Substrate moisture is the leading cause of LVP installation failure in multifamily construction, and it is one of the most consistently underperformed pre-installation steps. The flooring sub who installs LVP over a concrete slab without performing and documenting moisture testing has installed over an unknown substrate condition. When the floor buckles, gaps, or shows mold beneath the planks after move-in, the absence of pre-installation moisture testing documentation leaves the GC exposed to a warranty claim without the documentation to challenge it.
LVP is waterproof on its face. This is the source of the most common misunderstanding about moisture testing for LVP installation. A waterproof wear layer does not mean the slab moisture condition is irrelevant. Moisture migrating upward through the concrete slab affects the adhesive bond in glue-down LVP applications, creates hydrostatic pressure under floating LVP that can cause buckling and joint failure, and in severe cases contributes to mold growth at the interface between the slab and the flooring system. None of these failure modes require moisture to penetrate through the LVP. They require moisture beneath it.
ASTM test methods for concrete slab moisture
Two ASTM test methods are accepted for concrete slab moisture measurement in LVP installation. Most LVP manufacturers specify one or both as the acceptable test method in their installation documentation. Installing without a test method accepted by the manufacturer voids the warranty.
ASTM F1869: Calcium Chloride Test. A sealed calcium chloride dish is placed on the concrete slab surface for 60 to 72 hours. The moisture absorbed by the calcium chloride is measured, and the result is expressed as pounds of moisture vapor emission per 1,000 square feet per 24 hours (lb/1,000 sf/24hr). Most LVP manufacturers specify a maximum acceptable emission rate, commonly 3 to 5 lb/1,000 sf/24hr for floating LVP and tighter limits for glue-down applications.
ASTM F2170: Relative Humidity Probe Test. Probes are inserted into holes drilled 40 percent of the depth into the concrete slab and allowed to equilibrate for a minimum of 72 hours before reading. The result is expressed as percent relative humidity within the slab. Most LVP manufacturers specify a maximum acceptable in-slab RH, commonly 80 to 85 percent for floating LVP. The F2170 method is generally considered more reliable than F1869 because it measures moisture within the slab rather than at the surface.
Both methods require a minimum equilibration period before reading and must be performed under the same temperature and humidity conditions that will apply during and after installation. Testing performed before the building is conditioned to its operational HVAC settings may produce results that do not represent the actual installation conditions.
Test locations and frequency
ASTM standards and most LVP manufacturer installation guides specify minimum test frequency by area. A minimum of three tests per 1,000 square feet is a common specification, with at least one test per room or defined area for smaller spaces. Additional tests should be placed in any area with suspected elevated moisture: near plumbing penetrations, at grade-level perimeters in garden-style construction, at crawl space interfaces, and at any area with visible efflorescence or staining on the slab surface.
On multifamily projects, testing every floor of every building is the complete standard. Testing a representative floor and extrapolating to unstested floors is not adequate, because moisture conditions can vary between floors and between buildings on the same site.
When testing results fail the acceptable range
When moisture test results exceed the LVP manufacturer’s acceptable range, installation cannot proceed until the moisture condition is resolved. The options, in order of preference:
Wait for additional slab drying time. Concrete slab moisture emission decreases over time as the concrete cures and as the building’s HVAC removes moisture. Retesting after additional drying time, typically two to four weeks, may produce results within the acceptable range.
Apply a moisture mitigation system. Epoxy or polyurethane moisture mitigation coatings applied to the slab surface can reduce moisture vapor transmission below the LVP manufacturer’s threshold. Moisture mitigation systems require specific application conditions and cure time before flooring installation can proceed. Confirm that the specific mitigation product is approved by the LVP manufacturer for use with their product.
Request a design modification. In cases of persistent high slab moisture, discuss the situation with the GC, the owner, and the architect. In some cases, a flooring product with a higher moisture tolerance, such as a glue-down LVP with a moisture-tolerant adhesive system, may be substituted if the slab moisture is within the alternative product’s installation range.
Documentation requirements
Moisture test results should be documented with the test date, the specific test method (F1869 or F2170), the test location (floor, room, and specific position within the room), the result in the applicable unit (lb/1,000 sf/24hr for F1869, percent RH for F2170), the tester’s name, and the result evaluation against the LVP manufacturer’s acceptable range.
This documentation should be submitted to the superintendent before flooring installation begins on each floor. The documentation is part of the project record that supports or defends any future warranty claims related to flooring performance.
How Innergy handles moisture testing
On every Innergy flooring project, moisture testing is performed and documented on every floor before installation begins. We use the ASTM test method specified in the LVP manufacturer’s installation documentation for the specific product being installed. Results are submitted to the superintendent before installation. If results exceed the acceptable range, we notify the superintendent in writing and do not proceed with installation until the condition is resolved. For LVP flooring as a standalone scope or part of a full seven-division package in TX, WA, OR, CO, UT, or NM, contact us and we respond within one business day.
The documentation from pre-installation moisture testing should be retained as part of the project record for the full warranty period. LVP manufacturers’ warranties typically run five to fifteen years for residential applications. A moisture-related failure claim arising two years after installation can be defended with pre-installation test documentation showing the slab was within the acceptable range at the time of installation. A claim against a project without pre-installation documentation cannot be defended on the same grounds.