Deep-Dive · Part 3

Slab Lifting: Mudjacking vs. Polyurethane Foam

Deep-dive from How Foundations Get Fixed: Repair Methods in Plain English

A concrete slab that's settled — a garage floor with a sunken section, a driveway panel that's dropped, a front walk that's created a trip hazard, a patio that no longer drains properly — doesn't have to be torn out and replaced. In many cases it can be lifted back toward level by filling the void that opened up under it.

That's what slab lifting does. Two methods do it: mudjacking, which has been around for decades, and polyurethane foam injection, which has become the preferred method for most applications in the last fifteen years. Both work; they work differently and suit different situations.

Same note as the piers article: Precision Remodel refers slab lifting to trusted specialist contractors. This guide gives you the context to evaluate the recommendation and ask the right questions.

What causes slabs to settle

A concrete slab sits on a base layer of compacted soil or gravel. When that base shifts, the slab follows — or in many cases, the slab stays put while the support disappears beneath it, creating a void.

Common causes in Maryland:

Poorly compacted fill under the slab. Garages, additions, and slabs built over excavated and backfilled areas are especially vulnerable. If the fill wasn't properly compacted at the time of pour, it settles over years as it consolidates under load.

Soil erosion from water. Water running under a slab washes fine soil particles away, creating voids. Downspouts that discharge near a slab, poor grading that channels water under edges, and plumbing leaks are all common sources. This is one of the most dramatic void-creation mechanisms — and the most important to address before lifting.

Clay soil shrinkage in dry seasons. Maryland's expansive clay pulls away from slab edges and loses volume under dry conditions, leaving gaps the slab can't bridge.

Freeze-thaw cycling. Ice formation beneath slab edges can lift sections; when the ice thaws, the slab may not return to its original position.

Organic decomposition. Tree roots, old wood forms left in place, and other organic material in the soil can decompose over decades, leaving voids.

Mudjacking: the traditional method

Mudjacking (also called slab jacking or pressure grouting) has been used since the 1930s. The method is simple: a slurry of cement, soil, and water is pumped through holes drilled in the slab, filling the void beneath and pushing the slab upward.

The process:

  1. Holes approximately 1.5–2 inches in diameter are drilled through the slab at strategic locations
  2. The cement slurry is pumped under pressure through the holes
  3. As the slurry fills the void, it pushes the slab upward
  4. When the slab reaches the target elevation, pumping stops
  5. Holes are patched with concrete

Advantages:

Disadvantages:

Polyurethane foam: the modern method

Polyurethane foam injection (also called polyjacking, foam lifting, or PolyLevel) has become the preferred method for most residential slab lifting applications. Two-part polyurethane foam is injected through small holes and expands aggressively to fill the void and lift the slab.

The process:

  1. Small holes — approximately 5/8 inch in diameter — are drilled through the slab
  2. Two-part polyurethane components are injected through a mixing nozzle
  3. The components react and expand into a rigid closed-cell foam, filling the void and pushing the slab up
  4. The operator monitors elevation in real time and stops when the target is reached
  5. Holes are patched; foam reaches full cure within 15–30 minutes

Advantages:

Disadvantages:

Which method is right?

For most Maryland residential applications — garage floors, driveways, walks, patios — polyurethane foam is the better choice for several reasons specific to the local environment:

Maryland's clay soil is already under load from the slab. Adding 100+ pounds per cubic foot of mudjack slurry to soil that already couldn't support the slab adds weight and can cause new settlement adjacent to the lifted area. Foam adds almost none.

Water-caused erosion is the most common void-creation mechanism in Maryland (rain, poor drainage, downspout discharge). A fill material that can wash out (mudjacking slurry) is a poor match for conditions likely to re-expose the slab to water. Foam doesn't wash out.

The only clear case for mudjacking is cost sensitivity on a job where the slab conditions are good (no ongoing water issue, stable soil), the hole size doesn't matter, and cure time isn't a factor.

Neither method is appropriate when:

What slab lifting cannot do

It cannot repair slab damage. Cracks in the slab, spalling, scaling, or structural deterioration aren't addressed by lifting — only the elevation problem is.

It cannot fix the cause. A slab lifted without fixing the drainage problem, plumbing leak, or other cause of the void will re-settle. The fix must include addressing the cause.

It cannot work on badly deteriorated slabs. If the concrete itself is too far gone — brittle, crumbling, cracked into many pieces — it can't be lifted; it needs to be replaced.

It's not for heaved slabs. Heave (a slab pushed up by expanding soil) is the opposite problem. Foam or mudjacking won't push a heaved slab back down — that requires waiting for the soil to dry and contract, or in severe cases, removing the slab, addressing the soil, and repouring.

Realistic cost expectations in Maryland

Slab lifting costs vary more by job geometry than by method, because both methods price primarily on the volume of material used and the area and number of holes drilled.

General ranges:

Polyurethane typically costs 10–30% more than mudjacking for equivalent scope, reflecting higher material costs. On most jobs, the difference is a few hundred dollars — generally worth it for the reasons discussed above.

Compare slab lifting to replacement: tearing out and repouring a 2-car garage floor in Maryland can cost $4,000–$10,000+. Lifting the settled section for $1,500–$2,500 is usually the better economic choice if the concrete itself is in decent condition.

Questions to ask a slab lifting contractor

The one-page summary

When to Get Eyes on It

Is Lifting the Right Fix
for Your Slab?

If you have a settled slab — a section that's dropped, a trip hazard that's developed, a garage floor that slopes — the first question is whether lifting is the right approach for your specific situation.

On-site visual assessments start at $300 — and that fee is credited back to any repair work if you choose to work with us, so the honest professional read costs you nothing when we're the right fit. Written reports or structural engineer coordination scope separately with cost given upfront.

Precision Remodel provides the diagnostic assessment that frames that decision — what caused the void, whether the slab is in adequate condition for lifting, whether the water source has been addressed, and what you should expect from the repair. We refer the actual lifting work to trusted Maryland specialists. When you're comparing slab lifting bids, we can help you read them.

Request a Foundation Assessment Call 443-761-9209

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Common Questions

Frequently Asked Questions

Slab lifting fills the void that has opened under a settled concrete slab and uses that fill to push the slab back toward its original elevation. Two methods exist: mudjacking, which pumps a cement slurry under the slab, and polyurethane foam injection, which uses expanding foam. Both fill the void from below; the material's expansion lifts the slab without tearing it out.

Mudjacking uses a heavy cement-and-soil slurry pumped through large holes (1.5–2 inches). Polyurethane foam expands through small holes (5/8 inch), cures in minutes, weighs almost nothing, and doesn't wash out the way slurry can. Foam is generally preferred for Maryland applications because of lighter load on already-compromised soil and better performance in wet conditions.

Roughly $500–$1,500 for small jobs, $1,500–$3,500 for medium jobs (a garage section or patio), and $3,000–$6,000+ for large jobs. Polyurethane typically costs 10–30% more than mudjacking for equivalent work. Compared to tearing out and repouring concrete ($4,000–$10,000+ for a garage floor), lifting is usually significantly less expensive if the concrete itself is in decent condition.

No — it's appropriate for slabs that have settled (dropped) due to voids forming beneath them, where the concrete itself is structurally sound. It doesn't work on heaved slabs (pushed up), badly deteriorated concrete that's crumbling or cracked through, or foundation footings that have settled (that requires piering). And it must be paired with fixing the cause of the void — otherwise the slab will re-settle.

Polyurethane foam jobs can often be completed in a few hours for a typical residential job, with the slab ready for light traffic within 30–60 minutes. Mudjacking takes longer, with a cure period of several hours to a day before loading. Either method is dramatically faster than tear-out and replacement, which requires concrete cure time of several days before loading.