Texas Foundation Repair by Soil & Neighborhood

Every texas foundation repair job starts with the same question: what’s the ground doing underneath the slab? Across the Texas metros G.L. Hunt Foundation Repair serves, the answer changes block by block. Expansive clay swells when it’s wet and shrinks hard when it dries out, and that movement is what cracks slabs, sticks doors, and opens gaps at the baseboards.

We’ve mapped soil type, Plasticity Index, and shrink-swell risk down to the ZIP code for every city we serve, using official USDA-NRCS soil series data and NOAA’s 1991–2020 rainfall normals , not guesswork. 

Analyse the soil report of your city and check your ZIP’s soil risk, or read on for how to make sense of the numbers.

Texas Foundation Repair – Comparison Table

Austin and San Antonio currently top the list for peak PI, but “worst-case” only tells part of the story, within every one of these cities, risk varies a lot by ZIP. A slab in Steiner Ranch (Austin, PI ~10–20) is sitting on a completely different soil than one two miles away in East Austin (PI ~35–50). Click through to your city above to see exactly where your ZIP falls.

What is Plasticity Index (PI)?

Plasticity Index measures how much a soil’s volume changes between its wettest and driest states, in plain terms, how much it swells and shrinks. Soil labs test this directly; the higher the number, the more the ground moves with the seasons.

• PI under ~20: Low to moderate movement. Usually shallow, rocky, or sandy soils.
• PI ~20–35: Moderate to high movement. Enough to cause problems over time, especially with poor drainage.
• PI above ~35: Very high movement. This is expansive clay, Houston Black and its relatives, and it’s the primary driver of foundation repair calls across Central and North Texas.

A high-PI soil isn’t a guarantee your foundation will fail, but it does mean drainage, gutters, and consistent moisture around the slab matter a lot more than they would on milder ground.

Why this varies so much within one city

The same geological forces that built Texas laid soil down unevenly, and city boundaries don’t follow soil boundaries. Austin’s soil splits hard at I-35, deep expansive Blackland Prairie clay to the east, thinner soil over Edwards Plateau limestone to the west. 

San Antonio has a similar west-to-east gradient across Bexar County, from shallow rocky soil in the north to deep black clay through the central belt. Waco sits deeper in Blackland Prairie territory overall, but even there, creek-adjacent neighborhoods on Bosque soil see far less movement than the Houston Black areas nearby.

That’s why we map risk by ZIP instead of by city, a single citywide answer would be misleading for a lot of the people asking.