Tongue and groove

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Tongue and groove (sometimes T&G) is a method of fitting similar objects together, edge to edge, used mainly with wood: flooring, parquetry, panelling, etc. Before plywood became more common, tongue and groove boards were also used for sheathing buildings and to construct concrete formwork.

Each piece has a slot (the groove) cut all along one edge, and a thin, deep ridge (the tongue) on the opposite edge. The tongue projects a little less than the groove is deep. Two or more pieces thus fit together closely. Such a joint should not be glued as shrinkage would pull the tongue off. The tongue and groove could be cut in a number of ways.

• Most was done in large quantities using a spindle moulder.
• It can be done using a circular saw bench.
• Small lengths can be cut using suitable planes: a plough for the groove and a tongue plane for the tongue. Alternatively, in the later years of hand tools, a combination plane was available. This small-quantity work would be done today with a spindle router.

For most uses, tongue and groove boards were rendered obsolete by the introduction of plywood and later composite wood boards but it is still used in good-quality flooring and plywood can be tongued all round to fit it flush into a framed structure. As well, plywood for sub-floors used in platform framing is often supplied with tongue and groove edges.