Brazos Valley Clay Soils and Your Foundation

Brazos bottom clay and clay pan uplands shrink when dry and swell when wet. Steady moisture and good drainage reduce how much your house moves.

Get a price from a local pro

Free to use
One local company, not a list
No obligation to hire

Referral website, not the contractor. How it works

Foundations around Bryan, College Station and Navasota move mainly because the clay under them shrinks in dry weather and swells in wet weather. You can't change the soil, but you can reduce how much its moisture swings.

Brazos Valley Foundation Repair is a referral website, not a foundation repair company. We send your request to one independent local foundation repair company. You never pay us; companies we refer you to may pay us for referrals. If you already see signs of movement, send a request with the form.

The soils under Brazos Valley homes

Brazos County lies between the Navasota and Brazos rivers. The Texas State Historical Association describes its soils as "alluvial to sandy," with the northern third of the county in the Blackland Prairie and the rest in the Post Oak Savannah. In Brazos County, three kinds of ground matter most for foundations.

Brazos River bottom clay. On the floodplains, the best-known clay is the Ships series. USDA's official description puts its clay content at 60 to 70 percent and calls it "very sticky and very plastic" and very slowly permeable. When it dries, cracks at least 1 cm (0.4 in) wide reach more than 20 inches down and stay open 60 to 90 days in most years. It forms mainly along the Brazos and Colorado rivers.

Loamier bottomland. Not all bottomland is that heavy. The Weswood series, also found mainly along the Brazos and Colorado rivers, averages 18 to 35 percent clay in its control section. Soils change across short distances, so check the map for your own lot.

Clay pan uplands. Texas Parks and Wildlife describes Post Oak Savannah soils as sands and sandy loams on the uplands, clay to clay loam in the bottoms, and "dense clay pan underlying all soil types," which is why the region is sometimes called the "Clay Pan Savannah." That clay pan is nearly impervious to water and sits only a few feet down.

Grimes County, around Navasota. TSHA says upland soils there are gray sandy loams over clayey subsoils, and bottomland soils along the rivers and creeks are dark, loamy to clayey alluvium.

To see the mapped soil under your own lot, use USDA's free Web Soil Survey and draw a box around your address.

Why clay moves a foundation

Clay particles take on water between microscopic layers. Dr. Jake Mowrer, a soil scientist with Texas A&M AgriLife Extension, explained it to FOX 7 Austin in 2022: "When they get wet, they swell, and when they get dry, they shrink."

The ASCE Texas Section notes that shrinking and swelling clay can move residential foundations, and lists other factors that make it worse: leaking plumbing, trees, poor drainage, landscaping practices and problems with the original design or construction.

The trouble usually comes from uneven moisture. If one side of a house dries out under a big tree while the other side stays wet from a downspout, the slab bends. That's why ASCE's guidelines stress near-uniform soil moisture on all sides of the foundation.

Drought, rain and the Brazos Valley climate

TSHA puts Brazos County's average rainfall at about 39 inches a year, but averages hide the swings. In 2011, Texas recorded its driest year on record, 14.88 inches statewide, according to the National Weather Service. Long dry spells pull moisture out of the clay and open cracks beside the foundation; heavy rain refills them and swells the soil again.

Freezes can break pipes. After the February 2021 winter storm, the City of College Station waived permit fees for storm-related repairs through March 7, 2021. A leaking pipe under or beside a slab adds water to the clay, and the ASCE guidelines list leaking plumbing as a foundation factor.

What homeowners can do

The ASCE Texas Section's repair guidelines include several non-structural steps that may improve foundation performance and reduce future movement. They're worth doing whether or not you ever need piers.

Keep soil moisture steady. ASCE says keeping soil moisture near uniform on all sides of the foundation may help, and advises caution against excessive watering. In the FOX 7 report, a Central Texas foundation repair owner said the aim is to "keep the moisture as consistent as possible": water in summer, and don't let water pool against the house in wet seasons.

Fix your gutters and downspouts. ASCE says uncontrolled roof runoff causes erosion and ponding near the house, and that downspouts should discharge well past the edge of the foundation and past any planting beds, into well-drained areas.

Check the grading. ASCE recommends, where practical, a slope of about 5 percent (6 inches over 10 feet) away from the foundation for the first 10 feet. Water standing against the slab after rain is a sign the grading needs work.

Think about trees. ASCE notes trees or large shrubs near a foundation may shrink the soil under it. Removing a tree can stop that, but can also cause upheaval as the soil rewets, especially if the tree predates the house. Pruning may be a prudent alternative. Talk to an arborist before cutting roots or installing root barriers.

Watch the plumbing. A water bill that jumps for no reason, or the sound of running water with every tap off, can mean a leak under the slab. Have a plumber test the lines.

When to call for an evaluation

Get the foundation looked at if you notice several of these together, or if they get worse over a season:

Doors or windows that start sticking or won't latch
Diagonal cracks at the corners of doors and windows
Stair-step cracks in brick
Floors that slope, bounce or feel soft
A gap opening between the soil and the slab edge in dry weather

Take dated photos so you can show how fast things are changing. You can ask a repair company for an evaluation, or hire an independent Texas-licensed professional engineer (P.E.) for a report; our foundation inspection page explains the difference.

Slab foundation repair and pier and beam foundation repair explain how each type is fixed.
House leveling explains what lifting can and can't do.
The foundation repair cost guide lists typical prices.
Foundation repair in College Station and Navasota cover local permits.

Sources (10)

Last updated 2026-10-23