Foundation corner cracks are extremely common in residential concrete foundation slabs. These cracks are also commonly referred to as slab cracks. They occur, as the name suggests, at the corner of the foundation where brick veneer is installed on the house. That’s right, they only occur along walls that have brick veneer on the outside of the house.
Characteristics of a foundation crack include a “wedge” shaped crack in the concrete often including a slight displacement or shift in the concrete wedge. The crack usually starts 3 to 8 inches from the corner of the concrete and is located on both sides or faces of the foundation.
So, what causes a foundation crack?
The answer is two fold. First, there is a minor construction detail issue where the base flashing (black plastic in the photo below) in the wall assembly is not properly installed over the concrete exposing the top of the concrete foundation. Then brick and mortar is installed directly onto the concrete slab creating a bond between the brick and mortar (brick veneer) and the concrete foundation. Secondly, mother nature gets involved when the bricks in the brick veneer are heated by the sun causing them to expand. That’s right, the brick stretches when heated and causes the bonded brick and mortar, where the black plastic is missing, to crack the concrete below. Hence, the corner cracks are formed.
The good news about this type of crack is the foundation corner crack is not a structural concern and does not affect the function of the foundation. It generally becomes a small detail to manage for water and insect intrusion.
