Why are we moisture testing?
In my area, many installers believe that putting an impedance meter on the concrete floor in several areas is an effective indicator of moisture. They also believe that a couple pokes of the plywood with an “electrical resistance meter” is also an effective way to determine if the job is a go or no go due to moisture. There is also a large group of installers who don’t feel that moisture testing is necessary at all. And this is often based on the science of “I’ve never had a moisture problem”, or even better, “the slab is old so it is cured and dry.” So my question is why even do it. I’m currently working on an inspection 2000 square feet of a cupped 3 ¼” solid oak nailed to plywood on a second floor. The installation manager said that they tested 5-6 areas and the moisture was “fine” at the time of install (no documentation/pictures). During my inspection, my hammer probe indicator that the subfloor was 18% and the wood flooring was 12%. When I walked around the outside of the home I found open vents to the space between the 1st floor (garage) and the second-floor living space. The installation manager said no reasonable installer is going to check and see if there are open vents between floors. The general contractor was also unaware that the vents were present. The NWFA (National Wood Flooring Association) installation guide section 1 Chapter 3 states: “Test for moisture at several locations in the room – a minimum of 20 per 1,000 square feet – and average the results. Document all results. A high reading in one area indicates a problem that must be corrected. Pay special attention to exterior and plumbing walls.” In my opinion, if the installer had done 40 readings in multiple areas of the project it is highly likely that he would have found several areas that gave “odd” readings and then would have done some investigation to determine the cause. If he did properly test and properly documented the readings (pictures) and provided a copy of the moisture readings to the end user, if a moisture imbalance was found later, it is likely that the failure would have pointed to a site related problem, not installation.
Similarly, Impedance meters on concrete are a good indicator of moisture near the surface of concrete but are less indicative of moisture content and movement. I hear installers tell me, “if my readings are below 3 the slab is fine”. While the NWFA and most adhesives require some form of quantitative moisture test most of the testing that is being done is qualitative. Yes, I know there are adhesives that “don’t require moisture testing”. These adhesives must be installed differently than the adhesives we used to use, and many installers are failing at applying them correctly.
So if the testing that we are doing is not complete why even do it?