What is the maximum spacing of the control joints in a slab that is to receive a floor finish?

What is the maximum spacing of the control joints in a slab that is to receive a floor finish?

• A. No control joints are necessary since floor finishes will conceal cracks
• B. Control joints are required every 12 feet
• C. Joints are not necessary
• D. Control joints must be spaced at 8 feet

Answer: (C)

Control joints in concrete slabs are there to control where cracks form as the concrete shrinks and as temperature and moisture change. When a slab will have a floor finish, you want cracks to run along the joints rather than randomly across the surface, because cracks can telegraph through finishes and be difficult to repair. Therefore, for slabs that receive a floor finish, the joints should be spaced so that no panel is wider than about 12 feet in either direction. Spacing joints more closely than 12 feet helps keep cracks narrow and the finished floor smooth. The idea that joints aren’t needed isn’t correct, and placing joints every 8 feet is more conservative than necessary for most cases.

Control joints in concrete slabs are there to control where cracks form as the concrete shrinks and as temperature and moisture change. When a slab will have a floor finish, you want cracks to run along the joints rather than randomly across the surface, because cracks can telegraph through finishes and be difficult to repair. Therefore, for slabs that receive a floor finish, the joints should be spaced so that no panel is wider than about 12 feet in either direction. Spacing joints more closely than 12 feet helps keep cracks narrow and the finished floor smooth. The idea that joints aren’t needed isn’t correct, and placing joints every 8 feet is more conservative than necessary for most cases.