Hardwood Floors August/September 2019

By Tony Morgan

Scientific research from leading academic and industrial institutions confirms the reliability and accuracy of the ASTMF2170 RH test at these depths. The readings will most accurately predict the slab’s point of equilibrium and, therefore, the true moisture condition that will exist within the slab after the flooring installation. How to Install Glue-Down Engineered Wood Flooring on Concrete Slab Preparation Slab preparation is critical for glue-down and includes sanding, scraping, leveling, and filling low spots because the slab must be flat so the planks can fit correctly. When leveling (actually flattening) a slab, according to the NWFA Installation Guidelines, don’t allowmore than a 3/16” difference in height within a 10' radius or 1/8” within a 6’ radius. Adhesives Before applying adhesives, you must fill in any voids or deflections in the slab with a cementitious patch or a self- leveling underlayment that is compatible with the wood flooring adhesives. An adhesive is not intended to fill voids or deflections. Use elastomeric adhesives specially formulated for wood flooring so they conformto the natural characteristics of wood – expanding and contracting.That is, their elasticity ensures that the engineeredwood has an ample amount of space to expand and contract without causing the glue to break its bond. Be advised: using thewrong adhesive or applying incorrect amounts can lead to a failed flooring installation. For example, use an adhesive that contains no water – like a moisture cure urethane or modified silane. These products are a good choice for these installations because they increase the strength of the bonding agent and offer a degree of structural flexibility. A glue-down installation requires premiumwood adhesives to be properly troweled over the concrete slab. Then the engineered wood planks can be laid into the adhesive and locked together at their tongue-and-groove joints. The adhesive manufacturer should have instructions regarding

ACCLIMATE ENGINEERED FLOORING Regardless of whether or not the flooring is glued, nailed, or floated, the environment needs to be aligned with the engineered wood flooring requirements before installation. It’s important to follow the manufacturer’s instructions for the proper acclimation procedure and timeline as these may differ from one engineered flooring brand to the next. Get yourself an accurate woodmoisture meter and use it to ensure the wood planks and the surrounding environment are properly aligned according to the manufacturer's specifications. There are two types of woodmoisture meters available: pin meters and pinless meters, the latter having nondestructive electromagnetic measurement capability. Another thing to check is the moisture condition of the concrete slab. Excessive moisture in a slab can damage any wood floor. Most flooring manufacturers require moisture tests for concrete moisture to validate their warranty requirements. Remember this: • Every concrete slab has moisture and will always have moisture. What you want is a slab with an acceptable level of moisture for the flooring you’re installing. • Besides the moisture already in the concrete, additional moisture can enter a slab from rainwater, poor plumbing, or drainage below or at the sides of the slab, and even humidity in the air. • To find out if your concrete floor meets the dryness criteria set by your flooring and adhesive manufacturers' instructions, remember this mnemonic: “If you wanna know, go below.” Scientific testing has determined that measuring the relative humidity (RH) conditions within a concrete slab yields more valuable data than only measuring the moisture evaporation emission rate (MVER) at the surface of the slab. To measure the moisture inside the concrete, you will want to conduct a test known as the ASTMF2170 in-situ RH test. The RH test uses sensors or probes to measure the RH at a specific depth within the concrete – 40 percent of the slab’s thickness for a slab drying from one side, or 20 percent for a slab drying from two sides. CONCRETE MOISTURE MEASUREMENT IS CRITICAL

the magazine of the national wood flooring association

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