How to Attach More Concrete to an Existing Driveway

Excavate the site for the new slab beside the existing driveway with a shovel. Remove 12 inches of top soil and any edging from the area where the two slabs will connect. Compact the soil with a tamping tool until it feels hard.

Line the three sides of the site that won’t connect to the existing driveway with 2-inch by 6-inch frame boards. Screw the boards together at the joints with a drill and two galvanized screws on each end.

Build up the base with two 4-inch thick layers of 3/4-inch aggregate and tamp it between each layer until the rocks wedge firmly together.

Drill a line of holes into the center of the side of the existing concrete, where the slabs will meet. Use a core drill and a 1/2-inch bit and space them 1 foot apart and 6 inches from the ends of the slab. Spray the holes with a hose to flush out any debris.

Use a utility knife to cut a length of foam, rubber or pressure-treated wood expansion joint to fit across the fourth side of the site. The joint must be as deep as the slap will be and 1/4 to 1/2 inches thick. Mark where the holes in the concrete align with the expansion joint and cut a slit from the bottom of the joint to the center where the hole will be.

Use a caulk gun to fill the holes halfway with epoxy.

Drive 12-inch lengths of 1/2-inch rebar into the holes with a sledge hammer.

Fit the cut expansion joint over the rebar and paint the exposed rebar with steel primer and a paint brush.

Empty concrete mix into a mixer with the prescribed dose of water and mix it until it is thick. Pour the concrete over the exposed rebar pins and the rest of the site.

Drag a long screed board across the frame boards from one end of the site to another, pushing any excess into low areas so the new slab is level. Smooth any marks created by the board with a squeegee.