For hardwood installations over a wood subfloor, one of the biggest concerns I see with the wider engineered planks being sold and installed is squeaks and creaks. The majority of installations I’m being called out to inspect have improper fastening and no adhesive assist to minimize the movement of the plank. Additionally, both sales associates and installers need to make sure to read the warranties from manufacturers—many of them will not warranty their product in a nail-/staple-down installation over Oriented Strand Board (OSB).
So, what’s the biggest issue I’m seeing when I get called out to inspect? Improper fastening. Since planks are getting wider, they need more fasteners to stay in place. While the National Wood Flooring Association (NWFA) has its own written guidelines, remember that manufacturer guidelines always supersede industry guidelines—so read the manufacturer guidelines!
NWFA guidelines state: “Top-nail and blind-nail the first row (hand-nail if necessary), using appropriate fasteners. Denser species may require pre-drilling. Each succeeding row should be blind-nailed wherever possible.
“a. Typical: Narrow crowned (under 3/8 in.) 1 to 1 1/2-in. staples or 1 to 1 1/4-in. hardwood flooring cleats designed for engineered flooring, spaced as recommended by the manufacturer.
“b. Typical: Every 3 to 4 in. with staples, every 4 to 6 in. with cleats, and within 1 to 2 in. of end joints. Use appropriate sized fastener for top nailing first row, last row and any area where blind nailer will not fit.”
(Photo 1 shows the method of using rare earth magnets to identify the fasteners and fastening schedule.)
Another concern I’m seeing is installers using a tube of subfloor adhesive for the glue assist method. These types of adhesives are not recommended for hardwood flooring. Many wood flooring adhesive manufacturers offer the proper adhesives, which will not crystallize and allow the wood flooring to expand and contract without losing bond.
So, do you full spread or run a serpentine along the subfloor? This will depend on whether there are any manufacturer guidelines for glue assist. If the manufacturer doesn’t have any recommendations, here is what you can think about:
Full spread with a smaller notched trowel, as you are using the adhesive as an assist and not the primary fastening system. If using a tube/sausage tube type of adhesive, make sure the serpentine line you are applying to the subfloor spans the full width of the plank; running a small serpentine only down the middle of the plank can create a problem. Once the adhesive sets, you’ll end up with a teeter-totter effect which allows movement of the plank. What you thought would work to minimize squeaks/creaks has actually enhanced the potential for movement!
Here are NWFA’s installation guidelines in reference to glue assist: “If adhesive is used with nailing, follow wood and/or adhesive manufacturer’s instructions for installing plank flooring.”
The NWFA does not have a set guideline when it comes to nail/staple with a glue assist, in regards to what width of board requires this method or if a full spread/serpentine bead is recommended. From personal experience, I’ll say that many installers in the industry will utilize the fastener and adhesive method when a plank is 5 in. or wider.
So, how do you make corrections? If an asphalt-saturated vapor retarder has been installed, trying to make any corrections is difficult (Photo 2). You’ll have installers using an 18-gauge finish nailer and face nailing, which can be unsightly and doesn’t allow for the injection of adhesive since the vapor retarder will not allow a bond. Photo 3 shows an attempt at corrective work where an underlayment was installed under a nail-down installation. The installer attempted to repair it with adhesive, but only ran a bead down the center. When the adhesive cured, it allowed vertical movement of the plank.
Flatness concerns are an issue with both wood subfloors as well as a direct gluedown over concrete. This is another concern I see on inspections. The NWFA guidelines are: “Wood subfloors must be flat, clean, dry, structurally sound, free of squeaks and free of protruding fasteners.
“1. For installations using mechanical fasteners of 1 1/2 in. and longer, the subfloor should be flat to within 1/4 in. in 10 ft. or 3/16 in. in 6 ft. radius.
“2. For glue-down installations and installations using mechanical fasteners of less than 1 1/2 in., the subfloor should be flat to within 3/16 in. in 10 ft. or 1/8 in. in 6 ft. radius.”
Should factory-finished flooring run parallel or perpendicular to the joists? If you read the installation guidelines from manufacturers, very few address will this. The NWFA does not currently have a guideline for running engineered wood floors perpendicular to the joists.
However, for solid strip and plank, NWFA guidelines state: “Unfinished and factory-finished solid strip and solid plank flooring should be installed perpendicular to the joists or on a diagonal for any single layer subfloor. (Exception: Over diagonal, solid subfloor boards, install perpendicular to joists or subfloor direction.)”
My recommendation is to run factory-finished engineered the same as any solid strip or plank—but once again, if a manufacturer has their own recommendations, be sure to follow them.