How to Build an Addition onto a Concrete Driveway

Mark the area for the driveway addition, placing lawn flags in the ground to determine the boundaries.

Clear the marked area of debris and vegetation. Dig up the area for the addition to a depth of 6 inches, starting from the driveway itself and covering the entire area within the boundary. Create a slope to the excavated area away from the foundation of any buildings; the slope should be 1 inch for every 8 feet of slab to be poured for drainage.

Construct a wooden frame for the driveway addition using wooden planks set at the same height as the driveway. Place the frame surrounding the driveway addition area on three sides, using the driveway as the fourth side of the frame. Check the level of the frames using a carpenter's level to ensure that the frames are level with the driveway. Once leveled, secure the frames by nailing the planks at the corners, and then drive wood stakes into the ground outside the frame to hold it stable.

Compact the soil inside the frame using a plate compactor to create a firm foundation for the driveway addition. Plate compactors can be rented from home improvement stores or equipment rental shops.

Pour 2 inches the gravel into the framed area and compact it using the plate compactor. Pour another 2 inches of gravel, compacting that as well.

Place a grid of 1 inch concrete support stones along the bottom of the area atop the gravel, every 5 feet. The support stones are square concrete stones that support the reinforcing rebar grid while the concrete is poured.

Place the steel rebar into the area, with the bars spaced every 2 feet, forming a grid, beginning about 3 inches from the edge of the frame. Tie the crossing bars together using metal ties, twisted at the cross points with pliers.

Mix concrete for your driveway addition in a cement mixer. Use a low slump mix with a compressive strength of at least 4000 psi, as suggested by the Tennessee Ready Concrete Association. Mix the concrete according to the manufacturer's instructions.

Pour the concrete into the excavated boundary, filling the forms. Spread the concrete evenly, using a concrete rake. Level the spread concrete with the top of the forms using a concrete screed. Drag the wooden screed across the two form sides, pushing excess concrete down the slope to fill the form completely. Use a concrete float to smooth the surface of the concrete and then wait 24 hours for the concrete to begin to set.

Use a steel trowel to cut a line between the driveway and the poured addition to create an expansion joint between the two slabs. This joint allows the slabs to expand and contract without causing cracks. Wait an additional 10 days for the concrete to cure.

Remove the forms from concrete addition and then allow it to cure completely for two more weeks. Seal the surface of the addition by spraying it with a layer of concrete sealant. Wait 24 more hours before using the surface.