How Post-Tension Slabs Work
Quick Answer: Houston slabs often use ‘Post-Tension’ cables (steel tendons under high tension) instead of rebar. If water enters the cable sheath (via a ‘pop-out’ or crack), the cable corrodes and can snap with explosive force, compromising the home’s structural integrity. Signs include rusty cable ends on the foundation perimeter or localized heaving. Repair involves re-tensioning and epoxy encapsulation.
Key Takeaways
- Cables are under 33,000 lbs of tension.
- Rusty ends = Sheath breach.
- Snapped cables require surgical splicing.
Understanding the anatomy of your foundation is critical for Houston homeowners. Unlike traditional reinforced concrete, post-tension slabs rely on high-strength steel tendons that are stretched tight after the concrete has cured. This internal pressure allows the slab to withstand the volatile movements of local clay soils.
“That rusty wire isn’t trash; it’s holding your house together. If a post-tension cable snaps, your foundation loses its spine.”
— Structural Forensic Engineer
Identifying ‘Tendon Pop-Outs’
Corrosion is a silent threat. When the plastic sheathing around a cable is compromised, moisture meets the high-tension steel. This leads to oxidation, expansion, and eventually, failure. Look for the following symptoms on your foundation perimeter:
| Symptom | Cause | Urgency |
|---|---|---|
| Rusty Cable End | Sheath Failure | High |
| Loud ‘Bang’ | Cable Snap | Critical |
| Slab Cracking | Loss of Tension | High |
The Splicing and Re-Tensioning Process
Repairing a post-tension system is a high-stakes engineering task. You cannot simply “patch” a snapped cable. The process involves excavating the anchor points, removing the corroded section of the tendon, and installing a specialized splice. Once the new segment is in place, hydraulic jacks are used to re-apply the thousands of pounds of force necessary to restore the slab’s structural capacity.
Frequently Asked Questions
What happens if a post tension cable breaks?
The foundation loses structural rigidity, leading to severe cracking and instability. It can also cause physical injury if it snaps explosively.
Is your slab at risk?
Don’t ignore exposed wires. Schedule a professional assessment today.