What's the appeal? Imagine moving out of the family room for only 12 hours as a contractor pulls up the old wall-to-wall carpeting, then cuts and assembles prefinished boards. No sanding, no waiting for multiple coats of polyurethane to dry. The floor is complete as soon as the boards are installed.
And these floors can be laid directly over a concrete slab; with solid wood, a grid of 2x4s covered with plywood must first be installed over the slab. This Old House contractor Tom Silva "floats" engineered floors over concrete, gluing the tongue-and-groove joints together, but not fastening the boards to the floor. Some products, designed for floors that won't get wet, snap together and require no glue. Not being fastened down means the assembly can shrink and swell without cracking; a 1/2-inch expansion gap around the perimeter is hidden by baseboards or shoe moulding. When the subfloor is wood, the strips are simply glued or stapled down. Or, "you can float the floor over a 1/8-inch plastic foam insulation pad that's stapled in place," says Silva. "It makes things quieter downstairs."
Not surprisingly, the growth of the engineered-wood-flooring market over the last quarter-century tracked the building boom in the Sun Belt — where houses are built on concrete slabs. The product was invented in Europe shortly after World War II and first imported to the United States during the early 1980s by the Harris-Tarkett company. Popularity has grown steadily, and engineered wood flooring's biggest appeal today is to homeowners who are living in the midst of renovations, since it eliminates on-site sanding and finishing. Remodelers may still have to contend with some fumes, however, because many of the installation glues that manufacturers recommend are urethane-based. This Old House chose engineered floors for the Santa Barbara, Milton, and Watertown projects. "It's absolutely stunning, and it was so easy to install," says Jan Winford, owner of the Santa Barbara home. "Since we were living here during the work, we didn't want to deal with finishing the floors."
Solid wood is available prefinished too, but the surface never winds up as flat as if the wood were sanded after being installed, and then finished. In fact, prefinished engineered floors aren't quite as even as floors that are sanded in place either, says Don Dickel, a third-generation wood-floor installer and finisher in Bangor, Maine. To hide slight irregularities in the surface, manufacturers mill a micro-bevel along each edge-creating 1/32- to 1/16-inch-deep grooves that are a telltale sign of an engineered wood floor.