Foundation repair · Bastrop County County, TX
In Bastrop County the sand does not swell and the terrace clay swells 7 to 12 percent, so the same crack can mean two different repairs.
Most foundation trouble in Bastrop County traces back to one of two opposite problems, and which one you have depends on where in the county you sit. On the clay terraces and uplands the soil swells when it rains and shrinks when it dries, and the house rides that movement. Out in the Lost Pines the ground is deep loose sand over an acid clay layer, and the trouble is bearing, washout and a high water table instead. We look before we quote, because about a third of the inspections we run end with no repair needed.
The ground under Bastrop County County
Why the Lost Pines sand and the terrace clay fail differently
There is no limestone shelf under this county. Bastrop County sits at 400 to 600 feet above sea level on the Gulf Coastal Plain, well east of the Balcones Escarpment, and the bedrock here is Eocene sand, clay and shale laid down in a belt that strikes northeast to southwest and dips toward the coast. That dip is the whole reason the ground changes as you move southeast across the county instead of staying uniform. The county covers 891 square miles, 570,240 acres, and the soil holding up a house on one side of it behaves nothing like the soil on the other. The older unit at the surface is the Wilcox Group, which divides in ascending order into the Hooper, Simsboro and Calvert Bluff formations. The Wilcox is an ancient delta complex, so what is exposed at or near the surface is fine to coarse sand, sandy clay and shale with lenses of lignite and limestone. The Simsboro is the main water producer, typically 175 to 300 feet thick in this county and locally as thin as 100 feet. Sitting above the Wilcox is the Carrizo Sand, a river deposit that is light to dark gray, fine to coarse grained, loose, poorly sorted and thickly bedded, forming a continuous sheet about 100 feet thick in Bastrop County with a reported maximum of 375 feet. That Carrizo and Wilcox outcrop belt is why the northwest half of the county is clay and shale ground while the central and eastern reach turns to deep loose sand. The soil survey block diagrams show the same trend from the top down. The Lost Pines sands sit on sandy and loamy materials with interbedded sandstone, the Axtell and Tabor terraces sit on clayey materials interbedded with shales and sandstones, and the Crockett and Wilson uplands sit on alkaline marine clayey materials or shale. Cutting diagonally across all of it is the Colorado River, which has laid down a valley of Quaternary terraces and alluvium wide enough that the alluvium works as an aquifer in its own right.
The terrace clay that swells 7 to 12 percent
Patilo, Demona and Silstid, about 32 percent of the county and the largest of the five soil associations the USDA maps here. Deep loose fine sand and loamy fine sand over acid mottled sandy clay. The survey names the limitations for urban use in this belt as the sandy surface layer, permeability and a high water table, and it does not name shrink-swell at all. Houses out here move because sand carries load poorly, washes out from under edges, and sits over a wet clay layer, not because the ground is swelling. Pier design changes accordingly, and so does the drainage work that goes with it.
The Lost Pines sand that moves without swelling
About 29 percent of the county, the second-largest association, on nearly level to gently sloping ridgetops and terraces. Clay content of 35 to 55 percent, linear extensibility of 7 to 12 percent depending on which series you are standing on, and very slow permeability. Tabor is the wetter of the two, classified Oxyaquic, meaning the profile stays saturated for periods, so the lot holds a perched wet layer over a clay that swells. This is where seasonal slab movement looks textbook, worst at the corners and along the drip line where the moisture swing is biggest.
The Crockett and Heiden uplands
Crockett-Wilson covers about 18 percent of the county and Behring-Crockett-Heiden another 11 percent, and for both the survey lists the same urban limitations, shrink-swell potential, corrosivity and permeability. Heiden is a true Vertisol, the most aggressive shrink-swell class in the classification system. The corrosivity flag is the part people skip past, and it is the one that decides what a pier is made of rather than just how deep it goes. We install steel piers and hybrid piers, and on this ground the material question gets asked out loud.
The Colorado bottom where the water sits high
Bosque, Smithville and Norwood along the river, about 10 percent of the county, running diagonally through Bastrop and Smithville on Quaternary terraces and alluvium. The limitation the survey names here is flooding, not shrink-swell. On these lots the grading, the downspouts, the french drains and the crawl space moisture control usually carry more weight than pier depth, and a floodplain review is more likely to touch the job than a building permit is.
Straight from the soil survey
What the USDA maps under Bastrop County County.
The USDA soil survey is published at the county level, which is why this table lives on this page instead of a city page. These are the series that cover the most ground in Bastrop County, what the federal descriptions actually say about each one, and what that behavior does to a house. Linear extensibility is the number worth understanding. It is how much a sample of that soil grows and shrinks between wet and dry, expressed as a percentage, and the higher it runs the more a slab has to ride.
| Soil series | Share of county | How much it swells | What that means for a foundation |
|---|---|---|---|
| Axtell | About 48 percent of the Axtell-Tabor association, which USDA maps across about 29 percent of Bastrop County, so roughly 14 percent of the whole county on its own | LEP ≈ 10% | Classified Fine, smectitic, thermic Udertic Paleustalfs with 35 to 50 percent clay in the particle-size control section and a linear extensibility of 7 to 10 percent in the upper 100 cm, on a solum deeper than 150 cm with no bedrock contact, so a pier here has to pass through a lot of moving ground before it reaches anything that holds still. |
| Crockett | About 48 percent of the Crockett-Wilson association, about 18 percent of the county, plus about 28 percent of the Behring-Crockett-Heiden association, about 11 percent of the county, so it turns up in two separate associations | Shrink-swell potential, corrosivity and permeability, the urban limitations the survey names for both associations it appears in | Brown loam surface over mottled clay on the uplands, and because the survey flags corrosivity right alongside shrink-swell, this is ground where the pier material gets decided deliberately and not just the pier depth. |
| Patilo | About 30 percent of the Patilo-Demona-Silstid association, which the survey puts at about 32 percent of Bastrop County, the largest of the five associations | Not named by the survey here, the limitations listed are the sandy surface layer, permeability and a high water table | Fine sand at the surface, light brownish gray over very pale brown, with acid mottled sandy clay loam beneath, so what fails under a Lost Pines house is bearing capacity, erosion and a wet layer rather than a clay that swells. |
| Tabor | About 25 percent of the Axtell-Tabor association, which covers about 29 percent of the county, on nearly level to gently sloping ridgetops and terraces | LEP ≈ 12% | Classified Fine, smectitic, thermic Oxyaquic Vertic Paleustalfs, 45 to 55 percent clay with a linear extensibility of 7 to 12 percent in the upper 51 cm of the argillic horizon, soil depth of 152 to more than 203 cm, moderately well drained with very slow permeability, and the Oxyaquic part is what hurts, because the profile stays saturated for stretches and the lot ends up holding a perched wet layer directly over a clay that swells. |
| Demona | About 23 percent of the Patilo-Demona-Silstid association, about 32 percent of the county | Not named by the survey, same limitation set as Patilo, sandy surface layer, permeability and a high water table | Loamy fine sand surface on foot slopes and in drainageways over acid mottled sandy clay, and the drainageway position concentrates water, so deep loose sand over clay becomes a bearing and erosion problem well before it becomes a swell problem. |
| Silstid | About 13 percent of the Patilo-Demona-Silstid association, about 32 percent of the county | Not named by the survey, sandy surface layer, permeability and a high water table | Loamy fine sand over acid mottled sandy clay loam over clay loam, again on foot slopes and in drainageways, rounding out the sandy third of the county with the same urban limitations Patilo and Demona carry. |
| Heiden | About 14 percent of the Behring-Crockett-Heiden association, about 11 percent of the county, on side slopes and foot slopes | High, a true Vertisol, with cracks 1 to 8 cm wide staying open 90 to 150 cumulative days in a normal year | Classified Fine, smectitic, thermic Udic Haplusterts with 40 to 60 percent clay in the control section and a densic contact at 100 to 203 cm, and the cracks the description reports, 1 to 8 cm wide at a depth of 30 cm or more during dry spells, that is half an inch to three inches, open four to five months out of the year, are the mechanism behind a whole season of movement. |
Linear extensibility (LEP) is the USDA's measure of how much a soil changes volume between wet and dry. Higher numbers move houses.
Where we work in Bastrop County County
The Bastrop County County towns we cover.
Each one has its own page, because the ground changes inside this county and the local pattern is what matters when you are standing in the house.
What gets built here, and when
Older river town stock and newer houses out in the pines
Bastrop County grew late, grew fast, and grew mostly outside a city. The Texas Water Development Board count reported by Texas Parks and Wildlife puts the 1990 county population at 38,263, of which 26,074 people, about 68 percent, lived on unincorporated land. Bastrop city had 4,044 people, Elgin 4,846 and Smithville 3,196. The same table projected the county to 63,901 by 2010 and 106,153 by 2050, close to three times the 1990 count. Those later figures are 1998 projections rather than counts, so read them as direction and not gospel, but the shape has held. The great majority of the housing a repair crew sees here went up after 1990, on rural acreage and subdivision lots rather than inside an old town grid, and the named towns are a small share of the total. The older stock sits in the historic cores. Bastrop and Elgin are nineteenth century towns with small districts of pre-war houses, and those cores are where pier and beam construction lives in this county. Pier and beam here rests on the same clay terraces as everything else, so the failure pattern reads differently. You get sagging interior beams and settled or rotted interior supports rather than a slab tilting as one piece. That changes the repair. Interior support work, sill and beam replacement and crawl space moisture control do more good in those blocks than a ring of exterior piers would.
Permits in Bastrop County County
Who signs off on a foundation repair here.
Two different worlds sit inside one county line here, and the split matters because roughly two thirds of the people in Bastrop County live on the unincorporated side. Out in unincorporated Bastrop County, Texas counties generally do not carry building code authority the way cities do, and Bastrop County follows that pattern, so a county building permit is not normally issued for foundation repair out there. We confirm your address with the county before anything is scheduled rather than taking the pattern on faith. What the county does administer is a separate set of approvals that can still touch a foundation job, including a county development permit, floodplain review and elevation certification through the county Floodplain Administrator, driveway and road access permits, on-site sewage facility permits, and review under the Lost Pines Habitat Conservation Plan, which applies to residential and commercial construction in the county because of the Houston toad. Near the river or on a mapped flood lot, the floodplain side is usually the one that governs. Inside a city limit it goes back to that city's building official. The City of Bastrop confirms permits under its adopted building codes and points applicants to its building department. Elgin sets its own requirements, so we ask the city rather than assume. An engineer letter is not standard for foundation repair in this county, though a lender, a buyer or an insurer may still want one for their own file. Our inspectors are ICC certified, not engineers, and we say so up front. We handle the permits and approvals that the job actually needs.
Costs, warranty and inspections
The straight numbers in Bastrop County County.
Straight answers
Foundation questions people ask in Bastrop County County.
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