How to Add a Concrete Slab Alongside a Driveway

Clear the site for the new slab by digging out the growth and topsoil with a shovel. Dump the soil on a tarp to fill out low areas of the yard. Dig until the site is 12 inches deep, and cut straight down around the sides. Dig the subsoil into a smooth slope away from the existing driveway by removing 1/8 inch more soil with every horizontal foot away from the driveway. Compact the dirt with a vibrating compactor tool.

Drill 1/2-inch holes in the side of the driveway that will meet the new slab with a core drill. Make the holes 6 inches deep across the center of the side. Use a tape measure so they’re spaced 12 inches apart and 6 inches in from either end. Use a wire brush and water to remove any debris from the holes.

Fill the site for the new slab with two 4-inch-thick layers of 3/4-inch aggregate, and compact it.

Use a caulk gun to fill half of each hole with concrete epoxy adhesive.

Insert 12-inch lengths of rebar into each hole to tie the slabs together and transfer weight loads.

Measure the adjoining side of the new site and cut an expansion joint with a utility knife. The joint must be 1/4 to 1/2 inch thick and equal in height to the depth of the new slab. It should be made of semi-flexible material like pressure-treated wood, rubber or foam.

Make slits in the joint from the bottom to the center with the knife, and cut a 1/2-inch holes where each length of rebar will poke through. Press the expansion joint over the rebar so it sits vertically against the adjoining side of the site.

Line the three remaining sides with 2-by-6-inch frame boards, and nail them together at each end with a hammer.

Mix the new concrete in a mixer with the set amount of water, and pour it over the site and 6 inches of exposed rebar pins. Once the wet mix reaches the top of the frame boards, spread the material into corners and sides with a gauge rake.

Even out the surface by pulling a long screed board back and forth over the frame boards from one end to the other. Push a squeegee over any marks created by the boards. After the new concrete sits for about half an hour, use a medium-bristled broom to draw shallow groves in the surface for traction.

Block off the driveway and cover it with moist burlap for seven days so the concrete can cure without drying out too soon.