• David Newman

Flat Is the Key for LVP

I have noticed a large increase in the amount of flooring failures related to the subfloor or substrate not being flat to the tolerances stated in installation guidelines for the respective product. I feel much of this is due to the growing popularity of click joint style luxury vinyl plank flooring (LVP).

These failures have involved gapped joints, hollow sounds, creaking noises, and flexing of the material over substrates that revealed no measurable deflection. The vast majority of these involved on grade concrete slab foundations but there have also been some wood panel constructed raised foundations over crawl spaces, and substrates on levels above the entry level, where these types of issues were evident.

First let’s define flat versus level. Webster’s dictionary defines these terms as the following: Flat - having a relatively smooth or even surface; Level - the plane of the horizon or a line in it; to make a line or surface horizontal. Consider a ramped walkway up to a building. The ramp can have a flat surface but will not be level as it will be sloped from a level plane. If this same surface has excessive ridges, domes, or depressions then it will not be flat.

The American Concrete Institute (ACI) states a tolerance for flatness of a concrete substrate at ¼ inch in 10 feet. A common industry tolerance from flooring and adhesive manufacturer’s for flatness of a surface to receive flooring is 3/16 inch in 10 feet or 1/8 inch in 6 feet spans when installing using adhesives. The National Wood Flooring Association (NWFA) states that when nailing down a wood floor the subfloor should be flat to within 1/4” in 10’ or 3/16” in 6’, but 3/16” in 10’ when installing with adhesives. It is the responsibility of the flooring installer to assess and address substrate flatness before installation. I’ve read manufacturers guidelines stating tolerances on spans measuring 3’, 4’, 6’, and 10’ and height variations measuring from none to ¼”. Every manufacturer has their own guidelines and specifics as to installation of the product. Many manufacturer’s state that installation of a flooring product constitutes acceptance of the subfloor conditions at the time of installation.

Instances where a firm material, such as engineered wood flooring, is being installed via the glue down process atop an on grade concrete slab foundation that is not flat to tolerance can result in hollow sounds and possibly deflection of the material. I had a contractor hire me to provide confirmation that the concrete substrate was ready to receive the engineered wood flooring they were going to install. Besides testing the slab foundation for pH, vapor emissions, and porosity, the slab was also assessed for flatness. There were drops in the slab foundation discovered measuring from 6/32 inches to 12/32 inches in 6 foot spans. I had to return 3 more times to assess the flooring for flatness before they had achieved the flatness tolerance of the flooring manufacturer of 1/8 inch (or 4/32 inch) in 6 foot spans. Most adhesive manufacturer’s recommended trowel has anywhere from 1/8 inch to ¼ inch depth to the notch, with the adhesive product being used for this installation requiring a ¼” x 3/16” V notch trowel. Any drop larger than 8/32 inches could easily result in the flooring never making contact with the adhesive, creating hollow sounds. This type of condition is commonly not detectable on raised wood panel substrates as they always emit a hollow sound.

Installations affected by flexing of click joint style wood flooring planks, laminate flooring, or LVP flooring materials, commonly reveal drops in the flooring surface well beyond the manufacturer’s tolerance for flatness. Flexing can occur when planks are placed to where they cross a high point and the joint is located in a low point. Excessive or continual flexing can result in creaking or squeaking noises to wood based products with application and removal of loads, as well as damage to the milled click joint. Some LVP flooring can also create noise with excessive flexing.

Shows an area of a laminate installation where the consumer was concerned with excessive flexing of the flooring. When one walked in front of the cabinet, items on it would wobble.

A 10 foot screed was placed across this area which revealed a drop in the flooring measuring 11/32 inches in this 10 foot span.

It seems virtually every instance of inspecting an LVP flooring for end joint gaps installed via the floating process reveals the floor surface to not be flat, with drops discovered measuring from 7/32 inches to 20/32 inches in 10 foot spans. Commonly there is also flexing of the material in these areas due to the drop in the substrate not providing a solid base or surface directly beneath the flooring planks. Many of these planks are only 2 to 5 mm in thickness which leaves very little room for excess movement before the click mechanism between the 2 adjoining planks becomes dislodged. Flexing in these joint areas can also cause breakage of the milled joint.

Say you’re installing a 3 mm thick product (about 4/32 of an inch) yet a drop in the substrate beneath an end joint area measures 6/32. That enables more than enough flex in the material to dislodge the groove side from the tongue side of the respective planks. Imagine if this circumstance is located in a main pathway, how many times that end joint will incur loads. Obviously the rigidity of the material plays a big factor in this scenario.

Shows end joint gapping of a click joint style LVP floor.

Shows a drop in the flooring in this area measuring just under 15/32 inches in a 10 foot span.

These photos show a laminate floor where the plank with the groove click joint end depresses under a load due to a void or depression in the substrate beneath the material.

There are many ways to check the flatness of a substrate or subfloor. Lasers, string lines, straight edges or levels, are the most common. Personally I use a 6 foot metal level and 10 foot metal screed. Another way to check for flatness is through the use of Ff and Fl numbers, but that is another process all on its own. Do yourself a favor. If you’re installing a floor, or having a floor installed, make sure the substrate or subfloor is flat to tolerance prior to installation. The installation contractor should do this but a third party independent flooring consultant / inspector can also provide documentation as to the condition of the surface to receive the flooring prior to installation.

David Newman

Newman’s Flooring Services