The moisture meter you use completely depends on what you’re trying to accomplish. For a contractor/installer of wood flooring, a pin meter is considered by many inspectors to be the meter of choice, although a non-invasive meter can also be used. A pin meter set to the proper wood species and temperature will give you the proper moisture content (+/- 1%). Using that same meter on a wood subfloor (adjusted for subfloor type) will provide the moisture content of the subfloor.  According to the National Wood Flooring Association (NWFA), the difference between a solid strip board (under 3” wide) and the subfloor cannot exceed 4% moisture content.  A solid plank (3” wide and over) cannot exceed 2% between the subfloor and board plank. FYI, if these parameters are not met, rest assured an inspector will be called to the job not long after the installation is completed to inspect the floor for cupping.

According to the NWFA all prefinished floors must be manufactured between 6 and 10% moisture content, and all unfinished wood must be manufactured between 6 and 9% moisture content. If you’re reading these floors with your pin meter (or non-invasive meter) and the readings are 11% or higher, then the floor has not completely acclimated. If that floor is installed, again expect an inspector to be called out, this time for a potential gapping claim.

If readings are below 6% and the floor is installed tight, cupping or buckling could be a potential problem. The cupping is more than likely permanent and called acclimation cupping. If the floor is installed tight and is under its normal 6 to 10% moisture content the boards will grow in width once the floor reaches the proper moisture content. At that point being installed tight, the only direction the floor can go is up, causing acclimation cupping. In rare instances if the flooring is extremely dry when installed, the gain of excessive moisture to normal moisture content can potentially cause the flooring to buckle off the subfloor.

Moisture meter readings are also needed for concrete subfloors prior to installation of most hard surface flooring and some vinyl-backed carpet. There are also various moisture meters available that can be used to test the moisture content of concrete subfloors. For concrete, ASTM F2170 Measuring Relative Humidity Testing in Concrete Floor Slabs (RH Testing) is slowly becoming the contactor’s choice for reading moisture in concrete. The RH meter when properly used provides the percentage of moisture in the concrete. Most hard surface flooring manufacturers publish limits on moisture percentages in which their product can be installed. By performing proper moisture testing you can determine if a moisture barrier/retarder needs to be applied over the concrete prior to installation to meet the manufactures requirements.

Along with concrete moisture meter readings, a pH reading always needs to be taken. Believe it or not there are also meters that can be purchased for reading the pH in concrete versus the old-school pH paper, paint or markers.

Why, why, why do you have to take all these meter readings with the concrete? Well, the short answer is to ensure a successful installation and avoid receiving an inspector’s report asking if you would like some salt and pepper with that job you’re about to eat, because you didn’t perform the simple tests needed.

The long answer is, a combination of potential problems that may cause the installation to fail:

  • Too high of pH levels on concrete will degrade all adhesives and cause the installation to fail. Hence the salt and pepper statement!
  • Too high of a moisture content in concrete will cause the adhesive to liquefy and again cause the installation to fail.

I am an inspector that has seen each and every one of these situations occur more than once. Helpful hints: The best form of insurance you have to CYA is documentation.  Use your camera phone and installation paper work with the consumer’s name, address and phone number. Today’s camera phone technology captures clear pictures of any meter readings next to the consumer’s paperwork, and keeps it all together for your records. This is your get out of jail free card! These photographs prove you performed your job properly and if there are any moisture-related failures, they were not present at the time of your installation. Therefore, they must have occurred post-installation!