Namba's World


Moisture, as we are too well aware, is a major concern to all of the floor covering trades, yet how many installers, retailers or general contractors actually conduct moisture tests on every concrete slab for direct adhered products, or what about wood sub-floors and wood installations? The floor covering industry keeps stating that it is not the responsibility of the installer to conduct the moisture test over a concrete substrate, but if one is not conducted and we install the floor covering and it fails we are responsible; sounds like a double-edged sword to me! For a concrete substrate, calcium chloride testing is still considered to be the quantitative test that will hold up in a court of law, but there are products on the market that will give qualitative results on concrete and industry accepted accuracy on wood with immediate results. Moisture meters have been in the market place for years but are they properly used? In this article we will explain the basics of moisture meters.

Conductance (resistance) pin type meters used primarily for wood, utilize electrodes (pins), of varying lengths from 3/8-inch to 3 inches.

These pins are pressed or driven into the wood and measure the resistance to the flow of direct current or low frequency alternating current, so what does this mean in terms we can understand? When the pins are driven into the wood there is a current running between the two pins, this resistance or conductance is measured and converted to a moisture content reading (MC), water is a conductor of electricity, more moisture equals higher conductance.

With the Conductance wood meters, there are two types of pins, insulated and non-insulated. Insulated pins have a non-conducting coating except at the tips of the pins; this is more common with the one to three inch pins. These longer pins are generally on a slide hammer or something similar, so that they can be driven into the wood material, and attached to the meter via an external connection (Photo 2). Un-insulated pins do not have a coating along the length of the pins therefore; the reading will register at the point where the presence of moisture is the highest between the pins.

Pins that are affixed to a meter are usually non-insulated and are 3/8-inch to 1/2-inch (Photo 1, two outside meters), and can only read to the depth that the pins are inserted. So why the difference between insulated versus non-insulated?

Insulated pins, reading only at the tip of the pins, have the ability to measure gradient moisture content, as the pins are driven into the wood surface, readings can be taken at different depths to determine what the moisture content is at that particular depth.

An example, insulated pins can be used in situations where a reading needs to be taken on the sub-floor where hardwood flooring has been installed that may have had moisture intrusion, but other influences such as adhesive can skew the numbers.

When using pin type meters insert pins running parallel with the grain unless the manufacturer of the meter recommends otherwise (Photo 2).

Conductance meters read between the pins only and are sensitive to the temperature and species of the wood so make sure to refer to manufacturers manual or the manufacturer of the meter to determine the temperature and species adjustments.

Dielectric wood meter, (pictured in Photo 1 in the middle). This type of meter is a non-intrusive meter which means, it does not penetrate the surface of the material being tested. These types of meters are also referred to as capacitance meters. Readings are obtained by firmly placing the meter, which has a platen on the underside, in full contact with the substrate. This type of meter takes an average reading of everything within the sensing area and depth penetration. Results are displayed immediately and several readings can be taken in a very short time, as it is a non-intrusive test.

Depth of reading can vary with manufacturers, this particular meter that was used reads at a depth of 3/4-inch (Photo 3).

Dielectric meters generate an electric field much like radio waves; in fact the results are based on radio frequency (RF). Where there is a presence of moisture, the electric field weakens, how much the electric field weakens depends on a property of the material called the dielectric constant. The higher the dielectric constant (Moisture) the more the electric field weakens, and the meter will register this as a higher number. Dielectric meters must also be calibrated for different species of wood due to the specific gravity of each species. Specific gravity is a measurement to determine the wood's density; the higher the specific gravity, the more dense the wood is. Make sure you check with the manufacturer of the meter to determine if their meters can be field calibrated for the different species. Also, keep in mind when checking moisture for a wood installation that you need to calibrate each species for the area being tested, the floor joists, sub-floor (Photos 4-5 are displaying a plywood sub-floor and OSB sub-floor), and the product that is installed or being installed, as each will have a different setting. The numbers that you read all need to be within a combined 4 percent of each other.

For engineered wood products (Photo 6), contact the manufacturer to get the recommended setting, as these types of tests are more of a relative measurement rather than a semi-quantitative measurement, this is due to the glue and resins that are present in engineered products.

Concrete meters (Photo 6) - Years ago resistance type tests were done by nailing two concrete nails into the concrete surface and then placing two wire terminals connected to a meter, many of these types of meters are still being used today but in a different form. Spring loaded moisture meters are considered Power loss meters and react to resistance of the material.

These are non-intrusive meters so placing nails in the concrete is not necessary (Photo 7, left side). The meter is pressed onto the concrete until the springs are fully compressed then a reading is registered.

Dielectric meters for concrete use the relative density or specific gravity of the concrete to determine a value and use a platen (Plate) placed firmly on the concrete surface, to register a reading (Photo 7, right side).

Concrete moisture meters DO NOT give a quantitative value such as the calcium chloride test. The numbers displayed on the meters are relative, meaning that it is displaying a number only, although most manufacturers recommend a not to exceed value with their meters. One can get a relative reading by taking several readings in an area to get a general idea to determine the variance in the readings. Each manufacturer uses their own set of numbers displayed on their meters, so a reading from one meter will not coincide with the numbers from another manufacturers meter. A concrete moisture meter will not give a proper reading over wood and the same applies to wood meters over concrete, each type of meter is designed for a specific use and function.

Are the meters used in situations where they are exceeding the recommended limits of their use?

Yes, when inspecting an installation that has wood installed over a concrete substrate, individuals have used either a dielectric wood or dielectric concrete meter, you can use either meter but remember that you will need to find an unaffected area to get a relative value to help determine the value of the affected area. Dielectric wood meters will register a higher moisture content reading if reading through both wood and into the surface of the concrete whereas, a dielectric concrete meter will register a lower moisture content reading when reading through wood to the concrete surface. Also, keep in mind that this is a questionable qualitative test, it is just a relative reading to determine if there is more moisture in one area than another and does not give an exact moisture content due to reading the mix of materials.

Here are some tips when using meters

• Make sure you understand the specifics of each manufacturer's meter as they have their differences.

• Readings on the wood meters generally read from 6 percent to 27 percent for the Capacitance meters, and from 5 percent to saturation point, 30 percent on the dielectric meters.

• Make sure there is no surface moisture present prior to testing as it can skew the results.

• Pins, on pin meters MUST be in new like condition to measure accurately.

• When using conductance meters with pins that are driven into the wood material, if it is an installed product, make sure you request permission to use this type of meter as it is intrusive testing and will leave permanent holes where the pins are driven.

• Understanding the depth at which the meter reads is important as they are calibrated to a certain depth, both wood and concrete meters.

• Follow the manufactures guidelines for temperature operating range.

• Wood Meters- Check with the manufacturer to see if meters are to be used parallel with the grain of the wood or if orientation of the meter is not affected by grain direction.

• Know the size of area the meter is reading.

• Make sure you are getting full contact with the substrate being tested.

• Document, document, document; this is critical if there are any issues in the future.

Remember, if you are providing a quality product and professional installation, and fail to conduct a moisture test, it does not matter how good the product or the installation, if it fails due to moisture that was not checked and documented prior to installation either by you but preferably, an independent third party, the entire installation would be considered a failure from the beginning. Without moisture testing documentation, the liability can still fall on the installer, even though the installation procedures may not have been a contributing factor to the actual cause of the failure.