Tongue and groove moulding involves the use of two pieces of similar wood with interlocking components. Each slat of wood has two sides. One is a tongue — a thin deep ridge — and the other is the groove, which is a slot cut along the edge. The tongue of one slat fits neatly into the groove of the other, creating a sort of locking connection that does not require glue. In fact, adhesives are ill-advised because shrinkage in the wood could pull the seam apart. The use of the tongue and groove method was mainstream until the invention of plywood and other substrates that allowed the builder to cover large portions of the structure with a solid piece of durable wood. Today cabinets, hardwood flooring, and moulding are still using the tongue and groove method for installation, as it provides for the use of beautiful wood slats and a flawless seam.
The most common type of tongue and groove is the square slot and rounded tongue. However, there are other design methods that are employed when the situation calls for them. For instance, dovetailing is one method of tongue and groove that is still frequently used in upscale cabinet making. The dovetail and groove allow for a very tight, non-slip fit that provides a durable, long lasting design when making cabinets.
Moulding still uses tongue and groove in the initial production phase. Most moulding is made up of end cuts, or pieces of wood that are left over from the initial cutting stage in the saw mill. Moulding comes in a variety of shapes and lengths and often has to be produced using the tongue and groove method in order to obtain lengths that are longer than eight feet. Another reason why tongue and groove is used so regularly in the production of moulding is because lengths that are over eight feet have a tendency to warp, due to its likelihood to shrink as it dries. When moulding is made up of shorter pieces of wood, the shrinkage and warp is virtually negated. The product can then be sold to the end user and installed along walls and doorways without warping and shrinkage.
Today, tongue and groove moulding is also used for paneled walls or ceilings. Fitting together snuggly, the individual pieces of hardwood can come together to provide a truly beautiful and unique sort of backdrop or focal point in a room. Again, the use of shorter pieces allows for added stability and prevents any warping and shrinkage, so the beauty lasts for years to come.