Sweep away loose concrete and debris from the damaged corner.
Create an L-shaped wood form from 1-by-6-inch boards. Align one board's end to the end edge of the second board and secure it with 2-inch nails.
Spray the L-shape form’s interior with cooking spray. This prevents the concrete from sticking to the form.
Apply latex bonding liquid to the step’s damaged corner. This helps the concrete adhere to the old step
Align the L-shape form’s top edge to the stair’s corner edge and tape in place with duct tape. Secure it flush to the stair’s front and side edges. Use several pieces duct tape holding it in place.
Mix quick-drying concrete in a small bucket, according to the manufacturer's directions, and pour in the corner area. Pour it into the L-shape form to the top and smooth with it a small trowel. Let it dry 24 hours.
Sweep away any dirt, debris or loose concrete from the cracked area. Be sure the area is dry.
Mix quick-drying concrete according to the manufacturer's direction in a small bucket with a pouring lip.
Pour a very small amount of the new concrete into the crack and smooth it with a small trowel. Spread the concrete to blend into the surrounding concrete. Let it dry for 12 hours.
Seal the freshly filled crack with an epoxy concrete sealer.
Sweep the concrete clean of dirt and debris. Clean off any grease or grime with a small amount of dishwashing detergent. Rinse the concrete and let it completely dry.
Apply concrete sealer with a large paintbrush. Be sure it gets into the corners. Let the sealer dry for the manufacturer's recommended time.
Prime the area with exterior latex primer. The primer used on top of the sealant prevents the cement from absorbing the last layer of paint. Let the sealer dry for at least eight hours.
Apply a top coat of exterior latex paint. A second coat may be required to achieve the desired color. Let the final coat dry for at least 12 hours.