What Is Tongue and Groove Flooring?

Hardwood Floor Installation
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A process of joining materials called tongue and groove has been around for many years. This simple method seams two boards—usually, but not always, floorboards—in a way that holds them together while allowing for some flexibility. 

What Is Tongue and Groove Flooring? 

Tongue and groove are often used in conjunction with wood floorboards, 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 floorboard piece has a protruding tongue side and a receiving groove side. The tongue and the groove each run the entire perimeter of the piece, on 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.

Fun Fact

With the invention of the side matcher, a machine that turns wooden planks into floorboards, the first hardwood tongue and groove flooring was created in 1885.

Advantages

  1. Tongue and groove floors feature microscopic seams, requiring a minimal amount of nailing or gluing to hold the boards together.
  2. With proper coating, tongue and groove can even be water-tight. This applies to site-finished flooring, not pre-finished.

Disadvantages

  1. It can be difficult to fit the tongue into grooves, especially with boards that have become swollen due to humidity.
  2. The tongues can easily break off unless special care is taken.
  3. It's difficult, if not impossible, to disassemble floorboards that have been joined with tongue and groove. Tongue and groove wood floors usually cannot be taken apart without significant breakage.

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 the tongues to fit into the grooves without glue or fasteners. 

Lock and fold 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's still room for some microscopic horizontal movement, but nowhere near the type of movement allowed by classic tongue and groove.