# Post-Tension Slabs and Repair Limits

> How post-tension slabs work, what cracks and movement mean, and when repair or replacement is the practical limit.

Canonical: https://foundationrepairlab.com/post-tension-slab/

Last updated: 2026-11-09

## What a Post-Tension Slab Is

A post-tension slab is a concrete foundation reinforced with steel tendons run through ducts inside the slab. After the concrete reaches design strength, the tendons are pulled tight and anchored at the edges, placing the slab in compression. That compression helps the concrete resist cracking and allows thinner slabs to span longer distances than conventional reinforced concrete.

The key difference from standard rebar is timing and force. Rebar sits passively in the concrete and only engages after the slab cracks and bends. Post-tensioning actively squeezes the concrete before loads are applied. For homeowners, that means the slab can perform well under normal soil movement, but it also means the tendons are a critical component. If a tendon is cut, corroded, or anchor-damaged, the slab loses part of its design strength. Repairing around post-tension tendons requires knowing where they are before any cutting, coring, or excavation begins.

## How to Measure the Slab First

Before choosing a repair method, measure what is actually happening. Foundation Repair Lab follows a numbers-first sequence: crack width and displacement, pier count, depth to bearing, then unit price.

Start with crack width. Use a crack comparator or feeler gauge, not a ruler held by eye. Cracks up to 1/16 inch are generally cosmetic. Cracks at or near 1/8 inch enter the watch category, meaning they should be marked, dated, and rechecked over several months. Cracks wider than that, or cracks that show vertical displacement where one side is higher than the other, warrant closer inspection.

Measure floor levelness across the slab. A level or elevation survey can show whether the slab is tilting or settling in localized areas. Note the location of interior walls, plumbing penetrations, and any prior patching. If you see cracks radiating from corners or near slab edges, that can indicate edge bearing loss rather than center-span flexing.

For post-tension slabs specifically, ask whether as-built drawings are available. They show tendon layouts and anchor locations. If drawings do not exist, a professional may use ground-penetrating radar or cover meters to locate tendons before any invasive work. This step matters because striking a tendon during a repair can release tension and damage the slab.

## Common Repair Methods and Costs

Repair options for post-tension slabs fall into slab lifting, crack repair, and structural support. Each has a typical cost range and a practical limit.

Slab lifting fills voids under the slab to restore support. Mudjacking pumps a cementitious grout under pressure and costs about $3 to $8 per square foot. Polyurethane foam injection costs about $5 to $15 per square foot and is lighter, but it is not a structural fix for tendon problems. General slab lifting is often priced around $3 to $12 per square foot depending on access and material. For a 1,500-square-foot home, mudjacking at $5 per square foot would be roughly $7,500, while poly foam at $10 per square foot would be about $15,000. These are estimates, and actual prices vary by region and site conditions.

Crack repair for narrow, non-structural cracks can involve epoxy injection or surface sealing. Carbon fiber straps are sometimes used on foundation walls, not typically on slab surfaces, and cost roughly $400 to $1,200 per strap when applied to vertical foundation elements.

When settlement is the issue, piers transfer load to deeper bearing soil. Push piers cost about $1,000 to $3,000 each, and helical piers cost about $700 to $2,500 each. A full pier job often runs $6,000 to $30,000 depending on pier count and depth. For example, eight helical piers at $1,500 each equals $12,000 in materials and installation before engineering or permits. Depth to bearing determines pier length, and longer piers increase cost.

Engineer inspections typically cost $400 to $1,500. That inspection fee is separate from repair work and is often money well spent on a post-tension slab because the engineer can confirm whether cracking is related to tendon performance, soil movement, or both.

## Repair Limits: When to Stop and Replace

Every repair method has a limit. For post-tension slabs, the limit is usually tied to tendon integrity and the extent of slab deterioration.

If tendons are broken or anchors are failed, the slab may not be able to carry its design load even after piers are installed. Piers support the slab from below, but they do not replace the internal compression provided by intact tendons. If a large portion of the tendon system is compromised, adding piers may level the slab temporarily without restoring the original structural system.

A common rule of thumb in foundation evaluation is that replacement becomes a serious consideration when roughly one-third of the structural system has failed. That is not a code threshold; it is a practical decision point. If repair costs approach replacement costs, or if repeated repairs are needed in different areas, replacement may be the more rational long-term choice.

Replacement costs are significant. Full slab replacement is estimated at $40,000 to $150,000 depending on home size, access, and local labor rates. Major repairs fall in the $20,000 to $40,000 range, while average repairs are typically $4,000 to $15,000. Restoration work, such as cosmetic crack sealing or minor leveling, often runs 10 to 25 percent of structural repair costs.

Wall movement is another boundary. If foundation walls supporting the slab show movement beyond 2 inches, the wall itself may need stabilization or replacement before slab repair is meaningful. Wall anchors cost about $500 to $1,500 each when wall stabilization is required.

## What Not to Do on a Post-Tension Slab

Do not cut, core, or drill into a post-tension slab without first confirming tendon locations. Tendons are under high tension, and striking one can cause sudden release, injury, and structural damage. Do not assume that all cracks in a post-tension slab are structural. Many are shrinkage cracks or cosmetic settlement marks that do not threaten the home.

Do not rely on slab lifting alone to fix tendon damage. Lifting restores support beneath the slab but does not repair broken tendons inside it. Do not accept a repair proposal that skips an engineer’s inspection on a post-tension foundation. The inspection cost of $400 to $1,500 is small compared with the risk of misdiagnosing the problem.

Permits vary by city and county and typically take 1 to 3 weeks to process. Inspection lead time is usually 1 to 2 weeks. Factor that into project timing before signing a contract.

## Warranty and Long-Term Expectations

Pier warranties are often described as lifetime and transferable, though transfer fees typically run $100 to $500. A transferable warranty can matter if you sell the home, but read the terms carefully. Coverage usually applies to the pier itself, not to future slab cracking elsewhere.

Mudjacking repairs generally last 5 to 15 years before soil conditions may require attention again. Poly foam longevity depends on soil chemistry and drainage, and it is not a substitute for structural bearing where the soil cannot support the load.

If you are buying a home with a post-tension slab, request the as-built drawings and any prior repair records. Ask whether tendons were ever cut during previous plumbing or HVAC work. A slab with documented tendon damage should be evaluated by an engineer before purchase.

## Deciding Between Repair and Replacement

The decision sequence is measure, then method, then price. First, document crack width, displacement, and elevation changes. Second, identify whether the issue is soil support, tendon damage, or wall movement. Third, compare repair cost against replacement cost using the ranges above.

If cracks are under 1/8 inch and the slab is reasonably level, monitoring may be the only action needed. If localized settlement is causing cracks and door framing issues, piers or slab lifting may be appropriate. If tendon damage is widespread or repair costs approach one-third of replacement value, replacement deserves serious consideration.

Foundation Repair Lab does not endorse specific contractors. Get at least two inspections, confirm tendon locations, and compare written estimates that list pier count, depth to bearing, and unit price. That numbers-first approach protects you from paying for a method your slab does not need.

[Learn more about foundation repair costs](https://foundationrepairlab.com/foundation-repair-cost/)

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[Review foundation crack repair cost details](https://foundationrepairlab.com/foundation-crack-repair-cost/)