# Post Tension Slab: A Baton Rouge Homeowner's Guide

> What is a post tension slab? Concrete squeezed by steel cables. How to tell if your Baton Rouge house has one, why not to drill it, and how it's repaired.

URL: https://foundationrepairbatonrougelouisiana.com/blog/post-tension-slab/

# Post Tension Slab: What Baton Rouge Homeowners Should Know

By [Jonathan Dyer](https://foundationrepairbatonrougelouisiana.com/authors/jonathan-dyer/) · Published October 4, 2026 · Last updated October 4, 2026

![Post Tension Slab: What Baton Rouge Homeowners Should Know](https://foundationrepairbatonrougelouisiana.com/images/hero-post-tension-slab-baton-rouge.webp)

What is a post tension slab? A post tension slab is a concrete foundation with steel cables (tendons) running through it that are pulled tight after the pour, squeezing the concrete so it resists cracking on Baton Rouge's shrink-swell clay. The catch: you must not drill or cut it blind.

### Key Takeaways

-   Each residential tendon is a 7-wire steel strand pulled to about 33,000 pounds once the concrete reaches 2,000 psi, typically 3 to 10 days after the pour — [Concrete Network](https://www.concretenetwork.com/post-tension/basics.html)
-   House slabs commonly space tendons about 48 inches apart, so a random hole has a real chance of hitting one — [Concrete Network](https://www.concretenetwork.com/post-tension/basics.html)
-   The Post-Tensioning Institute's DC10.5 standard, first published in 1980, underlies "essentially all" unbonded post-tensioned slabs-on-ground in North America — [PTI, 2020](https://www.post-tensioning.org/Portals/13/Files/PDFs/Education/positionstatement.pdf)
-   Expansive soil already costs Louisiana about $66.2 million a year in property losses, which is why engineers specify post-tensioning here — [Frontiers in Built Environment, 2021](https://www.frontiersin.org/journals/built-environment/articles/10.3389/fbuil.2021.754761/full)
-   Finding the tendons with ground-penetrating radar costs about $1,000 to $3,000 a day, or hourly with a 2-hour minimum — [SPH Engineering, 2026](https://www.sphengineering.com/news/gpr-cost)
-   A settled post tension slab is still repairable, usually with exterior pilings and drainage work rather than interior cuts

## What is a post tension slab?

A post tension slab is a slab-on-ground foundation reinforced with unbonded steel tendons that are stressed after the concrete hardens. “Post” means the tensioning happens after the pour, which is the difference from precast, pre-tensioned concrete.

Before the pour, crews lay out tendons on chairs across the slab area in both directions. [Concrete Network’s construction guide](https://www.concretenetwork.com/post-tension/basics.html) describes each tendon as “seven high-strength steel wires wound together and placed inside a plastic duct.” The sheath and grease inside it keep the steel from bonding to the concrete, so it can stretch.

Once the concrete has reached about 2,000 psi, a hydraulic jack at the slab edge pulls each tendon to roughly 33,000 pounds. A 100-foot tendon stretches about 8 inches. Steel wedges then lock it against an anchor plate cast into the edge, and the jack’s pocket is filled with grout.

## Why are post tension slabs used on Baton Rouge clay?

Post tension slabs are used here because the Capital Region’s clay swells when wet and shrinks when dry, and that movement bends an ordinary slab. Compression from the tendons lets the slab ride that movement with fewer and tighter cracks.

The [USDA soil survey of East Baton Rouge Parish](https://archive.org/details/eastbatonrougeLA1968) rates soils such as Sharkey clay as high shrink-swell and notes that much damage to building foundations comes from soils shrinking and swelling. A 2021 LSU-led study in [_Frontiers in Built Environment_](https://www.frontiersin.org/journals/built-environment/articles/10.3389/fbuil.2021.754761/full) put Louisiana’s average yearly expansive-soil property loss at $66.2 million, rising to about $91.8 million by 2050.

The [Post-Tensioning Institute (PTI)](https://www.post-tensioning.org/education/ptapplications/slab-on-ground.aspx) explains the mechanism: “The compressive stresses resist the anticipated tension stresses induced by the soil movements, enhancing the performance over a non-prestressed foundation.” PTI adds that post-tensioning keeps “any cracks that might form tight,” and that savings come from using less concrete, steel and excavation.

That is why many newer subdivision homes in Prairieville, Gonzales and the rest of Ascension and East Baton Rouge parishes sit on post-tensioned slabs over fill pads. Our [Prairieville foundation repair page](https://foundationrepairbatonrougelouisiana.com/service-areas/prairieville/) covers why those fill pads keep settling for years after the house is built.

## How does a post tension slab compare to a rebar slab?

A post tension slab puts the whole slab into active compression, while a conventional slab uses passive rebar or wire mesh that only works after the concrete has already cracked. That is the core difference for a homeowner.

Feature

Post tension slab

Conventional rebar/mesh slab

How the steel works

Tendons stressed to about 33,000 lb each, squeezing the concrete

Rebar sits passive until the concrete cracks

Design standard

PTI DC10.5 (IRC 2024 adds Section R506.2 for it)

Standard IRC slab provisions

Crack behavior

Cracks tend to stay tight

Cracks can open wider over time

Drilling and coring

Must locate tendons first (GPR or plans)

Lower risk; rebar cuts are rarely critical

Interior repair cuts

Possible, but tendons must be mapped

Routine

Typical Baton Rouge use

Many newer subdivision homes on fill

Older brick ranches from the 1960s-80s

Louisiana adopted the 2021 IRC statewide effective January 1, 2023, so the 2024 code’s new post-tension section is not yet the local baseline. In practice, PTI’s own 2020 position statement says DC10.5 is the basis of “most commonly available slab-on-ground design software,” so a post-tensioned house built here was very likely designed to it either way. For a wider comparison of slab and raised homes, see our [pier and beam vs slab guide](https://foundationrepairbatonrougelouisiana.com/blog/pier-and-beam-vs-slab-foundation/).

## How can you tell if you have a post tension slab?

You can usually tell from the outside of the house in about ten minutes. Check these three things, in this order:

1.  **The garage stamp.** Look on the garage floor and the wall between the garage and the house for a stamp or sign warning that the slab is post-tensioned. Concrete Network notes that “many post-tensioned slabs will be stamped to alert the owner and any renovation contractors.”
2.  **Grout patches along the slab edge.** Walk the perimeter and look at the exposed face of the slab. A line of small, round, evenly spaced patches, a few feet apart, marks the tendon anchors.
3.  **The plans.** The builder, the parish permit file or a previous owner may have a foundation plan that shows the tendon layout. If none of these settle it, a [ground-penetrating radar](https://www.sphengineering.com/news/gpr-cost) scan will.

Do not rely on the stamp alone. On the [InterNACHI inspector forum](https://forum.nachi.org/t/post-tension-slab-labeling/23117), Jeffrey Pope wrote that “in residential, the slab should be stamped. Generally it’s done in the garage.” But two Texas inspectors in the same 2007 thread said they had rarely or never seen one on the many post-tensioned houses they inspected. A missing stamp proves nothing.

## What happens if you drill into a post tension slab?

If you drill into a post tension slab and miss the tendons, nothing happens. If you nick or sever one, the slab loses part of its compression in that strip, and the stored energy in a cut tendon can release violently.

Engineering firm [EVstudio](https://evstudio.com/damaged-post-tension-tendons/) lists the repair options an engineer may choose: leave a tendon with a single broken wire in place, abandon it and re-grout the pocket, thread in new strand and re-stress it, or splice it, where “a coupler is installed to attach new strand to the existing in-place steel.” Its bottom line: “the cost to repair a tendon generally far exceeds the cost of locating it properly before beginning any slab modifications.”

Here is how that plays out in real life. In 2017, a buyer of a new-build townhouse posted on the [InterNACHI forum](https://forum.nachi.org/t/post-tension-cable-problem/119687) that a framing subcontractor had drilled into and broken a tendon in her 8-inch slab, and she only found out by spotting it herself. The builder told her it was fixed with a coupler and a PVC sleeve and re-tensioned, “but not to the original extent.” Inspector Chuck Evans advised that the repair “should have been specified, inspected and signed off by the Engineer of Record,” and Dan Bowers urged her to bring in her own structural engineer before it was covered up.

## Do post tension slabs crack or fail?

Post tension slabs do crack, but the cracks are usually small and tight. Real failures come from how the slab was built, the soil it sits on, or water reaching the steel, rather than from the system itself.

Michael Dickens, CEO of BuildIQ, wrote in [_Pro Builder_](https://www.probuilder.com/construction/quality-matters/article/55195933/how-to-avoid-cracks-in-post-tensioned-concrete-slab-foundations) that three installation errors cause most cracking: uneven slab thickness, stressing too late (after the 4-to-10-day window, when the concrete is too strong to close cracks), and a badly placed slip sheet. He put builders’ cost to repair slab cracks at $5,000 to $10,000.

The second weak point is the anchor at the slab edge. In 2024, a North Dallas homeowner posted [photos of exposed tendon end caps](https://forum.nachi.org/t/exposed-post-tension-cable-end-caps/244575) where the grout had crumbled. Texas structural inspector Emmanuel Scanlan replied that “this is not a cosmetic issue,” because moisture can corrode the anchor until it fails. He recommended at least an inch of chloride-free, non-shrink grout over each cap.

The third is the ground. Post-tensioning keeps the slab stiffer, but it does not stop a fill pad from consolidating or a dry corner from shrinking away. When that happens, the whole stiff slab tilts, which shows up as sloping floors, sticking doors and the [signs of foundation problems](https://foundationrepairbatonrougelouisiana.com/guide/signs-of-foundation-problems/) any slab shows.

**33,000 lb**pull on each tendon at stressing[Concrete Network](https://www.concretenetwork.com/post-tension/basics.html)

**48 in**common tendon spacing in house slabs[Concrete Network](https://www.concretenetwork.com/post-tension/basics.html)

**$1k-$3k**per day for GPR scanning (or hourly, 2-hour minimum)[SPH Engineering](https://www.sphengineering.com/news/gpr-cost)

**1 in**minimum grout cover an inspector recommends over end caps[InterNACHI](https://forum.nachi.org/t/exposed-post-tension-cable-end-caps/244575)

## What do Baton Rouge homeowners say about post tension slabs?

Local opinion is split between cost and peace of mind, and it mostly comes down to soil and elevation. Two Baton Rouge-area threads on TigerDroppings, the region’s largest community forum, show both sides.

In a [May 2020 thread](https://www.tigerdroppings.com/rant/o-t-lounge/slab-or-pier-and-beam-foundation/90200999/), a Baton Rouge poster who had built on a post-tension slab a year earlier said they would probably choose pier and beam next time, because hauling in dirt for a big house pad was so expensive. Another poster with a post-tension slab on expansive soil said simply, “It depends on soil conditions.”

In an [April 2021 thread](https://www.tigerdroppings.com/rant/home-and-garden/building-house-in-prairieville-yall-use-pilings-out-here/95834023/) about building in Prairieville, a buyer from Jefferson Parish asked whether Ascension homes need pilings. One reply recommended a soil boring test “to see proper compaction before construction” or “a post tension slab.” The original poster pushed back: “I don’t see how that would stop it from tilting in the future.” That is a fair question, and the answer is in the next section.

## Can a post tension slab be repaired if it settles?

Yes. A settled post tension slab is repaired the same basic way as any slab: support the low section on deep pilings and fix the water problem that caused it. The difference is where the work happens.

Because the slab is stiff and full of tendons, most repairs go under the perimeter beam from the outside, using [pressed concrete pilings](https://foundationrepairbatonrougelouisiana.com/pressed-concrete-pilings/) or steel piers driven past the active clay. Interior pilings require cutting holes through the slab, so the tendons have to be mapped first, and many jobs avoid interior work entirely. Our [pilings vs steel piers vs helical piers guide](https://foundationrepairbatonrougelouisiana.com/guide/pressed-pilings-vs-steel-piers-vs-helical-piers/) compares the options, and [what a typical slab repair looks like](https://foundationrepairbatonrougelouisiana.com/blog/what-a-typical-slab-repair-looks-like/) walks through the job day by day.

Drainage is the other half. A downspout dumping at a slab corner keeps that clay wetter than the rest, and [foundation drainage](https://foundationrepairbatonrougelouisiana.com/foundation-drainage/) work is usually part of a lasting fix. Our step-by-step guide on [how to fix a settling foundation](https://foundationrepairbatonrougelouisiana.com/blog/how-to-fix-a-settling-foundation/) shows what to fix first. For prices, see our [foundation repair cost guide for Baton Rouge](https://foundationrepairbatonrougelouisiana.com/guide/foundation-repair-cost-baton-rouge/).

### What I'd do: my take as a concrete and steel repair specialist

If I owned a house on a post tension slab in Baton Rouge, I'd do four things. First, I'd find out for sure whether it is post-tensioned, using the garage stamp, the edge patches and the plans, before anyone drills anything. Second, I'd treat every hole as a scan job. A day of GPR is cheap next to a broken tendon, and the InterNACHI townhouse case shows how a "fixed" tendon can end up "not to the original extent."

Third, I'd walk the slab edge once a year and re-grout any anchor patch that has cracked or fallen out. Steel that is under constant tension and exposed to water is exactly the combination that industrial repair work spends its life fighting. Fourth, I wouldn't let "post-tensioned" make me complacent. The evidence says these slabs resist cracking well, but they still sit on clay and fill. If doors start sticking, I'd get the floor measured rather than assume the slab is immune.

## What should you do if you have a post tension slab?

If you have a post tension slab, the main jobs are to protect the tendons, keep the soil moisture even, and measure the slab if anything changes. Here is the short version:

-   **Before any renovation**, tell every contractor the slab is post-tensioned and insist on a scan before drilling or coring.
-   **If a tendon was hit**, stop work and get a licensed structural engineer, not just the builder, to specify and sign off the repair. Our guide on [whether you need a structural engineer](https://foundationrepairbatonrougelouisiana.com/guide/do-you-need-a-structural-engineer-for-foundation-repair/) explains what they do.
-   **If you’re buying**, ask for the foundation plan and check the edge patches. Our [buying a house with foundation repair guide](https://foundationrepairbatonrougelouisiana.com/guide/buying-a-house-with-foundation-repair/) covers what else to ask.
-   **If cracks appear**, compare them to our [crack-size guide](https://foundationrepairbatonrougelouisiana.com/guide/how-big-is-too-big-foundation-crack/). Hairline shrinkage cracks are normal; offset or widening ones are not.
-   **If doors stick or floors slope**, book an evaluation. A [free foundation inspection](https://foundationrepairbatonrougelouisiana.com/foundation-inspection/) with laser-measured readings shows whether the slab has actually moved.

### Post tension slab with cracks or sticking doors?

Book a [free foundation evaluation](https://foundationrepairbatonrougelouisiana.com/foundation-inspection/) from [Foundation Repair Baton Rouge](https://foundationrepairbatonrougelouisiana.com/). You get laser-measured readings of the whole slab and a written per-piling price, backed by 20 years of industry experience, before anyone cuts into anything.

**Methodology.** This explainer uses primary and named sources: the Post-Tensioning Institute (slab-on-ground page and its April 2020 position statement), Concrete Network's construction guide, EVstudio's engineering note on damaged tendons, _Pro Builder_, SPH Engineering's 2026 GPR price guide, the 2021 LSU-led expansive-soil study and the USDA East Baton Rouge Parish soil survey. Homeowner experiences come from three InterNACHI forum threads (2007, 2017, 2024) and two TigerDroppings threads (2020, 2021), paraphrased with links; Reddit could not be reached from our research tools. Search demand comes from a DataForSEO pull in October 2026: "post tension slab" has about 3,600 U.S. searches a month and a Baton Rouge SERP made up of engineering firms, out-of-state builders and Reddit, with no Louisiana homeowner guide. No customer stories, job counts or reviews are used, and the illustrations are AI-generated diagrams, not photos of real houses.

## Frequently asked questions

### How do I know if my house has a post tension slab?

Look for three things: a stamp or permanent sign in the garage slab warning that it is post-tensioned, a row of small round grout patches every few feet along the outside edge of the slab (each one covers a tendon anchor), and the builder's foundation plan, which will show tendons. If none of those settle it, a ground-penetrating radar (GPR) scan will.

### What happens if you drill into a post tension slab?

If the bit misses the tendons, nothing. If it nicks or cuts one, the steel can lose its tension, and a severed tendon stores enough energy to be dangerous when it lets go. Engineering firm EVstudio notes that the cost to repair a tendon "generally far exceeds the cost of locating it" before drilling. Repairs range from abandoning the tendon to splicing in new strand with a coupler and re-stressing it, and an engineer should sign off.

### Can you put anchors or bolts into a post tension slab?

Usually, but only shallow ones, placed after the tendons have been located. In houses the tendons commonly run about 48 inches apart in both directions, so the safe approach is a GPR scan, marked tendon lines, and the shortest anchor that does the job. Never core a plumbing or electrical opening without a scan.

### Is a post tension slab better than a rebar slab?

On expansive clay, generally yes for the same thickness of concrete. The Post-Tensioning Institute says the compression from the tendons resists the tension that soil movement puts into the slab and keeps any cracks tight. A well-built rebar slab on well-prepared soil can also perform well; drainage and soil prep matter as much as the steel.

### Can a post tension slab be repaired if it settles?

Yes. Settlement of a post tension slab is usually handled from the outside, with pressed concrete pilings or steel piers under the perimeter beam on the low side, plus drainage fixes. Interior pilings mean cutting through the slab, so the tendons have to be located first. See our [slab foundation repair page](https://foundationrepairbatonrougelouisiana.com/slab-foundation-repair/).

### Are the round patches along my slab edge a problem?

No, they are normal. Each one covers a tendon's stressing anchor. They only become a problem if the grout cracks or falls out and leaves the steel anchor exposed to water. A Texas structural inspector on the InterNACHI forum called exposed caps "not a cosmetic issue" and recommended at least an inch of chloride-free, non-shrink grout over them.

### Do post tension slabs crack?

Yes, small shrinkage cracks are normal in any slab. Post-tensioning is meant to keep them tight. Wide, growing or offset cracks, especially with doors sticking or brick cracking, point to movement worth measuring. Our [crack-size guide](https://foundationrepairbatonrougelouisiana.com/guide/how-big-is-too-big-foundation-crack/) explains where the line is.

About the author

[Jonathan Dyer](https://foundationrepairbatonrougelouisiana.com/authors/jonathan-dyer/)

Structural concrete and steel repair and protection specialist with an industrial background, now writing about slab and pier-and-beam foundation repair on Baton Rouge's expansive clay soils.

[LinkedIn profile](https://www.linkedin.com/in/jonathan-dyer-29779679/) · [All articles by Jonathan Dyer](https://foundationrepairbatonrougelouisiana.com/authors/jonathan-dyer/)

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