Which statement best describes the primary purpose of control joints and their typical spacing in large rooms?

• A. To accommodate movement and prevent cracking; commonly around 20–25 ft in large rooms and at changes in plane.
• B. To reduce tile weight; spacing every 2 ft.
• C. For decorative effect; spacing every 5 ft.
• D. To trap water; spacing every 15 ft.

Answer: (B)

Control joints are placed to accommodate movement in the tile system, stemming from substrate expansion and contraction, drying shrinkage, and other stresses. By giving a deliberate place for that movement, they prevent cracks from propagating through the tile and grout. In large rooms, the joints are typically spaced about 20 to 25 feet apart and are placed at changes in plane (such as where the layout changes direction or the floor meets walls). This spacing provides the tile system with enough flex to move without cracking.

They’re not about reducing tile weight, spacing every 2 feet would be excessive and impractical, they’re not decorative, and they’re not intended to trap water.