By Brett Miller, NWFA Vice President Technical Standards, Training & Certification
In a nationwide conducted by NWFA of U.S. consumers, real wood was identified as the top aspirational flooring preference among homeowners. Respondents cited durability, maintenance, healthy homes, and long-term value as among their reasons for choosing real wood floors, but the top reason remains the product’s appearance. While the various species, colors, and grain options make real wood floors the most-imitated flooring alternative, wood offers a visual aesthetic that cannot be truly duplicated with other flooring materials.
The installer is responsible for ensuring the highly prized appearance of real wood floors remains the main focus of the installation. There are, however, several installation issues that can make that goal more difficult. They include compression set, panelization, sidebonding, telegraphing fasteners, crooked installations, and telegraphing substrates.
Compression set is a generally uniform appearance of gaps between wood floor boards that coincides with the narrowing/crushing of individual board edges. The appearance of compression set may be similar to gaps from other causes, but when the floors are at the same moisture content at which they were milled, compression-set boards will be narrower than the milled width and may exhibit slightly raised edges.
The cause of compression set generally is exposure to substantial moisture causing excessive expansion, resulting in damage to board edges. Once the boards are brought into an environment with lower moisture, the subsequent contraction will affect boards. Once the wood fibers have been damaged they may be unable to regain their original dimensions. The compression can become exaggerated by debris becoming embedded in the gaps between boards. In addition, filling seasonal gaps during the dry season can cause compression set when the floor expands again during the more humid months.
To repair compression set, the sources of moisture first must be removed. It may be possible to make isolation repairs using wood filler, color-matched putty, or matching wood slivers to address aesthetic concerns. In the case of widespread gaps throughout the floor, removal and replacement of affected areas may be necessary.
Panelization is a generally uniform appearance of gaps or peaks in the surfaces of the wood floor that directly coincides with movement in the subfloor material beneath it. It can be caused by moisture or acclimation issues, such as the moisture content of the wood floor not being aligned with the subfloor at the time of installation, or excessive moisture present in the wood subflooring during wood floor installation, which is then lost and results in gaps between boards at the subfloor seams. These types of gaps typically are most noticeable at approximate intervals that coincide with the subfloor panel widths.
Other causes can include hot spots in the subfloor, such as poorly insulated heating ducts, hot water plumbing lines, radiant heating systems, register openings, and appliance motors. These can result in subfloor movement or shrinkage after the floor is installed. These types of gaps may or may not align with subfloor joints.
Other causes can include movement within the subflooring system due to structural or foundation settlement; wood flooring installed parallel to solid board subfloor planks or an existing wood floor; or skipped, inconsistent, or improper application of adhesive during full-spread adhesive application that will likely result in uneven movement of the flooring system.
Similar to issues with compression set, to repair panelization any sources of moisture first must be removed. It may be possible to make isolation repairs using wood filler, color-matched putty, or matching wood slivers to address aesthetic concerns. In the case of widespread gaps throughout the floor, removal and replacement of affected areas may be necessary. When flooring has been installed parallel to solid board subfloors or existing wood floors, the wood floor likely will need to be removed. Note: the structural integrity of the subfloor system generally is not the responsibility of a wood flooring installer unless he/she installed the subfloor system. In most situations, structural-related issues should be addressed by a qualified professional.
Sidebonding is a condition where localized gaps develop between flooring boards, while adjacent groupings of boards remain tightly bonded together with no apparent separations. These gaps sometimes will exhibit wood fractures along the gap as a result of the finish bond tearing away small pieces of wood from the adjoining plank.
A common cause of sidebonding occurs when the edges of individual boards have become adhered to one another, which is followed by shrinkage of the boards due to a loss of moisture. In some cases, board bonding occurs when finish (most commonly water-based) seeps between the boards, dries, and forms a permanent bond between boards. The same can happen with glue.
To repair sidebonding, it may be possible to make isolation repairs using wood filler, color-matched putty, or matching wood slivers to address aesthetic concerns.
Telegraphing fasteners appear as dimples or bumps along the nailing surface of the finished flooring. They are related to fastener location and/or installation method. Some common causes include using the wrong gauge fastener, underdriving/overdriving fasteners, improper placement or angle of the flooring nailer, using engineered flooring with thin veneers, and debris embedded within the tongue and groove. To repair telegraphing fasteners issues, the affected boards must be replaced.
A crooked installation is a wood floor appearing bowed or out-of-square. No wood floor installation will be perfectly straight, but when the straightness takes away from the overall appearance, an aesthetic remedy may be necessary.
A common cause of crooked installations includes the structure, or elements within the structure, being out-of-square, which is beyond the control of the installer. Another cause could be that the flooring drifted out of singular-line-plane during installation. This could happen with premature foot traffic on glue-down installations, debris between floor boards, or improperly milled material.
Repairs to crooked floors may not be possible if the structure is out-of-square. Tapering boards during installation may make crooked installations less noticeable. After installation, if the problem persists, replacement may be necessary.
A telegraphing substrate will result in the flooring looking uneven, wavy, or out of flatness. Wood floors may be installed over out-of-level subfloors, but should fall within NWFA floor flatness tolerances. For installations using mechanical fasteners of 1 1/2” and longer, the subfloor should be flat to within 3/16” in 6’, or 1/4” in 10’, unless otherwise specified by the wood flooring manufacturer. For glue-down installations, floating installations, and installations using mechanical fasteners of less than 1 1/2”, the subfloor should be flat to within 1/8” in 6’, or 3/16” in 10’, unless otherwise specified by the wood flooring manufacturer.
It is the responsibility of the flooring installer to assess substrate flatness prior to installation. Gradual variations in subfloor flatness may not affect the wood flooring performance, but may be considered unacceptable when overwood, vertical movement, slight gapping, squeaking, or noisy floors result.
Common causes of telegraphing substrates include flooring installed over abrupt variations in elevation/flatness of the subfloor system or screeds; improperly installed or inadequate subfloors or subfloor systems; improper joist spacing/panel thickness combination; structural conditions; movement or cracking within an existing concrete slab subfloor; or flooring installed over improperly applied compounds, improperly installed underlayment materials, or uneven screeds.
Repairs to telegraphing substrates require removal of the floors to repair the substrate. Correcting uneven concrete substrates may require grinding high spots and/or filling low spots with self-levelers and patches. Remediating uneven wood substrates may require sanding, use of shims, or other approved materials. Any repairs needed for structural subfloor-related issues, such as joists, should be addressed by a qualified professional.
Detailed information about installation appearance problems, their causes, and their repair, is available in the NWFA’s Technical Publication No. C200, Problems, Causes, and Cures. All NWFA technical publications are available for free to NWFA members. More information is available at nwfa.org/technical-guidelines.