By Brett Miller, NWFA Vice President Technical Standards & Training
According to research conducted in 2018 by the National Wood Flooring Association (NWFA) published in Hardwood Floors magazine (“Today’s Savvy Consumer,” December 2017/January 2018), two-thirds of U.S. consumers want wood floors in their dream homes. With 82 million single-family homes in the U.S. (Statistica, March 15, 2024), that represents a lot of wood floors. For professional flooring contractors, this represents a lot of potential business, especially when it comes to repairing all the existing wood floors already installed. Three such potential repairs include overwood/underwood, uneven bevels and end gaps.
Overwood/Underwood
Identification
Overwood/underwood appears as a vertical offset between two adjoining installed floorboards.
Causes
- Manufacturing Solid and engineered wood flooring tolerances manufactured outside of the applicable industry standards (NWFA/NOFMA, HPVA or similar).
- Intentionally placed in the surface of the floor as an aesthetic design Can be determined with destructive testing or on uninstalled wood flooring boards.
- A characteristic of reclaimed, distressed or sculpted floors.
- Installation-related causes:
- Insufficient subfloor fastener holding power.
- Irregular subflooring.
- Substrate not flat to within required tolerance or contains protruding subflooring fasteners not set prior to installation.
- Deflection in subflooring.
- Debris between boards or subfloor during installation.
- Improper fastener schedule.
- Improper fastener used (wrong length, gauge or type).
- Overdriven/underdriven fasteners resulting from incorrect pressure setting on air compressor.
- Cracked tongues.
- The wrong type of adhesive, trowel or spread rate.
- Improperly installed floating floor.
- Board replacement in which replaced boards were not sanded flat or properly prepared to match elevation of the surrounding floor.
- Installer-manipulated material.
Cures
- When flooring is outside of the industry tolerance or standard, board replacement may be necessary.
- When accompanied by deflection, correct deflection issue before addressing the flooring.
- When flooring installation-related, the affected area may need to be replaced or sanded flat.
- When a characteristic of the flooring material itself, no action may be necessary.
Uneven Bevels
Identification
Uneven bevels can occur within an installed or uninstalled wood floor. They appear as bevels inconsistent in width, depth, shape, profile or size.
Causes
- Flooring milled incorrectly.
- Flooring installed from different product lines, manufacturers or runs.
- Normal and within grade for flooring installed (such as hand scraped, distressed or reclaimed).
- An existing floor with bevels that was resanded and resulted in uneven bevels.
- Installer-manipulated material.
Cures
- Replacement of affected boards when the boards are outside of grading tolerances may be necessary.
- Repair or recreate by hand to match the bevel profile.
- No repair is necessary when the inconsistency is within grade.
- When uneven bevels are the result of a resanded wood floor that contains bevels, the inconsistency may be unavoidable due to site conditions and the sanding process.
End Gaps
Identification
End gaps appear as separations that occur on the ends of two abutting wood floorboards.
Causes
- Loss or gain of moisture in engineered flooring.
- Due to the construction of engineered flooring, each layer shrinks and swells in different directions and at different rates than adjoining It is common for the flooring to shrink or swell in its length when exposed to changes in moisture content.
- Loss of moisture in solid flooring.
- Solid wood generally will shrink or swell only 0.1% to 0.2% of its overall length with changes in moisture content.
- The pith of the tree may shrink or swell at higher rates.
- Flooring not installed tightly together.
- Debris between the boards during installation.
- End joints of flooring manufactured or cut out of square, or mis-milled tongue and groove profile.
- Movement within the subflooring system, and structural or foundation settlement.
- Wood subflooring with excessive moisture during wood floor installation.
- Wood flooring laid perpendicular to direction of wood subfloor Both plywood and OSB generally shrink or swell twice as much in width than in length.
- Nail-down floors:
- Debris between butt-ends of boards during installation.
- Improper subflooring materials that will not hold the fastener.
- Wrong fastener used per flooring manufacturer.
- Glue-down floors:
- Early foot traffic before adhesive has had time to set up during or following installation.
- Improper use of straps or tape used during installation.
- Incorrect adhesive used for flooring being installed.
- Inadequate bond between subfloor and adhesive caused by poor preparation or incompatibility.
- Improper use of adhesive:
- Wrong trowel or spread rate as required by adhesive manufacturer.
- Inadequate adhesive transfer as required by adhesive manufacturer.
- Improper flash time allowing adhesive to skin over.
- Not using a roller when recommended by adhesive manufacturer.
- Floating floors:
- Failure to follow flooring manufacturer’s installation instructions.
- Improper acclimation/conditioning of flooring and the building.
- Moisture or environmentally related issues.
- Inadequate perimeter expansion space at all vertical obstructions. The recommended expansion space may have been adequate at the time of installation and closed due to environmental changes.
- Pinch points caused by door jambs, baseboards, trim or adhesive caulking restricting lateral movement.
- Heavy or fixed-in-place furniture restricting lateral movement.
- Flooring length and/or width exceeding manufacturer’s requirements.
- Lack of, missing or improperly installed transitions.
- Improper or missing glue used on tongue or groove of flooring.
- Improper glue application to tongue or groove.
- Loss of glue bond between the tongue and groove.
- Broken or missing locking mechanism.
- Mechanical lock becomes disengaged. This is most common on end joints with deflection due to a subfloor being out of flat tolerances or improper underlayment material.
- Improper underlayment material used (per flooring manufacturer) below the flooring.
Cures
- Never attempt to repair a floor with moisture issues until all sources of moisture have been located and eliminated.
- Issues with the subfloor must be resolved. This typically is not the responsibility of the flooring contractor.
- For end-gaps caused by a loss of moisture in engineered flooring, restore and maintain humidity levels to normal This may help return the floor to an acceptable appearance.
- Isolation repairs, such as wood filler, color-matched putty or matching wood slivers, may be needed to address aesthetic concerns.
- For square edge material, replace board(s) with longer matching material, then recoat or resand as necessary.
- For beveled edge flooring material, replace board(s) with longer matching material. Additional steps must be accounted for when replicating bevels or edge profiles.
- In the case of widespread end-gaps throughout the floor, removal and replacement of affected areas may be necessary.
The National Wood Flooring Association provides detailed information about overwood/underwood, uneven bevels and end gaps in its Problems, Causes, and Cures technical publication. NWFA’s technical publications are provided to all NWFA members as a member benefit. They are available to nonmembers for purchase. NWFA also provides online training for wood flooring through NWFA University. For more information, visit www.nwfa.org.
