What kind of subfloor should be used for engineered hardwood flooring?
Engineered hardwood flooring is versatile and could be installed on different subfloors. Many of engineered hardwood floors are manufactured with three or five-ply. This helps the engineered floor to perform better than solid wood in presence of moisture, making it a better choice in places such as humid regions, that usually are less than ideal for solid wood.
Engineered wood can be installed in many ways such as using glue on a concrete subfloor, or float and or nail or staple with wood subfloor, and. It goes down easily over concrete, plywood, OSB and underlayment-grade particle board. Or, you can install it on top of existing hard surface floor coverings, such as vinyl, terrazzo, ceramic, cork or existing wood flooring. Engineered wood also can be used on grade or above or below grade (basement).
Some engineered floors can also be installed over heated floor.
Concrete. The mix must be structurally sound (at least 90 to 100 pounds) when gluing down wood flooring. Some manufacturers recommend a topical sealer/bonding agent that allows for installation of glue-down engineered wood over lightweight concrete. You can install floating engineered flooring over lightweight concrete. The concrete must have cured for at least 60 days and must be dry. When using a calcium-chloride test, results should be 3 pounds or less. If using a moisture meter, refer to the flooring manufacturer’s guidelines for acceptable meters and readings.
The prep work for laying engineered hardwood flooring varies depending on what’s under it, but any subfloor needs to be flat (within 3/16 inch in a 10-foot radius, or 1/8inch in a 6-foot radius); structurally sound and clean; and free of dirt, paint, drywall patch and other contaminates. Below are some common subfloors and—generally speaking—the kind of prep usually done for each. (Always check with your flooring manufacturer for specific guidelines.)
Plywood. It must have a minimum 5/8-inch thickness. For square-edge plywood, 3/4-inch is required,usually CDX grade or smoother.
OSB. This must be 3/4-inch tongue-and-groove, APA rated, underlayment-grade OSB. Check with the flooring manufacturer about using OSB. The wax side must be down for glue-down flooring applications.
Particle board. This must be APA-rated performance standard and stamped underlayment grade, 40-pound minimum. Flooring should be glued—not stapled or nailed—but can be floated.
When considering your subfloor, also think about the joists. The industry standard for hardwood floors over joists is 16 inches o.c. and for floor truss systems, it’s 19.2 inches o.c. Consult the manufacturer, NWFA or NOFMA recommendations if joists/trusses are at a wider distance than recommended. This is not to say that you cannot install over a wider width,but the performance of the flooring may suffer due to interior deflection in the subfloor. You may avoid this by adding subfloor material to increase it to a minimum total thickness of 1 1/8 inch.
Vinyl or VCT. These coverings must be firmly adhered and bonded to the subfloor beneath, perimeter glued vinyl must be removed if the new flooring will be nailed, stapled or glued down. Any waxes or topical coatings must be removed. It’s also a good idea to lightly sand to achieve a good mechanical bond. Remember, any vinyl flooring manufactured prior to 1990 could contain asbestos. In that case, do not sand it. Consult the proper authorities or agency for regulations and proper procedures for asbestos abatement.
Marble, terrazzo, ceramic tile. If you are not floating your floor over these types of floor then you must sand with at least 20-grit open coat sandpaper prior to gluing down wood flooring. This will help achieve a proper bond to the existing floor or flooring.
Existing wood floors (on- or above-grade only). Old finish and high spots must be sanded off; any loose planks should be nailed down. The new floor must be laid at a 90-degree angle to the old flooring. If that can’t be done, 3/8-inch or 1/2-inch plywood can be installed on top of the old flooring, leaving a minimum 1/8-inch gap between each plywood panel to accommodate expansion from heat and moisture, and the new flooring can be laid in any direction.
Cork underlayment. Most engineered flooring can be glued down or floated over properly installed cork underlayment (used for sound absorption). Refer to the manufacturer’s guidelines on installing the cork and wait three to five days before installing the wood flooring. This allows the adhesive bonding the cork to the subfloor to cure properly.
Radiant-heated subfloors. Some manufacturers allow for floating or glue down floors over radiant-heated subfloors, check with flooring manufacturer’s recommendations. The industry guidelines can be found on the NOFMA or NWFA Web sites or in the manufacturer’s installation manual.