The number of wood products now available for finish flooring has grown dramatically in the last 20 years or so. Earlier, the primary choice was unfinished solid oak flooring, 2-1/4-inches wide and 3/4-inches thick, with tongue-and-groove (T&G) edges. This floor is still very common, but is now just one of a great many domestic and imported wood species.
There are now two major product formats: solid wood flooring and engineered wood flooring. Both formats are available as strips (less than 3-inches wide), planks (greater than 3-inches wide) and parquet tiles. Engineered wood floors are also available in longstrip planks. These floors have their own unique composition and therefore, their own category. The top layer of the long planks is made of individual fillets or slats that are glued together to make up the facing of each plank. Solid wood flooring is available unfinished or prefinished, while engineered wood flooring is generally prefinished.
Because of its plywood-like construction, engineered wood flooring is dimensionally stable, making it particularly suited for use over difficult surfaces such as a concrete slabs below grade. In addition, it is much thinner than solid wood. Engineered flooring may provide an advantage for remodeling projects because it may reduce the need to trim doors and reset adjacent moldings. Use of engineered wood flooring can help remodelers avoid awkward transitions to adjacent flooring surfaces. One of the key tradeoffs in selecting engineered flooring over solid wood, however, is that engineered wood floors can't be refinished as many times as solid wood.
The key specifications for solid wood flooring differ somewhat from engineered wood flooring. However, one comparison that can be applied to both formats is called the Janka Hardness test. This measures the pounds of force it takes to drive a steel ball 1/2 its depth into a particular wood species. The higher the number, the more dent-resistant the wood. The following chart shows how common domestic hardwood species compare to one of the hardest tropical hardwoods:
Red oak is the most common domestic species for solid wood flooring but others include cherry, walnut, maple, beech, birch, pecan, white oak and pine. Some, such as madrone, Douglas Fir and myrtle wood are more common within their natural growth region than outside it and may be more expensive outside it. Over 60 species of imported flooring woods are also available, from Afromosia to Zebrawood.
Most solid wood flooring features T&G edges and is installed by driving fasteners at an angle through the tongue of each board. Square-edge flooring, including parquet, is also available. Square-edged products are typically face nailed or secured with adhesives. Floor boards may also receive a beveled edge; this emphasizes individual boards by creating a shallow V-shaped groove between them.
American producers of solid wood flooring have adopted grading rules to describe minimum specifications for quality and uniformity. Though some grading differences exist between wood species, most hardwood flooring is graded by the appearance of its top surface, based on uniformity of color as well as the presence of knots, surface checks and other imperfections
The cost and appearance of flooring are also affected by how it was sawn from logs during milling. The sawing method determines the relative stability of the wood as well as its figure:
Imported wood flooring is not covered by a uniform set of grading rules. However, domeric and imported wood flooring sometimes carry a designation intended to identify whether or not the wood was harvered using sustainable forerry practices. FSC Certified is one such designation, erablished by the Forer Stewardship Council.
The finish type, method of application and number of finish coats all have a bearing on the durability of wood flooring and its installed cost. With unfinished flooring, site-finishing is a highly variable cost component. Wood can be stained to change its color, mechanically distressed for an antique appearance or subjected to various other treatments. One advantage of on-site finishing is that it makes it possible for the floor to match adjacent trim of the same species. The uppermost layer of finish is a protective layer. It may range from full gloss to semi-gloss to a satin finish.
Engineered Wood Flooring
Engineered floors consist of layers of wood veneer, or sometimes high-density fiberboard (HDF), topped with a single layer of solid wood up to 1/4-inches thick. The top layer is called the wear layer, and it is key to the floor's lifespan. The thicker the wear layer, the more often it can be sanded and refinished before the floor must be replaced. The flooring is often covered by a limited warranty. It may apply only to the finish, or it may apply also to the wear layer and the supporting veneers. Warranties range from three to 25 years.
Engineered wood flooring products are prefinished, often with a tough aluminum-oxide based finish applied under factory conditions in as many as seven or more layers. This eliminates the laborious process of on-site finishing. Finishes range from full-gloss to semi-gloss and satin.
The term overwood refers to a slight height difference in the wear layer that can be felt between adjacent flooring boards. Some manufacturers deal with overwood by machining a micro-bevel along the edges and ends of each board. The bevel makes individual boards more apparent and helps to disguise slight subfloor irregularities. Other manufacturers address overwood with tight manufacturing tolerances and by using only the most stable materials, such as quartersawn wear layers over marine-grade base veneers. Flooring without a micro-bevel looks more like a traditional site-finished wood floor.
Engineered Flooring Installation Methods
Three different installation techniques can be used to install engineered flooring, but not every method is suited to every flooring product. Choosing suitable flooring depends on the type of subfloor and its condition. Each manufacturer specifies the type of installation suitable for its product. Generally, there is little cost differential between the installation methods.
Floating Floor--Each strip of flooring is secured to adjacent strips with a continuous bead of glue; none of the boards are attached to the subfloor. Some products feature a glueless design with a specially shaped edge that allows the floor boards to lock to each other without the need for adhesives. In either case, the resulting floor floats atop a thin sheet of closed-cell foam padding, which acts as a slip sheet to allow the entire floor to expand and contract as a unit. The padding also offers a measure of acoustical insulation and serves as a vapor barrier. Floating floors are particularly suited to installation over concrete.
Nail- or staple-down floor--Each length of flooring is fastened to the subfloor with staples, nails, or special fasteners called cleats. A layer of building felt laid over the subfloor serves as a moisture barrier. Nail-down
Glue-down floor--Each length of flooring is adhered to the subfloor with flooring mastic spread with a notched trowel. The technique is intended for direct application to concrete.