How to Repair & Replace Spalled Concrete Expansion Joints

Use a chisel and hammer to break away any concrete chips from the spalled surface, placing the tip of the chisel onto the base of the chip where it meets the concrete and then hitting the head of the chisel with the hammer to break it off.

Remove any material contained in the expansion joint, such as foam or cork, from the joint with a small pry bar. Brush any loose debris from the expansion joint with a nylon brush. Sweep away all debris with a stiff-bristle broom.

Scrub the damaged area clean with a pH-neutral cleaner and a scrub brush. Rinse off the concrete with a hose and then allow it to dry for about two hours.

Measure the depth and length of the expansion joint with the tape measure. Fill the expansion joint with a piece of cardboard, extending 2 inches above the surface of the joint, in order to protect the joint from the concrete repair patch material.

Brush the spalled area of the concrete with an acrylic bonding agent. Use a paintbrush to apply the agent to the concrete evenly, extending the coverage to a point about 2 inches from the edges of the spalled area. Let the agent dry to a tacky state, losing the wet look but continuing to feel sticky when you touch it with the tip of a finger.

Mix the concrete patch material in a small bucket using a drill and a grout mixing bit, following the manufacturer instructions for the amount of water to add.

Spread the patch material over the spalled section with a trowel, feathering out the edges 1 to 2 inches beyond the spalled portion. The cardboard will prevent you from getting the patch into the joint, so spread it up to the cardboard edge. Smooth the patch with the trowel as you go along. Allow the patch material to cure overnight.

Pull the cardboard from the expansion joint.

Subtract 1/2 inch from the joint depth measurement, and buy foam backer rod that’s the same diameter as the adjusted measurement and slightly longer than the expansion joint. If you cannot find a single rod long enough, get several lengths that equal the needed length when butted against one another.

Cut the rod to fit, and then put the rod into the joint, pressing it to the bottom of the joint with a putty knife.

Place strips of masking tape along the edges of the joint on the repaired concrete. Fill the 1/2 inch of remaining expansion joint space above the rod with elastomeric sealant. Use the trowel to press the sealant into place, filling the joint to the surface level of the concrete.

Remove the masking tape to cut the edges of the sealant into a sharp line along the joint edges. Wait 48 hours for the sealant and the patch material to cure further before walking over the repaired area.