I recently had a conversation with another inspector about the accuracy of his moisture readings. He brought up a concern regarding elevated moisture readings on a wood floor that was showing signs of only slight cupping. The wood flooring in question was stained with True Black and finished with a water-based finish. The cupping was minor with this solid 3/4″ x 5” white oak plank being tested. He was getting readings in the 20 percent range, which generally would be accompanied by severe cupping or buckling. So, he asked me if I had run across an issue like that before. My response was no, but I suggested that he have his meters checked out. He sent his meter into the manufacturer, and all was well with them.
A few months later, I received a call from a local distributor in the Dallas area. The manager was asked to come out and trouble-shoot a cupping claim on some solid white oak plank flooring. The wood flooring contractor and the distributor each were measuring high moisture levels. They were getting readings in the mid-20 percent range where the cupping was located and low-20 percent where the wood flooring was flat. They knew that something strange was happening, but couldn’t put their finger on it.
The distributor asked if I have had, or if I have heard of any issues with measuring moisture content over darker stains, in specific, over True Black stain. It was at this time that I recalled previously having a conversation with another inspector, who relayed the same concerns. At this point, they asked if I could come out to assess the issue.
I had just received my moisture meters back from being factory calibrated and was sure I could get to the bottom of the high readings.
When I arrived, the homeowner, the builder, the distributor manager, and the installer were present to see if I could figure out why the moisture readings were so high. I began with my pinless meter, measuring at both 1/4” and 3/4” depths in an area next to the cupped floor. The readings at 1/4” measured 21.5 percent and at 3/4” measured 26.6 percent. This was in a flat area. I was concerned that I was having the same issues as the distributor and wood flooring contractor. So, I switched to my pin meter and had similar results. I then grabbed my hammer probe with insulated pins to see if I would get the same kind of readings at different depths.
Useful Tip from an Inspector: The carbon black in the True Black stain can cause additional connectivity and may give erroneous moisture readings for moisture meters commonly used by wood flooring professionals. The connectivity enhances or elevates the moisture reading two to three times higher than what the reading should be.
The tips of the pins have approximately 3/16” of exposed metal before the insulation, so I needed to drive the pins deep enough into the wood flooring to be past the stain and finishing materials to get a reading that seemed more appropriate, in the 12 to 13 percent range, but still higher than I expected in an area with no cupping.
After doing some additional moisture testing with the hammer probe and insulated pins into the plywood, I found elevated moisture readings in the 16 percent range where cupping was seen, and in the nine percent range where the wood flooring was flat. Once the moisture was detected in the plywood where the cupping was present, the affected wood flooring was removed. The flooring was repaired and then a complete refinish of the entire floor.
However, I was still curious about the abnormal readings over the True Black stain and three coats of gloss waterbased finish. I did some investigation into the erroneous moisture readings.
I contacted DuraSeal, the manufacturer of the True Black stain to see if they had heard of this situation and they stated they had not, but they would look into it and get back to me. A couple of days later, I received a call that stated the pigment color to achieve True Black is called Carbon Black.
I also reached out to several moisture meter manufacturers to get their take on these results. Although none of the manufacturers had come across this particular issue with True Black stain, they all agreed that pinless meters can be influenced by pigments with a carbon base, coal, or coal ash, and that the readings are always higher than expected. Similarly, the accuracy of pinless meters also can be affected by the metallic components found in some finishes (such as aluminum oxide).
Wikipedia states: “Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black, and thermal black) is a material produced by the incomplete combustion of coal and coal tar, vegetable matter, or petroleum products, including fuel oil, fluid catalytic cracking tar, and ethylene cracking in a limited supply of air. Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of activated carbon.”
Wikipedia states: “Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black, and thermal black) is a material produced by the incomplete combustion of coal and coal tar, vegetable matter, or petroleum products, including fuel oil, fluid catalytic cracking tar, and ethylene cracking in a limited supply of air. Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of activated carbon.”
Wikipedia also states: “The percolation threshold is a mathematical concept in percolation theory that describes the formation of long-range connectivity in random systems. Below the threshold a giant connected component does not exist; while above it, there exists a giant component of the order of system size.”
In layman’s terms, it means that the carbon black in the True Black stain can cause additional connectivity and may give erroneous moisture readings for moisture meters commonly used by wood flooring professionals. The connectivity enhances or elevates the moisture reading two to three times higher than what the reading should be.
With 45 years in the wood flooring industry and inspecting wood floors for more than 35 years, and being NWFA Certified Inspector since 2004, there’s always something new to learn.
Timothy McCool has 45 years of experience in the flooring industry, and is an NWFA Certified Wood Flooring Inspector. Located in Texas, McCool currently is a sales representative for MAPEI. He can be reached at tkmccool@gmail.com.
