The previous owner patched, with cement, the corner where the outside wall meets the walkway. The cement floor slab at the edge of the wall had pulled away from the wall and created a gap about an inch if not wider. This is almost the length of the house, 20 feet. The patch is falling apart, did not look like a good job in the first place. In some places it looks like a pretty deep gap. I am worry about water getting in this gap to my basement. How should i repair this problem?