Coastal clay and foundations around Pearland

Brazoria County ground

The Handbook of Texas places Brazoria County on the Gulf Coast prairie at the mouth of the Brazos River. Its highest point, Damon Mound, is just 146 feet above sea level. The county's soils are mostly alluvial loams and clays, which the Handbook notes are highly productive when well drained. The Brazos splits the county, with hardwoods across the western third and prairie over most of the rest.

The Texas Almanac adds that the Coast Prairie is level to gently undulating with slow surface drainage, and that its upland soils are mostly deep, dark-gray clay loams and clays.

One coastal clay, in numbers

Lake Charles is a clay soil the USDA describes as extensive in southeast Texas between the Colorado and Trinity rivers. Its official series description gives these figures:

Your lot may be different, and building pads often include fill. To see what's mapped under your own house, use the USDA's Web Soil Survey.

Wet, then dry

Soil that drains slowly stays wet after heavy rain, and clay swells when wet. In a dry stretch the same clay shrinks and cracks. When one side of a house dries or wets faster than the other, the slab can move unevenly. The Texas Section ASCE repair guidelines recommend:

• Grading the first 10 feet around the house to fall away at 5 percent or more
• Running downspouts well past the foundation into areas that drain
• Keeping moisture fairly even on all sides, without overwatering

Signs to note

Stair-step cracks in brick, diagonal cracks at door corners, doors that won't latch and floors that slope are common signs. Date-stamp photos and compare over a few weeks. If the changes continue, get an evaluation.