Tongue and groove flooring was an innovation of the 17th century. Much like dovetail joints, the tongue and groove allowed craftsmen to attach parts of a whole together without the use of nails. The process is still used today. Planks of hardwood are snapped together to create beautiful flooring, the seams barely discernible. Though not every hardwood floor is made from planks manufactured with tongue and groove, it is, and most likely will continue to be, the predominant form of flooring found in homes around the world.
Until the 17th century, floors were tamped down dirt, compressed to a hard finish. Any wood used was confined to the practical; rough squares were used beneath beds, chairs and tables for stability. Even these were usually covered with thick carpet. The only places wood planks were used to create a full floor were in haylofts converted to sleeping quarters.
In the later 17th century, though, hardwood floors came to be all the rage with the European aristocracy. The planks were wide, up to 7 inches, and often planed to create patterns or parquetry. These floors were the first to employ the tongue and groove configuration. In America, where timber was readily available and so costs were considerably lower than those in Europe, hardwood floors were becoming commonplace. By the 19th century, tongue and groove flooring was found in the majority of upper and middle class homes.
Tongue and groove flooring can be constructed from many kinds of woods. The more popular woods used are oak, maple, Brazilian cherry and bamboo. The wood is planed into planks measuring from 3 inches wide up to 5 inches wide. With tongue and groove flooring, each plank fits into the next. One side is the tongue, a rounded protrusion running the length of the plank. Along the other side is the groove in which the tongue is fitted.
Tongue and groove flooring can be solid wood or engineered. Solid wood flooring is constructed as a solid piece of wood. Engineered wood is layered. A soft wood is attached to a hardwood and is then sandwiched between the hardwood and a plywood base. The plywood base is resistant to moisture and provides stability. The softwood creates a buffer zone.
Both solid and engineered wood flooring are installed using the tongue and groove method. Solid wood, however, is still often glued or nailed down as well. Engineered flooring can be floated. This means the tongue and groove is used to snap the planks into place and the floor is neither nailed nor glued to the subfloor. In recent years, however, manufacturers are producing solid wood floors that need not be anchored to the subfloor.
Tongue and groove flooring allows the planks to fit closely together, creating a smooth finish and more secure seams. Solid wood tongue and groove flooring can have a very long lifespan; it can be sanded down and refinished. This isn't true for engineered wood, as the hardwood veneer is too thin to allow for subsequent sandings. Though it may not have quite the lifespan of solid wood, engineered wood is easier to install.