A moisture meter is a device designed to measure the percent of moisture content of various building materials, such as roofing, siding, insulation, drywall, plaster, wood, tile, fiberglass and concrete. Structural and safety hazards, such as mold, rot and decay are all potential consequences of elevated moisture levels in these materials.
All homeowners should own a quality moisture meter since they can easily use it to locate moisture that would not otherwise be apparent. In addition to that if the homeowner does have a leak he or she can use the moisture meter to determine just how much surrounding building material become wet.
Keeping your home dry especially after a leak is one of the key way to prevent mold. Mold will begin to accumulate on surfaces that contain approximately 20% moisture, although this value varies based on vapor pressure and other factors. A moisture meter can be used to determine whether a material is moist enough to allow mold to grow.
Aside from helping to find leaks and check the moisture content of building materials that are known to be wet, a moisture meter can assist a homeowner in determining whether wood is dry enough to be painted or stained. You NEVER want to seal moisture in to wood.
If you are installing anything in your home that is made of wood (cabinets, lumber, wood flooring, etc…) you can use moisture meters to make sure that the wood is dry enough to be installed. Installing already damp wood in your home is an open invitation for mold growth.
Moisture Meters – The Basics
Moisture meters come in three different varieties known as pin type, pinless (also known as search mode) and all-in-one. They are each suited to different applications which I will discuss further.
Pin Type Moisture Meter
This moisture meter type is used to measure the moisture content of a material’s surface, or at an incremental depth using probes. While in this mode, the meter can measure the amount of moisture on a material by its electrical conductivity. This is often regarded as a more repeatable and accurate type of moisture measurement than the “search mode” described below, although intermittent wet spots in the wood may be missed by pin type meters.
This method can be used to test for moisture on the surface of building materials, such as stucco, drywall, plaster or wood. It is especially useful for determining if the source of a stain on a wall or ceiling is from an active leak.
Probes of varying lengths and designs may be used to extend the reach of a moisture meter operating in this mode. They are slender metallic poles with sensitive tips that extend the reach of the meter’s electrodes. Delmhorst makes probes that can be inserted deep into the straw in straw homes to measure its moisture content. Hammer probes can be driven into wood and then extracted. Other probes can be inserted into pre-drilled holes in masonry, or pushed through insulation. Moisture content in log homes can be measured by inserting a probe two-thirds of the way from the log’s surface to its center.
Search Mode – AKA Pinless Moisture Meter
Search mode, also known as pinless mode, detects and measures moisture content beneath the surface of a material. Meters in this mode emit electromagnetic waves (usually radio waves or an electrical current) that are affected by the presence of moisture. The meter can detect changes in the characteristics of returned emissions and then use this information to calculate moisture content.
Some pinless moisture meters operate by the principle that a material’s impedance (resistance) to an electrical current varies inversely with that material’s moisture content. This moisture meter determines the amplitude of a low-frequency alternating current, and uses this information to calculate moisture content.
Other pinless moisture meters detect the characteristics of emitted radio waves in order to determine the presence of excess moisture. These meters detect the amplitude of returning waves, which is diminished when they come in contact with water.
The actual depth that these waves travel varies based on the material’s properties and the device’s settings, but they generally penetrate from ½” to ¾” beneath the surface and are unaffected by surface moisture. Unlike the pin type, this mode of operation arrives at a relative value for moisture content that must be calibrated, using an external equivalency table in some models.
The pinless moisture meter will display moisture content as a scale of color-coded lights that indicate whether the material is damp, dry, or in a borderline condition. In some models the default setting can be used to approximate moisture content in most materials, although dense materials, such as cement, will require adjustment of the device’s controls. In addition, some pinless moisture meters take a three-dimensional moisture average of the wood, which decreases the likelihood that intermittent wet spots will be missed.
A pinless moisture meter is commonly used in the following locations:
- The sides and the base of a tub or shower. Any penetrations, such as faucets, showerheads and soap dishes, are likely locations of water leaks. The water can originate from internal plumbing behind the wall, or from the shower itself.
- Water that has escaped from a dishwasher into surrounding kitchen materials.
- The sub-floor beneath a bathroom’s tile floor. Water intrusion can cause enough damage there that the toilet becomes detached.
- Peering behind a wall or floor covering, such as a vinyl floor or a tile wall.
False Readings With A Pinless Moisture Meter
If metal is present within the penetrating range of the meter, it will alter wave characteristics in ways similar to water. The meter will report levels of moisture that are higher than the actual level of the material if it detects a copper wire, a metal pipe, or some other metallic substance.
This is where using a pinless moisture meter can get tricky for the average homeowner. If a mold inspector suspects that the meter is sensing metal, s/he can monitor the readings as s/he moves the meter in a straight line away from the elevated reading area. The straight outline of a copper wire or metal pipe can usually be traced in this fashion.
A homeowner certainly can attempt to figure out whether or not there is metal giving out false moisture reading but using a pin-type moisture meter in conjunction with the pinless moisture meter. In fact, these types of moisture meters are my top choices since they give you the best of both worlds. Using a thermal imaging / infrared camera can also help you confirm or deny a leak or other water intrusion. If you are unsure, always consult with a professional mold inspector.
Pin/Pinless/All-in-One Moisture Meter
A third and possibly more useful moisture meter would be a pin/pinless/all-in-one moisture meter. This type of moisture meter utilizes both methods for measuring % of moisture content in surfaces. Because this type of meter offers the option to measure moisture content in substrates using both methods of reading moisture, one meter may be able to identify problem areas and then also be used to pinpoint the exact location where moisture damage or buildup is occurring.
Essentially, this type of meter would utilize the same scales of moisture content for wood and nonwood substrates and allow the homeowner the versatility necessary for a full inspection in determining areas where moisture is an issue.
How To Use A Pin-Type Moisture Meter
- Turn on the moisture meter
- Select the mode and/or material
- Push the pins into the surface at a perpendicular angle and take the reading
- Remove the moisture meter
How To Use A Pinless Moisture Meter
- Turn on the moisture meter.
- Place the sensors on top of the material to get a reading
Establishing A Baseline Reading
A lot of variables can come into play when using a moisture meter. This is why it is important to establish a baseline reading.
A baseline reading is a moisture content measurement that the homeowner takes in an area that they know is not impacted by a leak or other water intrusion. Ideally this should be taken in the same room as the other moisture measurements.
A baseline reading establishes normal moisture content for the building material in that room. Anytime you find readings that are higher than the baseline, you know there is more moisture in that particular area.
Having said that, if you are attempting to get a baseline reading but the entire room is showing elevated moisture then likely there is a significant issue in that room.
Do Moisture Meters Detect Mold?
Even the best moisture detector doesn’t have a “mold” setting, but it can identify pockets of moisture that may contain mold spores or have active growth occurring.
Can I Use A Moisture Meter Both Inside And Outside?
Most moisture meters work within a designated temperature range, such as between 32 degrees and 104 degrees Fahrenheit. You can use them both indoors and out provided you stay within the temperature rating provided by the manufacturer.
Like I mentioned previously, every homeowner should have a moisture meter handy. I use mine often as part of my mold prevention and leak detection strategy.
Let’s take a look at my recommendations for pinless moisture meters, pin-type moisture meters, and combination moisture meters. The top 7 moisture meters really are the best in the business and the ones that professional mold inspectors use. Most of them are really affordable for the average homeowner and no matter the cost, can potentially save you tens of thousands of dollars from a leak that was left undetected for too long.
The Top 7 Moisture Meters For Drywall, Concrete, Wood and Other Building Materials
#7 Ryobi E49MM01 Pinless Moisture Meter
One of the most popular moisture meters, the Ryobi Pinless Moisture Meter detects moisture ranges of 5-30% in hardwood, softwood, drywall, and masonry.
- Audible alerts change in frequency as you run into higher levels of moisture
- Easy to read – the LCD screen shows, in large numbers, the percentage of moisture
- Even without pins, this tool can read the moisture levels up to a half inch deep into your surface of choice making it as effective as a pin-type moisture meter
- Extremely accurate
- No backlit display
#6 General Tools MMH800 4-In-1 Combo Inspector Moisture Meter
The General Tools MMH800 4-in-1 Pin/Pad RH Moisture Meter is ideal for locating water leaks and measuring moisture content of wood, drywall, plaster walls, carpeting, flooring, brick, grout, soil, paper or powders.
This tool features both pin-type and pinless surface sensors. With the General Tools MMH800 combo moisture meter, scanning large areas of drywall and wood is easy with the pinless pad sensor. Once moisture patches are detected, flip open the cap to expose the pin sensors for more exact moisture content readings.
It features two displays; one for moisture content and one for ambient temperature and humidity. The unit provides a moisture level range of 5-percent to 50-percent in wood and 1.5-percent to 33-percent in building materials and offers an audible indication of moisture level and storage of moisture level readings. It holds moisture level readings for convenient viewing later. The tool also has an auto diagnostic check and auto power off. Powered by a 9 volt battery (included). The unit also comes with a lanyard, 2 sets of spare pins and a user’s manual.
- Pin-type and Pinless capabilities
- Measures ten types of building materials
- Temporarily stores data
- Delivers temperature and humidity readings
- Audible alarm if moisture is detected
- Affordable price
- This meter can be unreliable. You can trust it to tell you if something is generally “wet” or “dry,” but you shouldn’t take the percentage readings you get too seriously.
- Only a one year parts warranty
#5 Dr. Meter MD-918 Moisture Meter
Dr. Meter MD-918 Moisture Meter For Wood Products is a great choice for people looking only to test wood and drywall. This is a pinless moisture meter and is highly accurate. Dr. Meter MD918 Wood moisture meter has a wide measurement range 4~80%RH with accuracy 0.5%.
- Highly accurate
- Ultra large LCD screen
- Low voltage prompt will auto shut off within 5 mins if no use
- One of the most affordable moisture meters on the market
- 30-Day Money Back Guarantee, 12-Month Replacement Warranty and Lifetime Support Guarantee
- Only good for testing wood and drywall
- Frustrating to calibrate initially
- Even with the large screen it can be tough to read in certain lighting
#4 General Tools MMD950 Moisture Meter
The General Tools MMD950 Moisture Meter is a pin and pinless deep sensing moisture meter which gives you the option of using pins in direct contact with a surface or using a spherical pinless sensor for a more versatile means of measuring.
The meter specializes in detecting moisture content under tiling and in subfloors underneath carpeting and wood flooring. It can also detect moisture in masonry work.
The spherical pinless sensor can measure average moisture levels at up to 4-inches in depth with hardly any contact made. Meanwhile, the pins are connected to a 46-inch cable to allow for measurements in hard to reach areas without having to reach or strain while getting your readings.
- Dual pin and pinless spherical sensor operation capabilities
- Displays percent moisture content or relative readings simultaneously on two displays one a jumbo LCD and the other a 40-dot tri-color LDE bar graph
- Able to detect average moisture levels up to 4-inches deep
- Auto-calibrating digital unit with large LCD display and tri-color bar graph
- Data hold function
- Low battery warning
- A little more expensive
#3 Calculated Industries 7445 AccuMaster Duo Pro Pin & Pinless Moisture Meter
The Calculated Industries 7445 AccuMASTER Duo Pro Pin & Pinless Moisture Meter is ideal for helping you measure moisture content in hardwood, lumber, wood flooring, brick, concrete, drywall and plaster. Its dual-sensor system can help you speed up and improve your moisture detection using either its pad or pins. It’s the best of both worlds.
Measuring Range: Pin mode – 5% – 50% (wood); 1% – 33% (other building materials); Pinless mode – 0.1 – 100% for all materials.
Accuracy: +/- 3%
- Easily fits in hands and lightweight
- Well designed and easy to read LCD display
- Three minute auto off feature
- Hold function allows you to freeze reading
- Icons and audible alerts
- Pin-type and Pinless options
- One year warranty
- Pins are known to break easily in hardwood
- Pins are super sharp to the touch
#2 Sam-Pro Tools Dual Moisture Meter
The Sam-Pro Tools Dual Moisture Meter is a good choice for people who need a massive measurement range. It can measure between 0% and 70% moisture, which is huge relative to other moisture meters.
The Sam-Pro Tools Dual Moisture Meter can also measure the moisture content of just about any kind of wood, fiber boards, particle boards, and even concrete. That makes it one of the most versatile moisture meters on the market, and one that’s great if you’re constantly testing different kinds of materials. It also measures temperature, which is good for a lot of tasks that involve drying.
- Backlit LCD Screen
- Pin-type and Pinless capabilities
- Measures four building material types (hardwood, softwood, drywall, and concrete)
- Wide measurement range
- Easy to use and select building material type
- Large screen with easy to read display
- Most versatile moisture meter for the price
- Come with replacement probes
- Lifetime warranty
- Variable accuracy across its range, varying ±1% under 30%, which scales up to ±3% at 60%-70%. That’s not the most accurate meter on the market, but it’s the most accurate where it needs to be the most accurate, and that’s at the lower range.
- Annoying safety cap that keeps the probes safe.
#1 Protimeter BLD5365 Surveymaster Dual-Function Moisture Meter
The Protimeter Surveymaster is a dual-function moisture meter that offers homeowners a quick, easy, and one-handed way to measure moisture.
The Protimeter Surveymaster has two modes of operation: Search (non-invasive) and Measure (pin-type). These functions allow the homeowner to distinguish sub-surface and surface moisture, which is essential when investigating the extent of a moisture problem.
This moisture meter offers a reference mode. Reference mode can be used in both search and measure modes. Reference mode is helpful when trying to establish what materials are above or below a point of reference or dry standard.
- 70 to 999 relative (pinless)
- 7.9% to 99% WME (pin measurement)
Depth of moisture reading
- Pinless: up to 3/4 in (19 mm)
- Pin measurement: up to 1/2 in (12.7 mm)
- Two modes of operation: search and measure
- Has a large backlit display unit to showcase the readings
- Delivers pin moisture measurements which are very accurate
- Non-invasive measurement which reaches 20 mm below the surface
- One-handed operation simplifies your operations
- Contains improved parts and features
- Rugged and durable
- Includes deep wall probes and spare pins
- Includes a hammer electrode for wood floor applications
- Works well with a wide range of accessories and plugins for more complicated searches
- 2 year warranty
- Expensive compared to other moisture meters
- Adjusting for species and temperature requires using tables
- Requires a bit of specialized maintenance
Part of this article are used with permission from the NACHI article “Moisture Meters For Inspectors.”