Did an Improper Trowel Size Result in This Wood Floor Turning Black?

The dark gray areas formed a generally straight line.
The dark gray areas formed a generally straight line.

The dark gray areas formed a generally straight line.The dark gray areas formed a generally straight line.

The Homeowner's Issue

The flooring contractor installed a 5-inch natural maple engineered floor over new and existing slabs on grade in a 35-year-old home undergoing an expansion. One year after installation, the general contractor noticed one plank turning dark gray in the older section of the home. The homeowner and GC called the flooring contractor, and they decided to watch the discolored plank over the next few months. After more signs of discoloration appeared, they decided to have the wood floor inspected.

Roy: The Inspector's Observations

There were dark gray spots in the older section of the home. The builder said there was a vapor barrier under the new concrete but was not sure what was under the original concrete. The builder said other areas in the concrete beneath had been cut to install new piping (no piping leaks were detected). A plank was removed for inspection, revealing cracked concrete underneath. The plank's underside was black and had a strong musty odor. The installer said he used a two-in-one moisture control adhesive. Upon removal of the plank, it was apparent the installer used a 3/16-inch clip-on trowel. The manufacturer of that product requires a 3/8-inch clip-on trowel and flooring pressed firmly into the adhesive bed to ensure all ridges are compressed into a monolithic layer, as well as 100% coverage over the subfloor and transfer to the back of the flooring. The inspection revealed there was no monolithic layer of adhesive and that some areas had no adhesive transfer to the back of the flooring. The back of the affected flooring was 46% MC. I concluded that using the incorrect trowel size compromised the adhesive's moisture control properties. The floor installer also failed to recognize the cracks in the concrete and did not contact the adhesive manufacturer regarding a moisture suppression system.


RELATED: Why Is This Prefinished Wood Floor Rotting in Place?


Blake: The Attorney's Analysis

One thing I like about being a construction lawyer is that I'm always learning something new. In this case, I first had to learn what a "monolithic layer" was. I was also interested to learn that the size of the trowel used in applying adhesive is specified in manufacturer guidelines—information that would have been useful for this installer to know. He chose to use a "two-in-one" adhesive that includes both adhesion and moisture control, meaning the adhesive had to fully cover all of the concrete and the back of the flooring. He also apparently failed to inspect the concrete for pre-existing cracks. That error, coupled with using the wrong trowel size, resulted in excessive moisture developing under the flooring. The installer is now responsible for removing the furniture, pulling out the flooring, addressing the concrete issues and replacing the floors correctly.

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