Concrete Leveling: Foam, Mudjacking, or Replacement

Driveways, walkways, patios, pool decks, garage floors, and porch slabs all sit on shallow support with no real footing beneath them. That makes them the first thing on a property to reveal a soil problem, and it also makes them comparatively easy to put back, because the job is filling the void underneath rather than reaching a new bearing layer.

In Tallahassee the cause is nearly always water. Roof runoff discharging beside a slab with no gutter extension to catch it. A broken irrigation line. Surface flow crossing a lot during a summer storm. South of the Cody Scarp, on the karst plain, sandy soils carry fines away readily and voids form quickly. North of it, poorly compacted fill under a driveway consolidates and the same drop appears more gradually.

Polyurethane foam injection

The current residential default. Small ports, around five-eighths of an inch, are drilled through the slab. A two-part polymer is injected, expands, fills the void, and then begins to lift the concrete as the pressure builds. The crew watches the slab with a level and stops when it reaches grade.

Its advantages are specific and they matter:

• Weight. Cured foam is a fraction of the weight of a cement slurry, so it adds almost no new load to the same soft soil that allowed the settlement in the first place.
• Speed. It cures within minutes, and the slab is generally back in service the same day.
• Water. It is unaffected by water and does not wash out, which matters in a climate that takes close to fifty-nine inches of rain a year.
• Precision. Injection can be controlled in small increments, so the lift is adjustable rather than all at once.
• Small holes. The patches are noticeable on smooth new concrete and nearly invisible on a weathered driveway.

Mudjacking

The older method, sometimes called slabjacking. A cement-based slurry is pumped under the slab through larger holes, typically an inch and a half to two inches across, filling the void and lifting the concrete.

It is cheaper per cubic foot of material, and under thick, heavy slabs where the additional weight is genuinely not a concern it works perfectly well. The trade-offs are that it is heavy, which is a real drawback on the soft soil that caused the problem; it cures slowly, so the slab is out of service for a day or two; it can be affected by water; and the larger ports leave patches you will see.

Cost, side by side

Job	Typical cost here
A couple of sunken sidewalk panels	$900 to $1,300
One driveway section or approach slab	$1,100 to $1,600
Full driveway apron or patio	$2,000 to $3,500
Garage floor	$2,200 to $3,500
Pool deck or long driveway run	$3,500 to $4,500 and up

Foam prices higher per square foot than mudjacking but uses far less material, so on most residential jobs the totals land closer together than the unit rates suggest. Compare against replacement, which for a typical driveway runs several times these figures before you account for the disruption.

When lifting is the wrong answer

A slab lifts as a unit or not at all. It is a good candidate when it has dropped mostly intact, with a few clean cracks that can be sealed afterwards. It is a poor candidate when it has broken into many small pieces, when the edges are crumbling, or when the surface has spalled through from years of freeze cycles and wear.

That assessment takes about a minute on site and it is visible to anyone standing on the slab. A crew that quotes lifting on concrete that is genuinely finished is doing nobody any favours, and a crew that says replace this rather than lift it is usually giving you the more honest answer even though it is the larger number.

The part that decides whether it lasts

Leveling puts the concrete back. It does nothing whatsoever about why the concrete went down. If a downspout has been discharging beside that driveway for ten years, the same water will undermine the same slab again, and the second visit will feel like the repair failed when in fact the repair worked and the cause was left alone.

So the useful version of this job is nearly always leveling plus a drainage correction: extending the downspout, restoring the fall away from the slab, or intercepting the surface flow that is crossing the lot. Together they cost meaningfully more than leveling alone and considerably less than leveling twice. See drainage and grading.

Reading it as a signal

One last point, and it is the reason this guide sits alongside the structural ones. Flatwork sits far shallower than a house footing, so when it drops it is telling you something about water on that part of the lot before the house has any reason to complain.

A sunken driveway is not evidence that the house is in trouble. It is a reasonably reliable indication of where water is going, and following that information back to its source is free. If the same corner of the property also has the downspout, the answer has arrived without anyone needing to price a pier.