A quick way to get the bottom paint off is to mix some lye or other strong base with some lime and make a past with water. Smear that over the area you want to strip the paint. Let it dry and pressure wash off. If you are doing a small area, "Easy Off" oven cleaner is an expensive source for the same ingredients.... but easier to use and prepare. If you are only stripping the area around the crack... easy off might be the better way to go.