Concrete porches may begin to crack where they meet the house. This is caused by the phenomenon of "settling," in which the home's foundation actually sinks into the ground over a period of many years. With this shift occurring, the concrete porch will start to visibly separate from the residential structure. To fix this problem, you only need to bridge the gap, using newly mixed concrete. While this may seem like a task only a contractor can do, you can do it yourself with a few common masonry tools and materials.
Clean out the separated area between the house and the concrete porch using a shop vacuum to remove all debris.
Place a wheelbarrow near the separation and combine one part cement with three parts masonry sand, then dampen with a hose.
Stir up the cement and sand with a masonry hoe, adding more water as necessary. The mixture should become a mud-type consistency.
Open a can of concrete bonding agent and pour it directly into the separation between the porch and the home.
Tip the wheelbarrow up, allowing the concrete to pour into the gap. Fill the gap completely, then smooth it with a trowel. Scrape up excess concrete as necessary, smooth again, then let dry for 24 hours.
Apply a coat of concrete sealant to the patch using a paintbrush once the concrete has completely dried. Let the sealer dry for another 24 hours to finish the repair.