Failures Unique to Engineered Wood Flooring

Our industry is defined by floor coverings made of real wood. Real wood floors include both solid wood floors and engineered wood floors. The common denominator is that they’re both “real wood.” Engineered wood flooring makes up more than half of the wood flooring sold and put to use in our industry. Having a general appreciation of features and limitations of both solid and engineered wood flooring is a necessity for those working in the world of wood floors, specifically when it comes to understanding how they both perform. Both types of these wood floors respond to the environment in which they’re placed. However, some respond much differently than others simply due to how they’ve been constructed.

Engineered wood floors can be much more complex than their solid counterpart simply because they vary greatly in their construction from manufacturer to manufacturer and from product to product. Because of these differences, it is nearly impossible to place all engineered flooring into one simple category related to how they should be installed or how they will respond to a change in environment. These construction differences may include some or all of the following: species of the wear layer, cut of the wear layer, width and thickness of the overall product, number of plies, core material type, backing material, adhesives used, construction method, moisture content of each layer, balanced and unbalanced construction, and more. All of these variables affect how the flooring will perform, and help determine in which types of environments it will perform best.

The recently published 3rd edition of NWFA Problems, Causes, and Cures (Technical Publication C200) explores some of the issues that impact all wood floors, their causes, and potential cures. The following highlights some of the more-common issues that are unique to engineered wood floors.

Dry Cupping is a concave or dished appearance of individual engineered flooring planks with the edges raised higher than the center. Causes for dry cupping may include the following:

• When relative humidity levels remain below the manufacturer’s recommendations for long enough, engineered planks can begin to dry cup. When this happens, the top lamina/wear layer loses moisture and begins to shrink across its outer face, which can exert enough force on the core material to pull the edges of the plank upward. This causes a cupped appearance across the width of the board.
• In severe cases, layers within the plank may separate from one another when stresses exceed the strength of the wood flooring material itself, resulting in ply-separation. This is most common in dry regions and during dry seasons.
• Inadequate or inoperable HVAC systems resulting in elevated humidity levels.

Wood Shear occurs when external stresses exceed the strength of the wood fibers within an individual plank of engineered flooring, resulting in the wood fibers being torn apart. When examining this type of failure in an engineered wood flooring plank, wood fibers will be visible at the point of separation, remaining bonded to the adhesive layer. Causes for wood shear may include:

• Layers within the plank shrink or swell excessively because of low relative humidity or excessive moisture (outside of manufacturer’s recommendations), thereby creating excessive force on opposing layers sufficient enough to tear the wood fibers apart.
• Inadequate or inoperable HVAC systems resulting in elevated humidity levels.

Delamination/Glue-Line Separation occurs when there is a separation of two layers/plies within a piece of engineered flooring due to the lack of an adhesive bond. This is typically identified as a clean separation at the glue-line. Adhesive bond failure is unrelated to inadequate relative humidity levels. Causes for delamination/glue-line separation may be either of the following:

• Manufacturing-related; where the veneers are not bonded together due to improper or inadequate adhesive application, missing adhesive, dried or uncured adhesive, or steam pockets.
• Site-related; where extended or repeated exposure to standing water (flooding) has occurred.

Telegraphing Core Material is a visible pattern on the surface of the engineered wood floor plank that resembles variations in the core material of the product. Causes for an engineered floor that exhibits telegraphing of the core material may include the following:

• A gain or loss in moisture, causing wood fillet/finger block core materials to change dimension, which can then telegraph to the surface of the plank.
• Skips, voids, missing/open knots, or overlaps within the core material, telegraphing to the surface of the plank.

Endlift/Ski is a condition where the ends of installed engineered wood flooring boards deviate from the flat plane and appear raised or curved upward. Causes for endlift/ski may include the following:

• Flooring incompatible with the environment in which it is installed.
• Engineered flooring that has experienced an increase in moisture, where the core material running perpendicular to the face of the board swells at a different rate and in a different direction than the adjoining layers, forcing the ends of the material to lift, which can then telegraph to the surface of the plank.
• Inadequate or inoperable HVAC systems resulting in elevated humidity levels.
  Improperly selected, improperly installed, or improperly applied moisture control systems (vapor retarders) that do not provide adequate protection from below the floor.
• Maintenance-related:
  • Wet-mopping resulting in standing/topical liquid moisture left on the floor.
  • Use of steam mops/cleaning devices.
  • Use of non-breathable rugs on the floor.
  • Not maintaining relative humidity levels year-round to support the installed flooring.

Veneer Sand-Through is just what the title infers: when the top/wear layer veneer (lamina) of engineered flooring has been completely sanded through to the core layer. There is only one cause for veneer sand-through:

• Sanding of an engineered wood floor beyond the thickness of the top wear layer of wood to the core layer.

Lathe Checks occur in engineered flooring with rotary peeled or sliced face veneers. As the knife separates the veneer from the log, the separated sheet of wood is laid flat where stresses can occur in the region near the knife edge. If the strength of the wood is exceeded, this stress is relieved by separations (or checks) of the wood fibers parallel to the grain of the veneer at the knife edge. The knife edge of the veneer is known as the open (or loose) side, and the opposite side of the veneer is known as the closed (or tight) side. Lathe checks are not normally visible on the face of the finished board. Causes for lathe checks in engineered flooring may include the following:

• Lathe checks may become apparent/transfer to the surface with failure to maintain the ambient interior conditions specified by the manufacturer for the life of the product through all seasons. Loss of moisture or inadequate conditions post-manufacture can expose/generate fractures in the face veneer/lamina at any time.
• Excessive and rapid fluctuating environmental conditions from above or below the floor can cause stresses in the veneers sufficient enough to cause fractures in face veneer at any time.
• Lathe checks may develop or become apparent under any of the following circumstances:
  • Improper maintenance practices.
  • Improper management of direct heating sources, such as underfloor radiant heating systems, surface heat from uncovered windows, or near heat registers.
  • When the floor is covered post-installation with impermeable floor protection, exposing the floor to conditions outside of the manufacturer requirements.
  • Hand-scraped products that have been scraped too deep exposing the lathe checks.
  • Inadequate or inoperable HVAC systems resulting in elevated humidity levels.
• Manufacturing-related:
  • Damage caused during the slicing of the face veneer by the knife, by the pounding action of dull knives, knives with too small of a clearance angle, or excessively jointed knives.
  • Excessive pressure by certain machine parts such as feed rolls, pressure bar, or a chip-breaker can also cause this cracking in the wood.
  • Face-checks may become apparent when the manufacturer inadvertently installs this side of the veneer upside down (or face up.)  This is a rare occurrence and can only be verified by close examination of the cell structure of the exposed substrate of the face veneer.
• Lathe checks may telegraph through to the finished surface of the wood causing less elastic finishes to display fine linear cracks in the surface of the finish film precisely in the same location as the underlying anomaly.

For more detail on some of the suggested cures to many of these issues, or for more information on any other related industry issues, refer to the latest revision of Problems, Causes, and Cures (Technical Publication C200).

Brett Miller is VP of Education & Certification at the National Wood Flooring Association in St. Louis. He can be reached at brett.miller@nwfa.org.