Your home's foundation is constantly under stress from different forces. It bears the weight of your home and the people and objects inside it, the ground shifting beneath it and constant exposure to moisture and temperature changes. When cracks appear in the foundation wall, it's best to patch them immediately. Water can seep through the cracks, leading to water damage, and if it freezes while inside the crack it can make the crack larger. Over time, small cracks can create major problems with your foundation.
Chip at the crack with a hammer and chisel to make it slightly larger. Tap the chisel about a 1/4-inch beneath the crack, and work the chisel at an angle to make the crack wider at the bottom of the crack than on the surface.
Clean all dust and debris from the crack with a stiff wire brush and shop-vac.
Mix a batch of patching mortar, following the instructions on the packaging.
Fill the crack completely by adding mortar with a putty knife. Smooth the surface of the patch with the putty knife. Allow the mortar to set for the time specified on the packaging.
Brush the surface of the patch with a wire brush. This helps the patch blend into the foundation.