Relative Humidity and Measuring Moisture for a Proper Wood Flooring Install
Thermo Hygro Meter - Moisture Meter
Why Is Relative Humidity Measured By Wood Flooring Installers?
Air, in our normal environment always holds humidity. The number of water molecules in the air can vary substantially, e.g. it can be as dry as in a desert or as humid as in the tropics. There is an upper limit to the amount of humidity which air can hold at a given temperature. Beyond this limit, saturation will occur. If for some reason the humidity level is pushed up to this limit, condensation occurs and fog or water droplets form. Relative humidity tells you what percentage of this maximum amount of humidity is present in the air. High levels of ambient humidity can be warning sign at inspection jobs, and RH is also a major concern when installing a wood floor over a concrete sub-floor.
The maximum amount of humidity the air can hold is directly related to the temperature of the air. If temperature rises or falls in a closed system, the saturation vapor pressure will increase or decrease. As a consequence, the relative humidity will drop or rise with temperature changes with an unchanging amount of water in the air.
When acclimating wood flooring prior to installation, it’s important to measure both the relative humidity as well as the moisture content of the wood flooring for a well done, long lasting, proper install.
RH Measurement Response Time
Response time is often quoted by manufacturers in the form of x seconds to get to 90% of the final relative humidity value. For example, if the RH is actually 80% and the manufacturer claims that the sensor will reach 90% of the final value in 45 seconds, that means the RH meter will read at least 72% RH (assuming it’s rising) after 45 seconds. That is still 8% RH away from the final value. It may indeed take 1-5 minutes to go to the rest of the way to 80% depending on the many variables that go into relative humidity measurements.
Response times will vary greatly under certain situations including:
moving air vs. static air environments
Age of the sensor
Chemicals or vapors present in the environment
A stand-alone thermo-hygrometer such as the Delmhorst’s HT-4000F is used by flooring installers and restoration contractors alike. Some people prefer a multi-function meter that includes a moisture meter and a thermo-hygrometer in one device. The TotalCheck and QuickNav 3-in-1 meters manufactured by Delmhorst Instruments are examples of multi-function meters.
Calibration
Calibration may also affect response time. When comparing two meters, although one may appear slower than the other, it is only because they are ending at different points. Even two meters in calibration may have an endpoint up to 4% - 6% apart.
Some wood flooring installers, contractors and wood flooring manufacturers might wonder how long the sensor calibration will last. Due to the fact that there are several causes for RH sensors to drift and/or fall out of calibration, there’s no definitive answer to this question.
How the sensor is stored, as well as the environment the sensor is used in both impact the life of sensor calibration. While one flooring installation contractor may find calibration still in tolerance after a year or more, another in a different environment may find drift after only a few months. At one point all sensors will lose calibration. All relative humidity sensors must be recalibrated or replaced periodically.
In-Field calibration checks for wood flooring installs can be done by comparison against a second reference sensor or using saturated salt solutions. For more about in-field calibration, proper operating and storage, and other critical factors to consider when comparing Relative Humidity readings, download our FREE Guide ‘Relative Humidity Sensor Behavior and Care’.
Delmhorst Instrument Company adheres to nationally recognized standards and practices and uses the most accurate equipment available. Each Delmhorst sensor’s calibration is NIST (National Institute of Standards and Technology) traceable and checked against a chilled mirror hygrometer.
For more information about the value of using a RH Sensor along with a Moisture Meter for the best in wood flooring installation, our specialists in Europe are available to advise. Feel free to contact us if you have questions.
