Gluing Down Solids - Can I really glue down 3⁄4-inch solid wood flooring?
Bob Sweezey, technical director at Memphis, Tenn.-based adhesive manufacturer Stauf-USA, answers:
Solid products have been glued down overseas for many years and have also been successfully installed throughout the United States. A solid product from 5/16 to 3/4 inch thick can be glued within the following parameters:
- Both the flooring manufacturer and the adhesive manufacturer must recommend their products for glue-down installation of solid wood flooring. Check with the wood flooring manufacturer for which adhesive is recommended; I recommend only adhesives with zero water (polymer or moisture-cured urethane adhesives). The proper notched trowel must be used.
- The installation must be installed ongrade or above-grade.
- The concrete subfloor must measure under 3 pounds of moisture per 24 hours per 1,000 square feet when using a calcium-chloride test.
- The concrete must be free of sealers and contamination (dust, paint, adhesive residues, etc.).
- The concrete must be flattened (as needed) to within 3/16 inch per 10 feet, grinding it down in high spots and using a leveling compound of 3,500 psi for low spots.
- As with any installation, humidity and temperature must be controlled using a humidifer, dehumidifer or both to prevent excessive expansion and contraction. The acceptable range is between 35 to 65 percent relative humidity and 60 to 80 degrees Fahrenheit.
- The wood flooring must be straightline ripped to ensure absence of crooks (where the ends touch the adjoining board and the middle does not, or the middle touches the adjoining board and the ends do not). Crooks can usually be corrected in a nail-down installation, but will never be held by glue.
- Bowed boards (lifted in the middle or on the ends) can be remedied by adding weight (i.e., boxes of wood yet to be installed). Glue will not reach up and grab a bowed board—installers must ensure contact. Failure to make contact with the adhesive results in hollow spots, and this in no way is a glue failure. As with any glue-down installation, clean-up with the appropriate adhesive cleaning agent is the professional way to complete your installation.