How do you fix damaged concrete, and when should you replace it?

First, name the damage

Most concrete problems fall into a handful of types. Each has a different cause and a different fix, so the first step is to name what you see.

What you see	Name	Usual cause	Structural?
Fine web of shallow surface cracks	Crazing	Surface shrinkage from finishing and curing	No[4]
Straight or random cracks, edges level	Shrinkage or control cracks	Concrete shrinking as it dries	Rarely[1]
One side of a crack lower than the other	Settlement crack	Soil support lost	Depends; check the base
Thin flakes peeling off, sometimes exposing stone	Scaling	Freeze-thaw, deicing salt, weak surface	No, but progressive[3]
Small cone-shaped pits with broken stone at the bottom	Popouts	Porous aggregate swelling when frozen	Usually no[5]
Larger chunks breaking off, often at edges or over steel	Spalling	Corrosion, curled edges, freeze-thaw	Depends on depth[6]
Powder that rubs off the surface	Dusting	Weak surface layer	No[10]
Whole slab dropped or tilted	Settlement	Washout, poor fill, shrinking clay	Flatwork: no; house slab: ask an engineer

For detail on each crack type, see concrete cracks: types and fixes. For surface damage, see spalling, pitting and freeze-thaw damage.

Cracks are normal; some are not

NRMCA's guidance is plain: all concrete tends to crack, and it is not possible to produce completely crack-free concrete^[1]. Joints are just planned cracks. They are cut or tooled so that shrinkage cracks form in a straight line where you want them^[2]. NRMCA says most random cracks that appear at an early age rarely affect the structural integrity or service life of concrete, even though they look bad^[1].

The cracks that deserve attention are the ones that:

• Offset, so one side is higher than the other.
• Keep growing in width or length over months.
• Run into a house wall or foundation, or appear along with cracks indoors.
• Let water reach the soil under a slab in a freezing climate.

If you need to judge a crack's width, use our crack assessment checklist. For house slabs, see the crack width guide, which explains why no standard makes 1/8 inch "structural."

Myth: wire mesh or rebar stops cracks

It does not. NRMCA states that wire mesh and reinforcement in slabs cannot prevent cracking. Placed at the right depth, reinforcement can reduce how wide cracks open^[1]. NRMCA's joint guidance repeats the point: mesh will not prevent cracking, it tends to keep cracks and joints from opening up^[2]. So a contractor who promises "no cracks because we use mesh" is overselling.

The repair options

Crack sealing (routing and sealing)

This is the standard fix for non-structural cracks in flat slabs. The crack is widened into a clean groove and filled with a flexible joint sealant. The American Concrete Institute (ACI) describes it as a common, relatively simple method for floors and pavements where structural repair is not needed^[7]. It keeps water and salt out. For cracks that still move, a bond breaker at the bottom of the groove lets the sealant stretch^[7].

ACI also warns that unless the cause of cracking is corrected, new cracks will probably form near the original crack^[7]. If the cause cannot be removed, ACI's options are to rout and seal the crack and treat it as a joint, or to add support^[7].

Epoxy injection

Epoxy injection glues a crack back together. ACI says cracks as narrow as 0.002 inch can be bonded this way^[7]. ACI describes its use in buildings, bridges and dams^[7]. On a driveway or patio it is rarely needed, and gluing a crack that is still moving tends to push the crack somewhere nearby^[7].

Patching

Popouts and small spalls can be chipped clean and filled with a repair mortar. NRMCA's method for popouts: remove the remaining aggregate piece, clean the hole, and fill it with dry-pack mortar, epoxy mortar or a similar product. Matching the color of old concrete is hard^[5].

Resurfacing

A thin bonded overlay can restore a sound slab with light or moderate scaling, crazing or many popouts^[3][5]. NRMCA notes that the repaired surface is only as strong as the base it is bonded to, and that the old surface must be cleaned down to sound concrete first^[3]. HomeGuide puts resurfacing at $3 to $7 per square foot, with decorative or stamped overlays at $6 to $20^[8]. It reports that resurfacing lasts 8 to 15 years and that large cracks in the old slab quickly come through a new overlay^[8].

Hardeners and coatings for dusting

For a dusty interior slab such as a garage floor, NRMCA suggests removing the weak top layer and applying a chemical floor hardener on dry concrete. Coatings or grinding are the next steps if dusting persists^[10].

Lifting

If the slab is sound but sank, the repair is leveling, not patching. See concrete leveling.

Replacement

Replace when the slab is broken into many pieces, crumbling through its depth, scaled so badly the aggregate stands out over large areas, or sitting on a base that has washed away. NRMCA notes that repairing slabs with excessive and progressing scaling may not be feasible^[3]. HomeGuide advises replacing surfaces with large cracks, crumbling, spalling or structural problems, and says that if a repair needs a new layer more than 2 inches thick, replacement is the better option^[8].

Repair or replace: a quick decision table

Condition	Best first step
Hairline cracks, slab level	Leave it, or seal for water and salt
Cracks with no offset, slab sound	Rout and seal[7]
Sank but in large sound pieces	Lift, then seal joints
Light to moderate scaling or crazing	Clean, then resurface[3]
Scattered popouts	Patch[5]
Spalls over rusting steel	Engineer or experienced repair contractor[6]
Shattered, crumbling, or base washed out	Replace

What repairs cost

National prices from cost guides, with local variation:

Repair	Range	Source
Crack repair and sealing (as an add-on)	$250 to $800+	HomeGuide, Nov 2025[9]
Resurfacing	$3 to $7 per sq ft	HomeGuide, Feb 2026[8]
Decorative or stamped overlay	$6 to $20 per sq ft	HomeGuide, Feb 2026[8]
Mudjacking	$4 to $9 per sq ft	HomeGuide, Nov 2025[9]
Slab replacement	$6 to $15 per sq ft	HomeGuide, Nov 2025[9]

Labor rates, access, minimum charges and permit rules vary by city, so treat these as a starting point and get written quotes. For lifting prices, see concrete leveling cost.

Fix the cause, not just the crack

Most flatwork damage traces back to the same few causes. NRMCA lists the main ones: missing or poorly placed joints, poor subgrade preparation, too much water added to the mix on site, improper finishing, fast drying, and poor curing^[1]. You cannot change how a slab was poured. You can change the water around it. Point downspouts away, seal the joint between the slab and the house, and avoid harsh deicers. NRMCA says never to use ammonium sulfate, ammonium nitrate or magnesium-based deicers on concrete^[3].

Spalling over rusted steel is a different story. Rust takes up two to four times the volume of the original steel, which breaks off the concrete cover^[6]. That points to a structural or durability problem and should be looked at by someone qualified before it is patched.

When to call a pro

• Cracks with one side higher than the other, or cracks that keep growing.
• Spalls with rusted steel showing.
• Scaling or popouts spreading across a driveway every winter.
• Any crack in concrete attached to the house that appears along with cracks or sticking doors inside: see signs of slab foundation problems.