Here's something you'll hear from us more often than you might expect: "Don't lift that one."
A lift that shouldn't have happened costs you money and leaves you with a level slab that keeps cracking, rocking, or flaking. We'd rather say so up front, keep your trust, and put our effort into the slabs that are worth saving.
This guide lays out the scale we use to judge a slab from photos, the borderline cases that could go either way, the mixed plans that save the good concrete, and how to take pictures that make the call easy.
What a Slab Needs to Be Liftable
Foam lifting works from underneath. We inject high-density foam through 5/8" holes, about the size of a dime. It fills the voids first, then pushes up on the slab in small, controlled increments. For that to work, a slab has to pass four tests:
- 1It went down, not upFoam can only raise concrete, never lower it.
- 2It's worth keepingIf the surface is falling apart, a level version of it is still falling apart.
- 3It gives the foam something to push againstFoam follows the easiest path. Wide-open cracks and crumbling concrete give it an easy path to the surface, so it escapes instead of lifting.
- 4It moves as a unitPushing up under one area should raise a whole piece of concrete, the way lifting one side of a tabletop raises the entire top. A slab broken into many small pieces rises one piece at a time, and each one tips its own way.
Pass all four and it's almost certainly a lifting job. Fail one and the details decide.
The 1–5 Damage Scale
This is our working scale. It's a judgment tool, not an industry standard, but it matches how slabs actually behave when they're lifted.
| Grade | What it looks like | How to spot it in a photo | Liftable? | Usual plan |
|---|---|---|---|---|
| 1. Sound | Sunk or tipped, in one piece. Maybe a few hairline cracks. Surface tight | No crack runs all the way across. Surface matches the neighboring slabs | Yes | Lift, then seal the joints |
| 2. Cracked, still one unit | One tight crack, or a cracked corner that's still snug | A single tight crack, both sides at the same height, sharp crack edges | Yes, usually | Lift, then caulk the crack |
| 3. Two or three big pieces | A through-crack with a step in it, or two cracks making three large pieces | Every piece is a big share of the slab, and crack edges are still sharp | Often, case by case | Lift each piece to match, then caulk the cracks |
| 4. Breaking up | Four or more pieces, crumbling crack edges, or deep flaking over most of the surface | A web of cracks, small pieces, rounded or missing crack edges, stones standing out | Usually not by itself | Replace this slab, often while lifting its neighbors |
| 5. Failing | Rubble, missing chunks, holes, rusting steel, crumbling throughout | Soil or rebar showing, pieces shifted apart | No | Replace |
How to count pieces from a photo: trace each crack with your finger. A piece only counts if cracks cut it off completely, from edge to edge or crack to crack. A crack that stops partway doesn't create a new piece, and a tight, level crack that runs all the way across usually still behaves like one piece until it opens up or steps.
Borderline Cases, Explained
One clean crack straight through
Often still liftable. One crack splits a slab into two big halves, and each half is still stiff on its own. We set holes on both sides of the crack and raise the halves together so the crack comes back to flush. You'll still see the crack, and it should be sealed afterward so water doesn't run down it into the base.
What tips it toward "no": crack edges that are crumbling, a crack open wide enough to swallow a finger, or one half that rocks freely when you step on it.
A snapped corner
Corner breaks are common on driveways and aprons where tires roll over the edge, often right above a void. If the corner piece is big and tight against the rest of the slab, it usually lifts with it. If it's small, loose, and rocking, it may not hold pressure, and a concrete contractor may need to cut it out and repair it. That isn't work we do, but your quote will say so.
Four or more pieces
Usually not liftable. With four pieces, each needs its own holes, each tips its own way, and every crack between them is an exit for the foam. You end up with a roughly level patchwork that keeps shifting, with crack lines that let water straight into the base. On the rare back walk where looks don't matter and the only goal is removing a trip edge, a lift can buy some time, but we'd call it what it is: a stopgap.
In one piece, but the surface is shot
Scaling, popouts, and spalling are surface damage. They ride along with the slab, so lifting won't make them better or worse. How deep it goes decides the plan:
- Light scaling (rough patches, no stones showing): lift it if it's sunk, then clean it and apply a penetrating silane or siloxane sealer, the type that best resists further salt scaling.
- Moderate scaling (stones showing, roughly 1/8" to 3/8" of surface gone): lift if the height or slope is the real problem, and know the look stays. Some homeowners follow up with a bonded resurfacing from a concrete contractor, which is only as good as the sound concrete under it.
- Severe scaling (stones standing out across most of the slab): usually a replacement candidate, since you'd be paying to lift concrete you'll soon replace.
Our spalling guide helps you tell these apart, and freeze-thaw concrete damage covers the deeper kinds.
Rust stains, or a web of fine cracks along the joints
Rust-colored stains, or cracks running in straight lines where steel would sit, can mean reinforcing is rusting and pushing the concrete apart. Closely spaced cracks that run along joints and edges, often with dark staining, can be D-cracking, where the stone inside the concrete breaks down from freeze-thaw. Both mean the concrete is failing from the inside. Leveling it doesn't stop that. Replace.
Heaved, not sunk
No lifting method can push concrete down. If roots or frost shoved a slab up, the options are raising the slabs around it to ease the edge (fine on walks, rarely fine on patios and aprons), grinding a small lip, or replacing the high slab. Make sure it really is heave first: a slab that's high in February may settle back by late May. See frost heave vs. settling and tree roots lifting concrete.
Replacement timing is typical; a contractor's schedule and the weather can stretch it. New-concrete cure times from Concrete Network.
Mixed Plans: Some of Each
Most properties aren't all one grade. A driveway might have one shattered slab and four that simply sank. The smart move is often to spend replacement money only where it's needed.
| Situation | Plan | Who does what |
|---|---|---|
| One slab shattered, neighbors sunk but sound | Replace the bad slab, lift the rest | A concrete contractor replaces. We lift and seal the joints |
| Sound slab, tired surface | Lift, then clean and seal | We can handle all of it, in order |
| Height is fine, surface is the problem | Resurface or replace | A concrete contractor. No lift needed |
| One heaved slab in a run of sidewalk | Lift the neighbors to blend it | Usually us |
| Moderate scaling, slab tipped toward the house | Lift to fix the slope, resurface later if you want new looks | We lift. A concrete contractor resurfaces |
Worked example: a six-slab driveway
Say your driveway is six slabs, each 10 by 12 feet, 720 square feet in all. The slab at the apron is in five pieces. Two others sank but are in one piece. Three are fine.
- Replace everything: at the roughly $8–$15 per square foot that driveway replacement has run in recent Green Bay data, that's about $5,760–$10,800.
- Replace one, lift two: replacing 120 square feet works out to about $960–$1,800 at the same rate, though small jobs often cost more per foot or carry a minimum. The two sunken slabs get lifted, typically for a fraction of what replacing them would cost, and the three good slabs stay put.
The mixed plan keeps 600 square feet of concrete you already paid for.
Order matters
When a replacement and a lift happen side by side, agree on the order before anyone starts. If the new slab goes in first, ask the crew not to pin (dowel) it into slabs that still need lifting, and let it cure before the lift. If the lift goes first, the replacement crew gets the right heights to pour to. Either way, the new slab and the lifted ones need to meet flush and drain the same direction.
Lift, then seal
On a combined job, the order is: clean, let it dry, lift, patch the holes, caulk the joints, then apply penetrating sealer once the caulk has cured. If you plan to have a resurfacing overlay put down after a lift, tell us before we caulk, since some overlay products don't bond over polyurethane sealant. See clean and seal concrete and pouring over existing concrete.
How to Photograph Damage So We Can Judge It
Most bad calls from photos start with bad photos: a zoomed-in shot from the porch, at noon, with snow in the cracks. These eight shots fix that.
| Shot | How to take it | What it tells us |
|---|---|---|
| 1. The wide shot | Step back far enough to get the slab and its neighbors, from the low end | How it sits against the house, garage, and street |
| 2. The overhead | Hold the phone straight down from as high as you can reach, or stand on a step stool | How many pieces. This is the shot that grades the slab |
| 3. The step | Stand a tape measure at the lowest edge or crack | How far it has to come up |
| 4. The crack width | Lay the tape across the widest crack, close up | Whether the crack can hold pressure |
| 5. The crack edges | Close-up of a crack with a coin beside it | Sharp edges are good news. Rounded or crumbling edges aren't |
| 6. The low-sun shot | Early morning or evening, with the sun low and off to the side | Long shadows show how deep the flaking goes |
| 7. The wet-dry shot | Hose the slab, wait until the surface starts drying, then shoot | Cracks hold water and stay dark, so hidden ones show up |
| 8. The rock-test video | Film while you step on each piece and corner | Rocking pieces and loose corners |
Two extras help: a photo of the nearest downspout, and a note about anything recent nearby, such as sewer work, a removed tree, or an addition.
Skip shots with snow, leaves, or puddles covering the slab, midday sun straight overhead (it flattens texture), and zooming from far away instead of walking closer.
What a "No" From Us Looks Like
When a slab isn't a lifting job, you won't get a vague brush-off. You'll get:
- Which slabs, and why, in plain terms, using the grades above.
- Who to call instead: a concrete contractor for replacement or resurfacing, a plumber for a leaking pipe, an arborist for roots, or a foundation specialist for basement walls.
- What's still worth lifting, so you only replace what's truly done.
- What to ask the replacement contractor so the new slab doesn't sink like the old one. Our concrete replacement questions are a good start.
We don't do replacement, resurfacing, or foundation work, so there's nothing in it for us when we send you elsewhere.