The Purpose of Control Joint Cuts

Cobra Concrete Cutting Services Co. has over 15 years of experience cutting concrete in the Chicagoland area for a variety of large commercial projects. While primarily focusing on serving the Tri-State area, Cobra Concrete is available for service in other states based on requirements.

Our experience gives us the expertise to cut many different types of concrete. We have a team of experts that can plan and cut control joint, to ensure the longevity of your concrete pour.

Control joints are preplanned cuts in concrete that help control where and how cracks appear in poured concrete. Concrete shrinks as it cures and will change in response to temperature. A large area of poured concrete is likely to crack, especially when up against a foundation or street curb.  Placing a control joint into a slab means carefully placing planned cuts into the concrete to allow cracks underneath the surface to be straight and not disturb the surface aesthetics. 

Control joints are generally cut to be about one fourth of the thickness of the slab. Spacing control joints are not as formulated as depth due to factors like slab type, dimensions, and the kind of concrete. A general rule of thumb for spacing is 24 to 30 times the slab thickness. Control joints can be left one of three ways: as is, sealed, or filled. Sealing is done with a flexible material. “Filling” involves filling the entire joint to withstand heavy traffic. Concrete floors that will not have extremely heavy loads can be left as is. Our team of experts can assist in planning, location, and depth of control joints.

Sawing control joints into concrete takes experience. The time window for cutting poured concrete can vary based upon  weather conditions and mix designs. Cutting freshly poured concrete too late can lead to unwanted cracks in the concrete, rendering the joints ineffective. Too early and the concrete will not have cured enough to support the saw and operator. Joints should be sawed as soon as the concrete can withstand the energy of sawing without raveling or dislodging aggregate particles. 

For most concrete work, cutting should take place within the first 6 to 18 hours and never beyond 24 hours. Smaller early-entry saws are available, which may allow cutting to begin within a few hours after placement. When sealing or filling control joints, it is important to wait longer so the joint can widen and any cracks can take place. At Cobra, we use many unique saws for each job depending on the need. Our team will recommend timing and appropriate equipment for precise cutting.

Cutting control joints are not absolutely necessary in every situation. Concrete can be reinforced through different additives and even steel bars located underneath the surface. As other methods are used to keep cracks to a minimum, using control joints is best practice. 

Placing control joints in a slab will help keep cracks from becoming visually noticeable and spreading. In an ideal pour and control joint location, any cracks formed by concrete shrinking will actually occur inside the control joint. When cracking takes place within the joint, it helps control random, ugly cracks that are seen on the top of the surface. Cracks outside of a joint can occur and might be attributed to deficiencies in the concrete mix or curing conditions. Even with minor cracks outside of a joint, you can expect significantly less cracking in a poured slab if control joints are cut with the proper spacing and depth.