What Causes Cracks in Basement Walls?

Shrinking

• As concrete dries and cures, it shrinks because the water used to mix it is evaporating. The shrinking effect of concrete contributes to many fine, relatively harmless cracks in basement walls, says Inspectapedia. Shrinkage cracks run straight and mostly vertical. If lots of shrinkage cracks appear, especially in one wall or area, the mix of concrete used for this part of the foundation may be weak. Fast curing also causes a high amount of cracking from shrinkage.

Settlement

• Most soil on home sites is too soft and loosely packed to support a foundation properly. In this soil, concrete footers offer the extra support. If the foundation was poured over the soil or the footers were installed incorrectly, diagonal cracks appear as the structure settles, according to the National Ready Mix Concrete Association. The soil or footings shift due to frost in the soil, causing expansion or extra moisture that causes compaction. The foundation may need reinforcement if the cracks widen, indicating severe settlement.

Exterior Damage

• The horizontal basement wall crack indicates the most serious damage. Horizontal cracks indicate extreme pressure coming from the outside of the foundation wall, says Mattson MacDonald Young Structural Engineers. If your basement walls weren't designed properly, they can't support the weight of the soil pressing in on all sides. The wall also bows inward as the pressure increases. Without some kind of repair or reinforcement, the cracked wall can collapse, which causes serious damage to the rest of the home as well.

Lack of Joints

• All poured concrete is susceptible to cracking as it cures, but there is a way to limit where it occurs and how extensive it is. Control joints are seams cut into the concrete as it cures or after it hardens that let the walls crack in specific areas, according to the National Ready Mix Concrete Association. Using control joints allows you to place cracks where they will have the least impact on the strength and durability of the wall.