How to Lay Concrete With Key Breaks

Prepare and plan for the control joints after the gravel or other base material has been prepared, and the forms have been installed. The joints must be placed at equally spaced intervals. For sidewalks, space joints every 4 to 6 feet. A rule of thumb for larger slabs is to use the thickness of the slab to determine how far apart the control joints should be. You can do this my taking the thickness in inches and doubling or tripling that figure to determine how far apart in feet the control joints should be. So, if the thickness of your slab is 4 inches, your control joints should be 8 to 12 feet apart. Also factor in the width of the slab. If a slab is 14 feet wide, 7-foot sections might look best.

Mark on the forms where your control joints will go.

Pour the concrete, using a screed board or 2-by-4 to level the surface of the concrete, and run a float over the surface. Let the concrete sit for a few hours before attempting to create the grooves, as it must have a consistency that allows the slab to retain the joints.

Run an edger along the concrete forms, around the perimeter of the pour.

Place guides for the control joints. For a relatively narrow slab like a sidewalk, simply lay a 1-by-4 across the slab. For a larger project, put wooden stakes opposite each other outside the forms, and stretch a string between them.

Create joints, using a jointing tool or groover. The groove must go down at least one-fourth of the depth of the slab. If you're working on a sidewalk, you can make the groove easily while kneeling or standing on either side. For a larger slab, use a thin board or panel insulation as a kneeling board to redistribute your weight. This will allow you to create the groove without harming the concrete finish.

Cut into the bottom of each groove, penetrating through the slab every few inches, using a pointed trowel.

Run the jointing tool or groover over the control joints again to smooth any rough edges created by the trowel.