Engineered hardwood flooring is a product segment growing in popularity, with its value-driven price-point enticing consumers and its installation flexibility making it seem like a no-nonsense product for installers and contractors. We spoke with manufacturers of engineered hardwood flooring adhesives, installation tools and moisture meters to find out the best way to lay this type of floor down.

Adhesives. Gregory Wood, president of Advanced Adhesive Technologies (AAT), said the biggest mistake he sees installers and contractors make is not properly prepping the subfloor. “Making certain the subfloor is protected from moisture and is dry, according to the floor and adhesive manufacturers, is mission critical,” he said. “Engineered floors, while more stable than solid milled flooring, will be adversely affected by moisture.”

He added, “The most common mistake we see is the failure to make the subfloor properly flat. This results in claims that the floor isn’t bonded properly. Actually what results are hollow spots where the engineered flooring ‘pops’ as the floor is trafficked. The vast majority of callbacks could be eliminated if the substrate is flat prior to installation.”

The trend toward wider, longer planks makes subfloor flatness even more important. “More rigid flooring tends to bridge the undulation in the subfloor, creating increased chance for a ‘popping’ condition. Using an adhesive that has an aggressive green strength, extended residual tack and is formulated to maintain the trowel ridge integrity will aid the installer in dealing with marginal subfloors,” Wood said.

Dave Darche, Bona’s sales and market manager for adhesives, believes that moisture problems can be even more severe with engineered products than solid. “A solid that picks up excess moisture but never quite ‘lays back down’ can still be sanded and refinished. Depending on the thickness of the lamella, an engineered wood floor might deform just enough that a conventional sanding would completely remove the wear layer, resulting in a complete tear out and replacement.”

He said that gluing down engineered flooring, even where it could otherwise be stapled, nailed or floated, has some benefits including reduction in the IIC rating (impact transmission) from footfalls and other noises. Some adhesives can also pose problems, as they can etch a prefinished surface during installation. However, Darche added, “Many manufacturers have been able to address this concern with advancements in formulations. I believe that several engineered flooring manufacturers are [also] designing products that allow for increased application opportunities, not only from a visual perspective but a structural one as well.”

According to Eric Kurtz, Bostik hardwood product manager, not testing for moisture or choosing to install on a wet slab without adequate moisture mitigation can result in a range of problems including cupping, crowning, end-lifting, cracking and buckling.

While installing engineered hardwood as a floating floor is a popular option, “the biggest issues with floating floors include separations caused by the expansion and contraction of the wood with changes in humidity, and the louder ‘hollow’ sound when it’s not firmly attached to the subfloor, causing many installers to seek out sound-dampening underlayments.” Floating installations are also more difficult to achieve with wider, longer planks. “As planks get wider, most installers and often manufacturers will require gluing or nailing the flooring,” he said.

Larry Scott, DriTac vice president of field technical service, said that all wood flooring, regardless of construction, is susceptible to moisture fluctuations. “Every subfloor should be cleaned and tested for moisture vapor transmissions prior to the installation. The moisture reading should be recorded in the job folder for further reference if a problem ever arises.”

When exposed to adverse moisture conditions, “engineered wood will expand and contract vertically through the length of the plank, which can result in end lifting/peaking where the planks join. It can also raise the grain of the wood and crack the veneers. This is known as face checking.”

He sees substrate preparation as vital. “Subfloor preparation is always key for any installation. However, wider and longer planks require even more attention to substrate detail. The substrate must be flattened and smoothed to the recommended limitations of the manufacturers.”

Because of the cross-ply construction of engineered flooring, the signs of moisture damage in engineered products can appear different than those in solid, said Mark Lamanno, flooring technical market manager for Franklin International/Titebond. “End lifting, staining, delamination and face checking can all be attributed to moisture issues when moisture content exceeded the manufacturer’s recommended levels,” he said.

He added that while engineered flooring is designed to be installed on more substrates and in more ways than solid, there are still limitations. “It is incorrect to think that any engineered product can be installed in any manner available. Certain types of engineered flooring can be installed in all applications. Some cannot, based on the product. Some engineered flooring can be nailed or stapled, for example. Others cannot.”

Ron Loffredo, senior area technical manager for H.B. Fuller Construction Products/Tec, said installers working with engineered hardwood floors should “opt for an adhesive that contains no water, such as a moisture-cure urethane or modified silicone adhesive.”

When encountering any problems in a cement substrate, “voids or deflections should be filled with a cementitious patch or self-leveling underlayment. An improperly prepared substrate can cause installation failures,” he added.

Sam Biondo, MAPEI’s national presenter and senior technical services consultant, said engineered hardwood reacts differently than solid when exposed to moisture. “Because engineered hardwood has grains that go in multiple directions, expansion from moisture goes in all directions as opposed to primarily lengthwise for [solid] hardwood.”

Understanding acclimation is key to installing hardwood, he noted. “Here in South Florida a product may arrive at 6-7% while it must be acclimated to 12-13% to avoid expansion due to swelling, whereas in Arizona it would need to be acclimated to 3-4% to avoid gaps due to drying. The National Wood Flooring Association publishes ranges for certain areas of the country that can be used as a general guideline.”

Wider planks can also cause additional challenges. “A 1 percent expansion in a 2 1/2” wide plank is a small amount (less than 1/32”), whereas a 1 percent expansion in a 12” wide plank is not (almost 1/8”). While these different widths with these different finishes can challenge adhesives, for the most part today’s floors are among the easiest to install that we have ever seen.”

Sonny Callaham, Royal Adhesives & Sealants technical product manager, boils down the importance of acclimation. “For the most part wood is simple. If it is exposed to a greater moisture level than what was present at the time of installation the wood flooring will expand. If moisture is taken away from the wood flooring, then the wood will shrink creating gaps in the boards. Knowing and documenting the moisture level of the wood flooring at the time of installation will help resolve any claim issues that arise later.”

Choosing a product that is both an adhesive and moisture barrier in one is an easy, cost-effective way to install engineered hardwood, he said. “It allows the installer to install the flooring in the same time as a traditional glue-down installation and still offer the customer a moisture warranty.”

According to John Schutt, Southern Cross Building Products vice president of sales and marketing, using an adhesive instead of mechanically fastening or floating an engineered floor is a popular method. “The increase is partly due to concrete subfloors replacing wooden framing with plywood or OSB subfloors. In addition, many installers find they have fewer call backs for squeaks when installing with adhesives.”

He said adhesives containing “MS-polymers and ST-polymers [will] gain market throughout North America, as they have already done in Europe. Also look for urethane manufacturers to continue the evolution of their formulas to reach the low VOC levels and other characteristics of the polymers.”

Mark Long, Stauf USA technical director, said the choice on whether to float, glue, nail or staple the floor will depend on jobsite conditions and manufacturer recommendations. “Always go with the manufacturer-recommended method of installing the flooring,” he said. “Installers tend to do what the stores tell them to do, but the installers really need to know, since they are the last ones to touch the floor, what they are responsible for and what to do if something goes wrong. Read the instructions. Know what the floor is approved for.”

Tools and Moisture Meters. Renee Tester, Harris Wood/Q.E.P. product marketing and technical services manager, said acclimation is not always necessary with engineered flooring, but in certain climates and during certain seasons it can become essential. “In dry climates where the humidity runs below recommended levels, it is important the wood adjusts properly to the interior environment, which should always be maintained between 35-55%.”

As for installation methods, each have their advantages and disadvantages, she said. “Floating floors provide the most versatile installation options. Nail and glue-down installation provide a more sound and secure installation, with no movement underfoot, but can be troublesome if repairs or replacement is needed.”

When mechanically fastening a floor, tools available include mallet-actuated tools in manual or pneumatic versions as well as trigger-pull pneumatic tools. “When installing thinner engineered floors (3/8” and less), it is preferable to use a trigger-operated tool which is lighter and more delicate. Mallet-actuated tools are heavier and if striked with force, they can damage the edge of the board and could create peaking with the adjacent board,” said Curtis Richard, Primatech account manager.

He added, “If using a mallet-actuated tool, choose one that offers an adjustable front block which butts up against the tongue, thus keeping the fastener ejection area away from the top edge.”

Nails or staples are both fine choices for fastening the floor, Richard stated. “They are found in different thicknesses and lengths that range from 1” to 1 9/16”, although if installing a 3/4”, two-ply finger block core construction it could be wise to use a staple. Always follow manufacturer recommendations, and adjust and test the tool, and the size of the fastener, before beginning installation.”

Tom Laurenzi, Delmhorst Instrument Co. president, said acclimating the flooring three to seven days with a full functioning HVAC system can help ensure the product is ready for installation. “Moisture testing is just as important and required at time of delivery to the jobsite, during the acclimation period and during installation. Typical recommended ranges per NWFA are 30%-50% for RH and temperatures from 60 to 80 degrees Fahrenheit with the ‘ideal’ about 45% and 68 degrees. Both moisture meters and thermo-hygrometers remain indispensible tools no matter the product.”

According to Grete Heimerdinger, Lignomat product manager, “I believe every flooring installer would do themselves a favor by taking moisture readings. It does not matter if they are installing an engineered or a solid floor plank.”

She said readings should be taken at four points during the project: “when the floor is first delivered and taken out of its packaging, before acclimation, after acclimation and after job completion.”

She added, “The moisture should be checked with a meter. At the same time, the relative humidity should be measured and compared to the equilibrium moisture content (EMC) chart. True dual-depth meters can pinpoint any changes very accurately. We recommend for any flooring installation and inspection to take readings on both depth settings. Comparing moisture readings over time accurately reflects whether the moisture changes came from close to the surface or from the subfloor.”

Not everyone feels engineered flooring should be acclimated. According to John McCabe, an international consultant and forensic inspector for the wood flooring industry and speaking on behalf of Tramex, engineered flooring should only ever be acclimated if the manufacturer recommends it.

“The golden rule is you never acclimatize engineered wood flooring – you keep it wrapped in its original packaging until you are actually laying it. The reason is that some boards made with a softwood perpendicular core can pick up moisture very quickly, and as a result if the boards are open to absorbing moisture they will pick it up and expand. You then may have difficulty during installation when fitting the tongue in the groove. This is true of click systems also.”

More important than testing the floor is testing and measuring the environment the floor will be going into, he added. “Otherwise you are working blind.”

Jason Spangler, Wagner Meters flooring division sales manager, stressed the importance of following manufacturer guidelines. “Some manufacturers wrap their product in low-perm membrane inside the box, and want you to leave it that way until installation because of their drying process. Others want you to ‘rack’ the product on the jobsite for a period of time prior to installation.”

He added, “For the installer’s sake, understanding EMC, calculating it for every job environment, utilizing a reliable moisture meter with species/product specific settings to measure the finished floor and subfloor, and comparing those readings to EMC are what will lay a great foundation for the floor. This is when the floor is truly acclimated. If every floor started this way, it would be a huge step for the industry.”