You ask three companies to "level" the garage approach that sank last spring. Now meltwater runs at the garage door instead of away from it.
The quotes come back nowhere close. One says drill and inject. One says grind and bevel. One says prime and pour.
Those aren't three prices for one job. They're three different jobs that answer to the same word, and only one deals with the water at your door.
First, "Level" Usually Isn't the Goal
- Level means horizontal. Set a marble down and it stays put.
- Flat means no humps, dips, or lips, whether the surface is horizontal or sloped.
Outdoor concrete should be flat but almost never level, because it has to shed water. The International Residential Code, a national model code, calls for paved surfaces within 10 feet of a house to fall away at least 2 percent. That's about 1/4 inch per foot, or roughly an inch of drop across a 4-foot level.
Indoors, flatness is what counts. The tile installation standard (ANSI A108.02) wants the floor under typical tile within 1/4 inch over 10 feet, and within 1/8 inch over 10 feet for tile with any edge 15 inches or longer.
So when someone offers to "level" your patio, ask: level, or back to the right slope?
Five Jobs That All Get Called "Leveling"
| Job | Works from | Moves the slab? | What happens to height |
|---|---|---|---|
| Slab lifting | Underneath | Yes, up only | The whole slab rises |
| Self-leveling underlayment | On top | No | Adds a thin layer |
| Grinding | The high edge | No | Removes concrete |
| Resurfacing / overlay | On top | No | Adds a thin layer |
| Replacement | Everything | It's a new slab | Starts over |
1. Slab Lifting: Raising the Slab From Below
What it physically does: A contractor pumps material into the empty or soft space under a sunken slab until the slab is supported, then keeps pumping until it rises back to height. You keep your concrete. Only what's under it changes.
What it fixes: Slabs that went down. A lip at a joint, a garage approach tipped toward the door, a patio draining at the foundation, a walk that rocks.
What it can't do: Lower a slab, put broken-up concrete back together, or change the surface. Scaling, stains, and cracks ride along.
Three methods, with overlapping names:
- Polyjacking (foam lifting): high-density structural polyurethane foam injected through 5/8" holes, about the size of a dime. It's the only method we use.
- Mudjacking: a cement and soil or sand slurry pumped through holes typically 1–2" across. Plenty of people call this slabjacking, though some contractors use that word for any lifting method.
- Stone slurry grout: a crushed limestone slurry pumped through holes of about 1".
We compare them head to head in how concrete lifting works and foam vs. mudjacking.
Ask so you know it's really a lift:
- "What goes under the slab, and what size are the holes?"
- "Which slabs are you raising, and to what?" "To match the garage floor and fall away from the door" is a lift answer.
- "What happens if a slab cracks or won't move?"
- "When can I drive on it, and what does your warranty cover?"
2. Self-Leveling Underlayment: Smoothing an Indoor Floor
What it physically does: A runny, cement-based mix gets poured over a primed slab and flows out flat on its own. One contractor-grade product we checked goes 1/8" to 2" in a single pour, is labeled for interior use only, isn't meant to be a wear surface, and gives you about 15–20 minutes of working time at 70°F.
What it fixes: A stable indoor floor that's too wavy for tile or plank. Old patches, rough transitions, a dip where a wall used to stand.
What it can't do: Raise a sunken slab (the void stays), stop a moving crack (that data sheet says not to pour over one), hold up outdoors, or serve as the finished floor. It also seeks level by design, which is perfect under tile and wrong for an apron that needs to shed water.
A Wisconsin trap: a garage counts as indoors on paper, but a Green Bay garage gets salt slush, freezing temperatures, and tire traffic. That's not the dry interior floor these products are typically labeled for.
Ask so you know what you're getting:
- "Is this product rated for this location?" Interior dry area, garage, and exterior are three different answers.
- "What's the thinnest it can go?" Feather edges at doors and drains are where thin layers break.
- "What goes on top of it?" If the answer is "nothing," ask why an underlayment is being sold as a floor.
- "Is the slab still moving?" If it rocks or the dip keeps growing, it needs to come up first.
More in self-leveling concrete problems.
3. Grinding: Taking Down the High Side
What it physically does: A diamond grinder or specialty saw removes concrete from the high edge or spot, turning a sharp lip into a short ramp. You'll also hear shaving, beveling, or trip-hazard cutting.
What it fixes: Small lips on a walk that's otherwise solid, ridges on a floor before flooring goes down, and a heaved edge that lifting can't bring down. On accessible routes, ADA standards allow a 1/4" to 1/2" edge only if it's beveled no steeper than 1:2, so grinding a bevel is a standard fix for small lips.
What it can't do: Raise anything or fill a void. If the low slab is still sinking, the lip comes back. A big offset becomes a long, lighter-colored ground strip that can expose the stone inside the concrete. And don't grind a raised edge in March: if frost pushed it up, it may settle back by June. See frost heave vs. settling.
Ask so you know what you're getting:
- "Which slab are you grinding, and how long will the ground area be?"
- "How do you control the dust?" Grinding concrete throws silica dust. Federal OSHA construction rules list two setups for handheld grinders: a built-in water feed (outdoors only) or a shroud hooked to a dust collector. A crew with neither is a red flag.
- "Will the lip come back?" If the low slab sank, the honest answer is "maybe."
4. Resurfacing and Overlays: A New Top on an Old Slab
What it physically does: A thin layer of polymer-modified cement gets bonded to the existing slab. Common bagged resurfacers run from a feather edge to about 1/2".
What it fixes: A slab that sits where it belongs but has a worn, scaled, or patchy surface.
What it can't do: Fix sinking or rocking, because the overlay follows the slab. Make up a big drop. Stop old cracks from coming back: one resurfacer data sheet we checked says reflective cracking can't be completely prevented and is more likely where the slab has settled. That same sheet says not to apply over painted or sealed concrete.
Wisconsin reality: water that gets under a thin layer freezes and pries it up, and salt attacks the surface, which is all an overlay is. The data sheets we checked want air and concrete at 45–50°F or warmer. Green Bay's normal overnight lows don't clear 50°F until June and slide back toward it by September, so outdoor resurfacing here is a summer job.
Ask so you know what you're getting:
- "Is it rated for exterior freeze-thaw and deicers?"
- "How will you prep?" Data sheets call for high-pressure washing or mechanical roughening, then dampening. A quick rinse isn't prep.
- "How will the joints be carried through, and how much height does it add at the garage door?"
More in pouring over existing concrete.
5. Replacement: Starting Over
What it physically does: The old slab gets saw-cut, broken out, and hauled away. The base gets fixed (or should), then new air-entrained concrete is formed and poured.
What it fixes: Concrete broken into many pieces or crumbling, a slab built with the wrong slope, a heaved slab you can't live with, a new layout.
What it can't do: Fix the soil and water on its own (a new slab on the same washed-out base can sink too), match the old concrete's color, or be used right away. Plan on about a week before you park on it and no deicers its first winter.
Ask: "Why did the old one fail, and what are you doing differently?" Then work through our questions to ask before replacing concrete.
Same Problem, Four Quotes: A Worked Example
Back to that garage approach, with a fourth quote added for replacement. Say it runs 10 feet from the garage door to the next joint, and the garage end has dropped 1-1/4" below the garage floor. To hit the 2 percent target, it should fall about 2-1/2" away from the garage over those 10 feet.
| Quote | What it would do | Water drains away afterward? |
|---|---|---|
| Self-leveling overlay | Fill the low end up to the garage floor, feathering out to nothing | No. It flows level, the void stays, and an interior product won't last on an apron |
| Grinding | Grind the garage floor edge into a ramp down to the sunken slab | No. You'd cut into good concrete, and water still runs at the door |
| Foam lifting | Raise the slab to meet the garage floor and pitch it away, filling the void | Yes |
| Replacement | Pour a new slab at the right pitch | Yes, if the base gets fixed too |
Two of the four quotes solve a different problem. Compare the other two.
Read the Quote: Words That Tell You Which Job It Is
| If the quote says... | You're probably looking at... | Confirm |
|---|---|---|
| Drill, inject, foam, polyurethane, pounds of material | Foam lifting | Hole size, which slabs, target height and slope |
| Pump, slurry, grout, mudjack, slabjack | Mudjacking or stone slurry | Material, hole size, wait before driving |
| Grind, shave, bevel, trip-hazard removal | Grinding | Which slab, size of the ground area, dust control |
| Prime, pour, SLU, underlayment | Self-leveling underlayment | Interior or exterior rating, what goes on top |
| Resurface, overlay, skim coat, microtopping | Resurfacing | Thickness, exterior rating, joints |
| Saw-cut, demo, haul-off, R&R, forms, base | Replacement | Thickness, base prep, air entrainment, permit |
| Patch, ramp, taper, fill the lip | Patch mortar troweled over the edge | Expect it to break loose outdoors |
| Just "level" | Any of the above | Ask which one |
If Your Problem Is..., You Need...
| If your problem is... | You need... | Not... |
|---|---|---|
| One slab dropped at a joint | Lifting | A patch ramp or outdoor self-leveler |
| A slab that rocks or sounds hollow | Lifting, which fills the void | An overlay, which bridges over it |
| Garage approach or patio tipped toward the house | Lifting to restore the pitch | Self-leveler, grinding, or resurfacing |
| Crack with one side higher | Lift the low side, then seal the crack | Caulk alone |
| A small lip on a solid walk that isn't moving | Grinding, or lifting the low side | Replacement |
| Slab pushed up by tree roots | Grind a small lip, lift the neighbors to blend it, or replace | Lifting the high slab, which can't lower it |
| Wavy indoor floor getting tile or plank | Self-leveling underlayment, high spots ground | Lifting, unless the slab sank |
| Scaled surface on a slab that sits right | Cleaning and a penetrating sealer; resurfacing if looks matter | Lifting |
| Pitted, stained garage floor that isn't moving | A garage floor coating, with crack repair in the prep | Self-leveler as the finished floor |
| Broken into pieces, crumbling, or built with the wrong slope | Replacement | Lifting or an overlay |
| Open joints or a gap at the house | Flexible joint caulking | Mortar packed into the joint |
Glossary: Concrete Leveling Terms
Void: An empty or soft pocket under a slab where soil washed out, packed down, or rotted away. Rocking and hollow sounds come from voids. Lift: Raising a slab from underneath. Also the distance it rose, as in "a one-inch lift." Heave: Upward movement. Frost heave comes and goes with the seasons. Root heave keeps building. Offset: The height difference between two slabs, or between the two sides of a crack. Measure it at the low side. Overlay: Any new layer bonded or placed on top of existing concrete. Resurfacers are overlays. Underlayment: A layer made to be covered by flooring, not walked on as the finished surface. Polyjacking: Lifting a slab with polyurethane foam injected through small holes. Slabjacking: Lifting a slab by pumping material under it. Most often used to mean mudjacking. Pitch: The slope built into a slab so water drains off it.