Post-Tension Slabs in Houston: Cables, Tendons and Repair

What's inside a post-tension slab

The Foundation Performance Association (FPA), a Houston-based nonprofit professional organization, describes the tendons in a typical home slab as 1/2-inch, seven-wire steel strands with a yield strength of 270 ksi. Each one is stretched by a hydraulic jack and locked at the slab edge with wedge-type anchors. Home slabs normally use unbonded tendons: the steel is coated with corrosion-inhibiting grease and wrapped in plastic sheathing, so it grips the concrete only at the anchored ends. Tendons are typically fully stressed and anchored 3 to 10 days after the concrete is placed (FPA-SC-01-0, §5.2.1, 2004, checked 2026-10-17).

Why so many Houston homes have a post-tension foundation

The same paper says post-tensioned reinforcing "has become the norm for residential slabs in most Texas metropolitan areas" (FPA-SC-01-0, 2004, checked 2026-10-17).

The Post-Tensioning Institute, the industry's trade association, says post-tensioned slabs-on-ground are a cost-efficient solution for homes on shrink-swell soils. Among the advantages it lists: less concrete and steel for the same structural capacity, a stiffer slab that better resists bending from differential soil movement, less cracking with any cracks kept tight, and often faster installation (Post-Tensioning Institute, Slab-on-Ground, industry association, checked 2026-10-17). Those are the industry's own claims. The Foundation Performance Association's comparison table lists similar advantages (lower cost than rebar, faster construction, and control of curing and shrinkage cracks once the tendons are stressed), alongside the drawbacks below (FPA-SC-01-0, Table 5.2.1, 2004, checked 2026-10-17).

The association's 2005 homebuyers' guide says the foundations of most new homes are post-tensioned, "as this is the most economical method of foundation construction" (FPA-SC-06-0, Homebuyers' Guide for Foundation Evaluation, 2005, checked 2026-10-13). That doesn't tell you about a particular house. The same guide suggests requesting copies of the construction drawings and the soil report.

Before you drill, cut or core

Rebar is "passive" reinforcement that carries no force until the concrete deflects and cracks under load. The association calls post-tensioned tendons "active" reinforcing because they are prestressed and carry tensile force even when no loads are applied (FPA-SC-01-0, §5.2.2, 2004, checked 2026-10-17).

The association lists this as a drawback of the system: "Making penetrations into slab can be hazardous due to presence of tensioned cables" (FPA-SC-01-0, Table 5.2.1, 2004, checked 2026-10-17). Don't cut, core or drill into a post-tension slab yourself. Hire a professional engineer before anyone cuts, cores or drills into it, for plumbing, a floor anchor or anything else. This page gives no do-it-yourself steps.

Warning signs at the slab edge

The tendon end anchorages are "highly stressed critical elements" located on the outside face of the foundation, where exposed strand ends and anchors "can be susceptible to corrosion." The association also says these slabs can suffer blowouts, a sudden bursting failure of the concrete during or after stressing, and that a failed tendon, anchorage or blowout needs extra work to repair (FPA-SC-01-0, Table 5.2.1, 2004, checked 2026-10-17). Don't pry at, cut or try to fix exposed or corroded cable ends or broken concrete at the slab edge yourself; the anchorages are highly stressed. Hire a professional engineer to look at them. Other cracks are covered on our foundation crack repair page and the wider checklist is on signs of foundation problems.

How engineers test tendons

Lift-off test. A calibrated hydraulic ram grips the exposed end of a tendon and pulls until the anchor wedges release, measuring the force still in the cable. The association warns that a strand can fail during the test, possibly turning the far end of the tendon into "a projectile," that the anchor and strand tail should be checked for corrosion first, and that only properly trained personnel should run it (FPA-SC-02-0, Test Methods for Evaluating Existing Foundations, §2.19, 2010, checked 2026-10-17).

Screwdriver penetration test. The association describes a test in which concrete is removed to expose part of a tendon away from its anchors, to help tell whether the tendon has been stressed, cut or broken. It says the test is most useful for spotting a tendon with no tension, can't readily tell full tension from partial tension, and that tendons may be damaged while the concrete is removed (FPA-SC-02-0, §2.20, 2010, checked 2026-10-17).

Both tests are for trained professionals; don't try them yourself. Our foundation inspection guide explains what an engineer's visit covers more broadly.

Post-tension slab repair: re-stressing and other fixes

The Texas Section of the American Society of Civil Engineers says stressing relaxed or inadequately stressed post-tensioned tendons may be applicable when tests show tendon forces below those specified in the original design or by applicable authority. It says stressing may restore the slab's residual prestress and should be done after any elevation adjustments and epoxy crack injection (ASCE Texas Section, Guidelines for the Evaluation and Repair of Residential Foundations, v3, §7.4.3.4, 2022, checked 2026-10-13). Leveling and pier work on slabs are covered on slab foundation repair and helical piers; if the house seems to be settling, see sinking foundation. For published price ranges, see our cost page.

Quote requests are coming soon. For now, call (832) 646-1494 or email [email protected].

When quote requests open, the contractor we refer you to will pay us for each referral; you pay us nothing. We're not a contractor.

Buying a newer home on a post-tension slab

The association's homebuyers' guide suggests asking for the construction schedule, or a letter, showing when the foundation was cast and when the cables were stressed, and, for post-tensioned slabs, checking that stressing happened within 3 to 10 days of the pour (FPA-SC-06-0, Homebuyers' Guide for Foundation Evaluation, 2005, checked 2026-10-13). Buying or selling more generally is covered on buying or selling a house with foundation problems. Tips on comparing companies are on how to choose a foundation repair company.

Permits in the City of Houston

The Houston Permitting Center says a residential repairs permit is required for repairs that involve the replacement or repair of existing structural members and other building elements (Houston Permitting Center, Structural Inspections, checked 2026-10-17). Outside Houston, ask your city.