What Is Tongue and Groove Flooring?

Hardwood Floor Installation
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Some unknown genius, many years ago, invented it and we are still using it today.  Even as the range of flooring materials has expanded beyond classic solid hardwood into other areas--laminate, luxury vinyl, and engineered, notably--this ancient technique is still in use today.

What did this genius invent?  A process of joining materials called tongue and groove.  This simple method seams two boards--usually, not not always, floor boards--in a way that holds them together while allowing for some flexibility.

 It's also important to know that traditional tongue and groove has been largely replaced by a similar method for some types of flooring.

Definition:

Tongue and groove is often used in conjunction with wood floor boards, sheet paneling, wainscot, and any number of other materials where a tight, solid seam is required between separate pieces.

Tongue and groove means that each piece has a protruding tongue side and a receiving groove side.

The tongue and the groove each run the entire perimeter of the piece, all four sides.  One tongue fits firmly into the groove of the adjoining board.  The purpose is to control vertical movement between adjoining boards.  Horizontal movement is still allowed to a small degree and, in fact, is a desirable quality, since wood flooring will expand and contract.

Tongue and Groove's Cousin:  Lock and Fold

Basic tongue and groove joinery is a straight tongue that horizontally slides into a straight groove.

To prevent the boards from moving, nails or flooring staples are driven into the tongues.  These fasteners attach directly to the sub-floor.

As laminate flooring manufacturers developed new ways of joining boards, a slightly different technique came about--floating floors.  Floating floors attach only to themselves, from one board to the next, not the sub-floor.

 Luxury vinyl flooring capitalized on laminate's innovations, and in many ways improved on them. 

At first, glue was used to join tongues to grooves.  But an easier method, lock and fold, was developed to allow tongues to fit into grooves with no glue, no fasteners.  

Lock and fold is a method that involves angling one board onto the adjoining board and then folding it downward.  This is significantly different from traditional tongue and groove in that horizontal movement, as well as vertical, is kept in check.  There still is room for some microscopic horizontal movement, but nowhere near the type of movement allowed by classic tongue and groove.  

Advantages

  1. Tight join, requiring minimal amount of nailing or gluing to hold together.
  2. Provides microscopic seams.
  3. With proper coating, tongue and groove can even be water-tight.  This applies to site-finished flooring, not pre-finished.

Disadvantages

  1. Can be difficult to fit the tongue into grooves, especially with boards have become swollen due to humidity.
  2. Tongues can easily break off, unless special care is taken.
  3. Difficult, if not impossible, to disassemble pieces that have been joined with tongue and groove. Tongue and groove wood floors usually cannot be disassembled without significant breakage.