What is the purpose of control joints in tile floors, and what is the typical spacing?

• A. To create non-slip surfaces; spacing every 30 ft.
• B. To decorate the floor; spacing every 2 ft.
• C. To accommodate movement and prevent cracking; spacing around 20–25 ft in large rooms and at changes in plane.
• D. To reduce tile weight; spacing every 50 ft.

Answer: (C)

Control joints are placed to absorb movement in the substrate so tile and grout don’t crack when the floor expands, contracts, or shifts due to temperature changes, shrinkage, or structural movement. By giving the floor intentional break points, you keep cracks from propagating through the tile. That’s why the guidance is to space joints so no area in a large room is more than about 20–25 feet from a joint, and to place joints where the floor changes plane (such as at transitions, changes in direction, or where different substrates meet). The other options miss the purpose entirely—they’re about texture, decoration, or weight, and don’t address movement or proper joint spacing.