*This article by INSTALL executive director David Gross was originally featured in ProInstaller Magazine.

Why Surface Prep Makes or Breaks LVP and LVT Installations

The callback comes weeks after the job is done. The luxury vinyl plank is beginning to show signs of failure. A ridge here, a soft spot there, edges lifting where they should lie flat. The customer is unhappy, the installer is back on site, and the product that looked fine at the time of installation is now the subject of a warranty dispute. Was it the product or the installation?

In most cases, the investigation reveals that it wasn’t a defect of the flooring plank product, but errors in the installation and often the surface prep underneath. Luxury vinyl products, specifically LVP and LVT, don’t hide substrate problems. They eventually reveal them. That means installers must be educated and understand how these products behave and what surface conditions and tolerances they require for a clean installation and optimal performance.

Three Things Installers Get Wrong About LVP and LVT

The luxury vinyl category has a reputation for durability and easy installation that has made it one of the most popular flooring materials on the market. But the qualities that have made it popular have also led to misguided beliefs about LVP and LVT that get inexperienced/undertrained installers into trouble.

Myth #1: It’s a waterproof product, so moisture is not a problem.

Reality: Luxury vinyl plank and tile are engineered with a waterproof wear layer on top that protects the decorative layer and core beneath it. But waterproof describes the surface, not the interface with the system underneath. Moisture vapor rising from the substrate below interacts with the backing, the core, and especially the adhesive in a glue-down installation. While the product itself is moisture-resistant, the adhesive and the substrate (especially concrete) are sensitive to moisture vapor and pH and depend on the right balance to keep the flooring material in place. Excess moisture can lead to a variety of problems, including mold, that can compromise cementitious patching compounds and cause adhesive re-emulsification, shifting, or lifting of edges.

Myth #2: LVP and LVT are flexible and forgiving, so the substrate does not need to be perfectly flat.

Reality: Many installers wrongly assume that resilient flooring products, whether sheet, plank, or tile, will drape and adhere to the substrate contours below. LVP and LVT are not manufactured to perform that way. These products are quite rigid and require a flat surface as defined by the manufacturer. The flatness of the floor is specified to provide consistent contact for adhesion and stability. Additionally, high or low spots in the subfloor may lead to uneven wear patterns. Subfloor deformities also make installation difficult, creating issues of run-off and misalignment that are unsightly and structurally problematic. In the case of a floating floor, low spots create unsupported sections that will flex repeatedly under load until the locking joint at both ends of the span separates or peaks. The failure often announces itself first as a hollow sound underfoot before it becomes visible at the surface. High spots create the opposite problem. The plank contacts the substrate only at the peak, rocking under foot traffic like a board on a fulcrum. Every step on one end drives the other end up, working the locking joints loose until the joints open or the edge lifts.

Whether glued down or floating, LVP and LVT require a substrate that meets the manufacturer’s flatness requirements to avoid these issues and protect the warranty.

Myth #3: It installs fast, so surface prep can move fast too.

Reality: The speed of LVP and LVT installation is often viewed as a genuine advantage for a fast turnaround, but it can create jobsite friction. GCs and homeowners who believe the floor can be installed quickly may not understand the entire process and that some critical components do not move at the same pace. This pressure is familiar to most installers, but it becomes a problem when it compresses surface preparation steps that cannot be shortened without consequences.

One example is newer wet-set versus older dry-set adhesive. Wet-set adhesives are demonstrating superior long-term performance over dry-set, pressure-sensitive adhesives of the past. However, wet-set adhesives require working off of the material, installing smaller sections at a time, and allowing the adhesive to set and cure by restricting foot traffic for a period after the installation is complete. This time must be accounted for and communicated properly during planning and scheduling.

Likewise, when installing on concrete slab, most flooring manufacturers either provide or reference ASTM F710 protocols, requiring the slab to be tested for moisture and pH before installing resilient flooring. One of the quicker methods is in-situ relative humidity testing per ASTM F2170, and it requires probes to be installed in the slab and left to equilibrate for a minimum of 24 hours before valid readings can be taken. This time allows the slab to reach equilibrium. A reading taken too early can be unreliable.

Each of these examples requires communication and coordination to be built into the installation schedule, so all stakeholders can plan accordingly. With an agreed upon schedule, an installer can comfortably adhere to the timeline and avoid any undue pressure from the GC or homeowner to move faster.

The Readiness Gap

When installers arrive on the job site, they are the ones who have the final go or no-go decision to make. Assuming an installation surface is ready, as determined by the general contractor or homeowner, is not sufficient. What ready means to a GC or project owner often has little to do with what ready means for installing the flooring material.

The concrete slab is a prime example of this readiness gap. Slabs are typically delivered to flatness standards set for general construction, measured very shortly after initial placement. ASTM E1155 is the test method used to measure floor flatness (FF) and floor levelness (FL) values, and ACI 117 establishes the concrete placement tolerances. Flooring contractors generally evaluate substrate suitability under ASTM F710 and manufacturer requirements using straightedge measurements rather than FF/FL numbers.

This distinction is often at the heart of disputes. A slab can meet ACI 117 FF/FL requirements yet still require patching or leveling to satisfy the flooring manufacturer’s flatness requirements. Typically, LVP and LVT manufacturers require flatness tolerances between ⅛” to 3/16″ over 10′ or tighter. Regardless of who declares the project ready, the installer assumes the final risk when work proceeds. Failure to independently verify substrate conditions can leave the installer financially responsible for flooring failures while exposing the end user to unnecessary disruption and frustration.

This responsibility applies to all substrates, from concrete slabs and wood subfloor systems like plywood and OSB to old sheet vinyl, VCT, or hardwood in renovation scenarios. Every surface comes with its own assessment and preparation requirements as dictated by the flooring product manufacturer and industry best practice, and none should be left to the judgment of a party who bears no responsibility in the outcome.

Two essential assessments for every LVP/LVT installation are:

Flatness. A flatness assessment establishes whether the substrate meets the tolerance stipulated by the manufacturer or ASTM F710 compliance. Importantly, flat is not the same as level. A floor can slope and still meet manufacturer requirements if the surface variation remains within the specified tolerance. Plank and tile manufacturers are concerned primarily with abrupt elevation changes, dips, ridges, and other surface inconsistencies that create stress points, movement, or visible defects in the finished floor. Any deviation beyond manufacturer specification must be corrected before installation proceeds.

Moisture testing. For concrete substrates, industry-standard tests include the relative humidity test per ASTM F2170, which measures moisture conditions within the slab, and the calcium chloride test per ASTM F1869, which measures moisture vapor emission from the surface. pH testing per ASTM F710 is also critical, as high alkalinity can degrade adhesives and cause discoloration in luxury vinyl over time. For wood subfloor systems, moisture meter testing in both pin and scan modes establishes whether moisture content is within the range the manufacturer specifies.

Best practice is to verify these conditions independently. If results fall outside manufacturer specifications, installers should document what they found, communicate it to the GC or homeowner, and not proceed with installation until the substrate is corrected. If not corrected, the manufacturer’s warranty most likely will be void, and the liability will belong to the installer.

Every assessment, every test, and every measurement is an attempt to reduce variance because in flooring installation, variance is risk. Accurate assessment also drives accurate job costing. The scale of flatness deficiency determines what corrective measures will be taken. The extent of a moisture problem can aid uncovering the source of the infiltration such as improper site drainage, non-conforming slab conditions, or contamination issues over and above the presence of a vapor emission or moisture content problem and direct additional mitigation requirements. Ideally, a bond test should also be performed to verify the compatibility of all components.

Fix It Before You Floor It

The range of conditions an installer must be prepared to address and verify is significant. Flatness deficiencies alone vary by substrate material, location, and scale. High spots may be ground down. Isolated low areas may be filled with a patch compound. Broader flatness issues across larger areas may justify a self-leveling underlayment (SLU). The method follows the condition, and it is not uncommon for multiple approaches to be used on the same job, each requiring its own product knowledge, mixing ratios, application technique, and cure time.

Moisture conditions add a layer of complexity. For excess moisture vapor or relative humidity in slabs, options include surface-applied epoxy or urethane coatings that create a near-impermeable barrier between the slab and the flooring system. The growing category of SLUs now also includes moisture-blocking compounds that consolidate mitigation and leveling into a single application. These product categories are not interchangeable. Moisture loads vary, and manufacturer specifications differ. An installer must understand both to select and apply the right system. Assuming that one product or system performs identically to another with a similar description can be a costly mistake.

Renovation and retrofit work introduce additional variables that further complicate substrate preparation. In residential remodel projects, existing sheet vinyl, hardwood flooring, adhesive residue, and other legacy materials may remain, creating height differentials, bonding concerns, and flatness issues that compound existing substrate deficiencies. In some cases, a well-adhered and secure existing floor may be left in place when removal is impractical, cost-prohibitive, or presents safety concerns, requiring the use of specialty underlayments and primers designed for non-traditional substrates. These products carry their own substrate preparation, compatibility, and application requirements, adding another layer of complexity to the installation process.

Despite all of these solutions, installers too often do things the same way they always have, using the same old off-the-shelf products, which is problematic in our rapidly evolving industry. Surface prep products, flooring materials, and installation skills are increasingly customized to provide specific solutions to specific problems, making training and certification from organizations like the International Standards & Training Alliance more of a necessity and less of an option.

The substrate conditions and surface prep scenarios described here are not unusual complications or rare edge cases. They are routine issues that installers encounter every day on luxury vinyl plank and tile projects. What separates a successful installation from a costly callback is not whether these conditions exist, but whether the installer has the training and experience to identify and correct them before installation begins.

Luxury vinyl flooring can beautifully cover a lot of problematic substrates, but not without expert installation. If there’s one thing every installer can count on, it’s that mistakes underneath never stay hidden.