Reading Exterior Foundation Cracks

The shape of an exterior crack is a clue to what’s happening underneath. Here’s how to read vertical, horizontal, and stair-step cracks on a Central Texas home.

Vertical & stair-step

Vertical and stair-step cracks usually trace to differential settlement — one part of the slab dropping. Growing ones point to settlement repair.

Horizontal cracks

Horizontal cracks in a foundation wall can signal lateral soil pressure and deserve prompt attention. Measure before assuming the worst.

What to do

Photograph and date the cracks, then book a free survey if they grow. We read these patterns daily across New Braunfels and Seguin.

What Exterior Foundation Cracks Are Actually Telling You

A crack on the outside of a Central Texas foundation is not merely cosmetic damage — it is a record of how the soil beneath that slab has moved, when it moved, and in which direction. Reading those cracks correctly requires understanding the Blackland Prairie and Edwards Plateau soils that dominate the San Antonio–Austin corridor. East of the Balcones Escarpment, Houston Black clay carries a plasticity index routinely between 40 and 60, meaning the soil shrinks dramatically during dry summers and swells with equal force after winter rains. West of the escarpment, thin residual soils over fractured Edwards limestone behave differently — less volume change overall, but differential movement where limestone pinnacles are present. The crack pattern on your exterior wall reflects which of these mechanisms is at work.

Stair-step cracks running diagonally through mortar joints in a brick veneer are the most common sign of differential settlement in expansive clay. When one corner of a slab loses more moisture support than the adjacent section — typically because a large tree is drawing water from a narrow zone, or because a downspout concentrates runoff near one pier location — that corner drops relative to the rest. The masonry, being brittle, cannot follow without cracking. The direction of the stair-step tells you which side is lower: cracks that widen toward the bottom indicate the affected corner has dropped; cracks that widen toward the top suggest the center of the slab is heaving upward due to soil expansion beneath an area that stays wet year-round. Both require investigation, but they call for opposite remedies, and confusing them is a costly mistake.

Horizontal cracks at a consistent height along a stem wall or grade beam are a different category entirely. They typically result from lateral soil pressure — particularly when fill was placed against the exterior after construction, or when poor drainage allows water to pond against the wall and drive hydrostatic pressure inward. In contrast, vertical cracks spaced at regular intervals along a poured-concrete grade beam often indicate shrinkage curing, and many of these are cosmetically sealed rather than structurally repaired. The key diagnostic is whether the crack is active or dormant. An active crack will show fresh concrete powder or brick dust at its edges, may have measurable offset from one side to the other, and will widen and narrow with the seasons. A dormant crack that has been stable for years and shows no differential displacement across its faces is a much lower priority.

Because Central Texas soils have an active zone — the depth at which seasonal moisture change drives volume fluctuations — that commonly extends 10 to 20 feet below grade, surface-level drainage corrections alone cannot address advanced settlement. Concrete pressed piers transmit load only to the depth of refusal, which in some areas still falls within the active zone. GroundLock's galvanized steel piers are driven hydraulically to load-bearing strata below the active zone, anchoring the foundation to material that does not respond to seasonal rainfall cycles. That distinction matters when you are reading exterior cracks caused by long-term cumulative settlement rather than the back-and-forth of seasonal movement.

• Stair-step vs. horizontal orientation: diagonal stair-step cracks signal differential settlement or heave; horizontal cracks along a stem wall point to lateral earth or hydrostatic pressure — each has a different repair path.
• Crack width and offset matter: a hairline crack less than 1/16 inch with no vertical displacement across its faces warrants monitoring; a crack wider than 1/4 inch or with measurable offset warrants an elevation survey immediately.
• Location relative to corners and openings: cracks radiating from the corners of windows and doors indicate the slab is racking — the frame opening is distorting, and doors or windows that bind confirm the movement is ongoing.
• Drainage grade as a first check: the yard surface should fall at least 6 inches over the first 10 feet away from the foundation; flat or negative grades trap moisture against the grade beam and accelerate clay-driven movement.
• Watering program during drought: maintaining a consistent soil moisture perimeter 18 to 24 inches from the foundation edge with a soaker hose can slow active-shrinkage settlement, but it does not reverse movement that has already occurred — that requires mechanical support.

Every exterior crack investigation at GroundLock begins with a ±0.01-in. elevation survey across the full footprint, not a visual inspection alone. Elevation data maps exactly which areas have dropped and by how much, distinguishing cosmetic surface cracking from structural movement that warrants a written, engineer-backed repair plan. If you are seeing new stair-step cracks after the most recent dry season, or if cracks you thought were stable have widened or shifted, that survey is the correct first step — and it is free.

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