- THE MAGAZINE
Visible signs of water damage and moisture intrusions are easily recognized. When mushroom grow on a carpet or the ceiling is black from mold, it is clear that those materials have to be replaced. However, it is always harder to determine the level of invisible water intrusions in a building. The restoration specialist has to rely on a moisture meter to determine where and how deep moisture has infiltrated into the building envelope. Using moisture meters to their full ability and knowing about the limitations of each type allow for making a competitive quote and being able to finish the job with a high first-test pass rate.
Moisture meters for the restoration specialist come with different measuring technologies. Pin meters, non-invasive, or pin-less meters, and RH meters are available as separate units or as combination meters. Each one of these technologies has its advantages and its limits and a careful examination of the problem on hand will allow for choosing the correct mode.
Pin meters measure the electrical resistance between two metal pins. The highest moisture level within the small measuring field is indicated. Hand-held pin meter with built-in pins usually allow a maximum measuring depth of ½”. They easily indicate different moisture levels in different locations, but they do not differentiate between surface moisture and moisture at the ½” level. If the surface is wet, that is what the meter indicates.
It is necessary for many applications to measure deeper into the building envelope than ½”. How otherwise can anyone find out, if there is a problem in the structural components of a building behind the wall coverings? Depth measurements can also deliver important clues to where the source of the problem is located. Different attachments are available for most pin meters to allow a greater depth of measurement. However, true readings from the depth of penetration can only be obtained if the pins used in the attachment are insulated. The insulation is absolutely necessary, because the measurements of insulated pins are only taken from the tip of the pin at the exact depth the pins have been driven to. Slide hammer electrodes have been used for a long time in the hardwood flooring industry. They allow for checking a sub floor without removing the floor planks. Hand probes with long pins have also been around for quite some time to check moisture in walls, especially for EIFS evaluations. Neither pin-less meters nor thermal imaging cameras can indicate excess moisture buried in the building envelope. Even though pin meters leave two holes and are sometimes cumbersome to use, they can give important information no other moisture measuring method can provide.
So why does anyone even use pin-less meters? The answer lies in the speed at which measurements can be obtained of a large area without leaving pinholes.
Most pin-less meters use the capacitance method, where measuring pads at the backside of the meter have to be pressed against the surface to produce a measurement. One moisture value is indicated for the entire measuring field. From the geometry of the measuring area it becomes apparent that moisture closer to the surface has a greater impact on the average moisture content than the moisture closer to the depth of penetration. The standard measuring depth is ¾” deep and the moisture of all materials within that area is included in the indicated value. There are also dual-depth meters, where the measuring depth can be changed between ¼” deep and ¾” deep. Switching to the ¼” depth allows for accurate measurement of thinner materials and to measure moisture close to the surface versus moisture in the entire measuring field. For instance, when a hardwood floor or other floor covering over concrete is measured, the ¼” depth measurements are accurate because the concrete is not within the measuring field. However, for any pin-less meter, the given measuring depth is how deep the measuring field reaches and moisture beyond is not measured.
Pin vs. Pin-Less Meters
Comparing both methods, pin meters look down and pin-less meters look across walls, floors or ceilings. Pin-less meters can scan large areas fast. Pin meters can be used for in-depth evaluations.
The above-mentioned measuring methods work great for wood, drywall and many other solid materials. Concrete slabs, screeds and fluffy insulation are an exception.
A relatively new RH in-depth moisture test is now recommended to determine if a concrete slab is dry enough to install a floor covering. Many manufacturers of resilient and textile floor coverings, coatings and adhesives require this test. The RH test does not measure the moisture in the concrete, but measures the moisture evaporated from the concrete. In reality, the moisture evaporating from a slab is the moisture, which will affect the floor covering. Pin and pin-less meters are not reliable enough to determine if a floor covering can be installed. ASTM standard F2170 describes the RH test.
Pin and pin-less meters cannot be used to measure moisture of insulation - a solid material with a stiff surface is required. However, a good way to evaluate insulation is with an RH test. RH probes embedded in the insulation will indicate high or low humidity levels. If the surrounding air is cut off, only the humidity within the insulation will be measured. Thirty to 50% relative humidity is a healthy inside living condition for people and 65% is the general threshold for mold growth.
RH probes used in the concrete test have to have an accuracy rating of +/- 2% for values below 90% and +/- 3% for values above 90%, which also makes them very suitable for ambient humidity testing. Most instruments are set to indicate relative humidity, temperature, dew point and mixing ratio.
After deciding which meter to use, the final question is what does the value on the display actually mean. Every material with a different conductivity and with a different specific weight will produce a different moisture value. Most meters are calibrated for measuring different wood species, some also have specific calibrations for measuring drywall, gypsum and other materials. For those materials the number indicated on the display are true percentages. However, often no calibrations are available or layers of different materials are to be evaluated. The easiest way in dealing with this is to use the reference scale on the meter and to find a dry piece of the same composition of materials. A base value can be established by taking a reading of the dry material. The number indicated on the display is not a moisture percentage but a relative value. Whenever the same materials are tested, the indicated value can be compared to the base value for dry. This method works for both pin and pin-less meters.