Why Is It Necessary to Have a Gap Between the Concrete in the Sidewalk?

Function

• The gaps, or control joints, created every few feet across the width of sidewalks are planned cracks. Most concrete slabs will eventually crack anyway as temperatures drop and the material shrinks. Cutting evenly spaced, straight control joints gives the slab flexibility to shift as needed, preventing jagged cracks from forming.

DIY Control Joints

• If the sidewalk is poured on a hot day, control joints must be cut within 6 to 12 hours of the pour. The depth of the cut should be equal to a quarter of the depth of the slab. For instance, a 5-inch-thick sidewalk should have gaps 1 1/4 inches deep. For sidewalks, the space between each gap should be 4 feet. Do-it-yourselfers can cut the joints with a masonry saw once the surface feels hard to the touch.

Risks

• Adding the control joints is a necessary step in the installation process that may be tempting to skip, especially if you’re exhausted. Neglecting to cut the joints will increase future maintenance. Patching deep, jagged cracks takes time and it’s difficult to blend the patch into the rest of the surface. If the foundation is not deep enough, the sidewalk will also be more vulnerable to deep cracks caused by frost heaves.

Maintenance

• Once the control joints are cut and the concrete has cured for about a week, you must seal the surface with exterior penetrating sealant. In addition to strengthening the porous slab, sealant repels water from the surface, protecting the foundation beneath. Plan to reseal the sidewalk every few years as it wears away with foot traffic and weather.