Why Lincoln walls crack
Clay that swells and shrinks
Most Lincoln homes sit on loess, a fine wind-blown silt, with clay in the lower layers. Wymore is the most common soil in Lancaster County. USDA data shows its subsoil is about 42 to 55 percent clay, with a very high shrink-swell rating. Crete and Pawnee soils, also common here, behave the same way. When the clay is wet, it swells and pushes on the wall. When it dries, it shrinks and lets the soil settle. That back-and-forth opens cracks and makes old ones wider.
Big swings between wet and dry
Lincoln averages about 29 inches of rain a year, according to University of Nebraska climate records, with the most in May and June. Dry years happen too. In 2012, Lincoln got only about 19 inches. A long dry stretch followed by heavy spring storms is the classic recipe for new cracks.
Frost
The City of Lincoln asks for frost-free deck footings at least 36 inches deep. Soil near the top of a basement wall freezes every winter. Wet soil swells as it freezes and pushes in on the wall. That is one reason long sideways cracks often show up a few blocks down from the top of a block wall.
Concrete shrinkage
Poured walls shrink a little as they cure. That leaves thin vertical cracks in many newer Lincoln basements. They are often harmless, but they are a common path for water.
Older walls
About 1 in 8 Lincoln homes was built in 1939 or earlier. Brick and early block walls crack along the mortar joints, often in a stair-step line.
