 because you've got to have something to bond it to the existing concrete. That might be a little bit easier to apply since it's a vertical surface. The Quikrete people also have one called Zip-It Mortar. It's three pounds of a powder, has a bonding agent in it, and it's designed for overhead concrete patches and vertical patches. But I think I'd try the anchoring cement first, just based on the thickness that you're going to need.