· by Michael Blair, Nashville's Foundation Repair
Almost every foundation in Middle Tennessee has cracks. Concrete shrinks as it cures and houses settle. What matters is the direction of the crack, its width, and whether it is still moving.
Vertical cracks
Usually shrinkage, particularly in poured walls, and usually the least concerning. They tend to be widest in the middle and taper at the ends.
They matter mainly as water paths. A vertical crack in a basement wall admits water and should be sealed, but it is rarely a structural signal on its own.
Horizontal cracks
The serious one. A horizontal crack in a block or poured wall means lateral pressure from soil outside is pushing the wall inward, and Middle Tennessee clay generates a great deal of it when saturated.
Accompanied by bowing, this needs assessment rather than sealing. Sealing a horizontal crack hides the movement without addressing it.
Stair-step cracks
In block walls, cracks following the mortar joints in a stair pattern usually indicate differential settlement — one part of the footing has moved relative to another.
Width matters here. Hairline stair-stepping is common; a joint you can fit a coin into, especially with displacement, is not.
- Vertical, hairline: shrinkage, seal against water
- Horizontal with bowing: lateral soil pressure, get it assessed
- Stair-step with displacement: differential settlement
- Widening over months: active movement
- Cracks with doors and windows sticking: check together
Monitor before you commit
Mark each end of a crack with a pencil and the date, and measure the width. Photograph it. Check again in three months and after a wet season.
Middle Tennessee clay moves seasonally, so a crack that opens in a wet winter and closes in summer is behaving differently from one that only ever gets wider.