While concrete is durable and long-lasting, there are problems associated with its use. Spalling occurs when the concrete surface is pitted and flaky. This is generally the result of poor installation, especially when too much water is used while mixing. But this can be solved by cutting away the surface and patching the concrete. This process is relatively easy and can be accomplished in a weekend.
Cut away the spalling section. Use a circular saw with a masonry blade to make a 3/8" deep cut around the damaged area.
Use a chisel and hammer to chip away the damaged section that you've cut. Dispose of any debris.
Blend premixed concrete mix with water, according to the manufacturer's instructions. Use a drill with a paddle bit to keep the concrete mixed as you get ready to pour it.
Fill the cut away section of concrete with the patching compiund you've prepared.
Use a 2x4 to smooth the surface of the patched area until it is level with the rest of the surface.
Cover the patched area with a sheet of plastic. Periodically lift the plastic and mist the concrete with water over the next 48 hours so that it dries properly and to prevent future spalling.
Wear proper safety gear, including goggles and a dust mask, when cutting concrete.
If you have a large surface with spalling issues, it may be best to hire a professional to complete the job.