Can there be moisture issues with waterproof LVT? The short answer is yes.
I recently received an email from a customer who had installed an LVT floor directly over concrete. Note: He is a novice installer, and he installed the floor as a favor to a friend. His neighbor, a general contractor, helped with the installation. He wanted to buy a pin meter from my company to measure the moisture in the concrete slab underneath the LVT floor, which had failed. Specifically, he had issues with the LVT floor buckling and he sent a photo to demonstrate the problem (see Figure 1).
In his email, he stated he had contacted the company that sold him the product and they sent an independent inspector to the home. The inspector who came to the site said he had never seen anything like it. They pulled off several base boards to show they had the proper clearance around the perimeter. The inspector placed a pin-less meter (not from Lignomat) on top of the LVT, set the meter to a drywall setting and the meter indicated 96%-100% (comparative scale). From those measured values the inspector concluded that the floor buckled because the moisture content in the concrete was over 75%. Subsequently, the manufacturer denied the claim due to too much moisture in the concrete.
From my point of view, there are many problems with this inspection and the conclusion that was drawn. Let’s start with the most obvious one: The value indicated by the pin-less meter is not a percent measurement; rather, the percent value from the in-situ probe test is a relative humidity percentage of air. The inspector should know better than talk about a 75% moisture value as a limit for concrete moisture measured with a pin-less meter through an LVT floor.
In seeking to give some advice to this distraught customer, I asked about the installation instructions and what the manufacturer requires as concrete moisture testing before installation. That information should shed some light on this value of 75% and also how this value is measured.
Unfortunately, the customer did not have the instructions any- more, but he stated it said “under 75%.” So I looked for an installation manual from a prestigious LVT flooring manufacturer and found the following: “All concrete slabs must be checked for moisture before installing material. Moisture emissions from subfloor cannot exceed 3 lbs. per 1,000 sq. ft. per 24 hours as measured with the calcium chloride test or in excess of 75% in-situ relative humidity. Responsibility for determining if the concrete is dry enough for installation of the flooring lies with the owner and installer.”
This is exactly what an instruction manual should look like. It gives the correct guidelines by setting a permissible range for a specific test method to determine whether or not a floor can be installed. Installers and inspectors should follow those guidelines.
Could that inspector be so confused about how to test the moisture in a concrete slab? Following the instructions in the manual, a 75% permissible moisture range is not for a pin-less moisture meter test; however, it is the permissible range for the in-situ probe test (see sidebar below). The in-situ probe test determines the relative humidity in concrete floor slabs. The test method is used as a quantitative determination (not qualitative or comparative) of relative humidity in concrete slabs as described in the ASTM standard F 2170. It is a test that requires drilling a hole in the concrete floor, setting a sleeve and inserting a relative humidity probe (see Figure 2).
The manufacturer states in the installation manual, that the moisture emission from the concrete slab should not exceed 75%. However, if the inspector uses that moisture value, he should have at least used the test method described in the manufacturer’s instruction manual to prove his point. There is no pin-less moisture meter nor a moisture range mentioned.
I advised my customer to either get an inspection service specializing in in-situ probe testing or to buy an in-situ probe test kit such as the BW-KS package, a Lignomat product. Note: I did not sell him a pin moisture meter to measure the moisture in the concrete slab, even though that still is a moisture measuring method used for concrete slabs.
But since the method is not approved by the flooring manufacturer and not mentioned in the manufacturer’s installation manual, any moisture measurements done with a pin meter would not have been relevant.
Grete Heimerdinger, vice president at Lignomat, has been heading the moisture meter division of the company since 1981, when the first pocket-size mini-Lignos were introduced.
