Clay Soil and Bowing Basement Walls in Des Moines

Des Moines sits at the southern end of the Des Moines Lobe, the last glacier to reach Iowa, and the Iowa Geological Survey describes its till as a calcareous clay loam. Clay-rich soil holds water, swells when wet and shrinks when dry. After a long wet spring and a freeze-thaw winter, that pressure works on basement walls year after year.

The warning signs. A long horizontal crack near mid-height of a block wall, stair-step cracks at the ends, a wall leaning in at the top, or a gap at the sill plate. Measure the bow from a plumb line and take dated photos. See bowing wall repair.

Carbon fiber straps are bonded inside the wall and hold it where it is, at $4,000 to $12,000 per project (Fixr, January 2026). More on straps.

Wall anchors use plates buried in the yard at least 10 feet out and can be tightened over time; Acculevel priced them at about $830 to $1,000 each (2020). They need open yard, which narrow city lots may not have. More on anchors.

Steel beams bolted at the floor and joists are the inside option where the yard is tight.

Fix the water too. Soil pressure peaks when the soil is saturated. Downspouts, grading and drainage belong in the same plan. See yard drainage.