you if it falls outside that 30 to 50% range. If it gets too high, which mold spores will love, you can use a dehumidifier or improve air circulation to bring the humidity down.

A Moisture Meter Is a Powerful Tool in the Fight Against Mold Damage

A capable moisture meter has many roles to play in the fight against mold. It starts, with the help of a thermo-hygrometer and visual inspection of indications of moisture, by finding spots most at risk.

The best-case scenario is that the moisture levels are acceptable. Next, best is that the moisture meter has revealed excess moisture, but mold testing doesn’t indicate any mold. Now the area can be dried out and preventative measures put in place.

If the mold testing does show the presence of mold, then the moisture meter has helped uncover it. Regular moisture meter testing ensures that any existing mold can be caught before it results in severe damage. The sooner mold is discovered, the more effective and less expensive the moisture mold solutions are.

Using a moisture meter to prevent or minimize mold damage requires accuracy. Relying on a lower-grade moisture meter undermines the goal of finding mold-inducing conditions.

The average cost of a mold removal and remediation project for a house is around $2300. However, these costs do not touch on the miserable life quality and potential medical bills for those living in a house with mold. Preventing mold should be the goal. In that endeavor, a moisture meter is indispensable.

If you’re currently in the market for a moisture meter, don’t buy one until you check out our reviews (including both pros and cons) of 9 top tested meters.