Sinking Foundation Repair Alamo Heights, TX.

The houses along the older streets of Alamo Heights weren't built on a problem so much as on a rhythm. The high-plasticity clays near the Olmos Basin take on water in a wet winter, swell, then give it back through a dry Central Texas summer and contract, and they have been doing that under these slabs and pier-and-beam structures since the neighborhoods were first platted. Most years the movement is invisible. Over decades, it isn't.

What homeowners eventually notice is one-directional: a corner that keeps dropping a little further each drought and never fully comes back, because each year the soil pulls moisture away faster than later rains can replenish it at depth. That's not neglect, it's what building on active-zone soil does without piers anchored below the layer where the moisture keeps cycling. The fix is to take the load off that moving clay entirely.

How deep the moving soil actually runs here

The active zone, the depth where clay volume changes with the seasons, typically reaches 10 to 20 feet below grade in Central Texas, and the Olmos Basin area can push it deeper where the clay column is thick. Within that band, plasticity indices commonly run 30 to 60 or higher, which is another way of saying the soil has an enormous appetite for changing size as its water content moves up and down.

That number is the whole reason short fixes fail in this part of Bexar County. A pressed-concrete pier that stops inside the active zone is anchored to the same material that's misbehaving; it holds at first, then drifts as the clay around it moves. To actually arrest a sinking corner, the support has to reach past the moving column to something that doesn't respond to rainfall.

Below the active clay sits the stable bearing material, dense caliche or limestone bedrock that holds its position regardless of the season. Reaching it, rather than hitting an arbitrary depth on a spec sheet, is what determines where a pier stops and the foundation finally rests on ground that stays put.

From low corner to locked-off in four stages

Signs the clay is winning under your house

Differential settlement shows up at the finishes long before it shows up in your peace of mind. Watch for these around an Alamo Heights home:

• Stair-step cracks in brick veneer running diagonally through the mortar joints, the masonry absorbing shear as one section drops faster than another.
• Doors that bind seasonally and never return to plumb after a dry stretch, which points to cumulative settlement rather than ordinary swelling.
• A floor that pitches noticeably toward one corner or feels bouncy over what should be solid slab.
• Drywall cracks fanning out from door and window corners, plus gaps opening where trim meets the ceiling.
• Cracks in the slab itself or separation at the garage floor, often the first place a low corner reveals itself.

Questions Alamo Heights homeowners ask us