How to Repair Concrete Cracks (DIY Guide)

Most concrete crack repairs are straightforward DIY projects. The key is matching the repair method to the crack size and type. Hairline cracks need simple sealers, wider cracks need flexible fillers, and structural cracks need professional assessment before any repair.

Done correctly, crack repairs prevent water infiltration, stop cracks from spreading, and extend your concrete's lifespan significantly. Done incorrectly—or with the wrong products—repairs fail within months.

Assess Before You Repair

Before grabbing a tube of filler, understand what you're dealing with:

Crack Width	Classification	DIY Repair?
<1/16"	Hairline	Yes
1/16" - 1/4"	Small	Yes
1/4" - 1/2"	Medium	Yes
>1/2"	Large	Maybe*
With displacement	Structural	No—get assessment

*Large cracks may indicate underlying problems. If causes aren't addressed, repairs will fail.

Also note:

• Is the crack stable (unchanged for months/years) or active (growing)?
• Is one side higher than the other (settlement)?
• Are there multiple parallel cracks (possible structural issue)?

For understanding crack causes, see why concrete cracks.

Repair Products by Crack Size

For Hairline Cracks (<1/16")

Best products:

• Concrete crack sealer (squeeze bottle applicator)
• Concrete caulk (for slightly larger hairline cracks)
• Waterproofing sealer (for general surface protection)

Why it works: These thin products wick into tiny cracks, sealing against water without requiring the crack to be widened.

For Small Cracks (1/16" - 1/4")

Best products:

• Polyurethane concrete caulk (Sikaflex, Quikrete Polyurethane)
• Elastomeric crack filler
• Self-leveling sealant (for horizontal surfaces)

Why it works: Flexible materials accommodate minor movement. Polyurethane won't crack again like rigid fillers.

For Medium Cracks (1/4" - 1/2")

Best products:

• Polyurethane caulk with foam backer rod
• Vinyl concrete patching compound
• Hydraulic cement (for wet conditions)

Why it works: Backer rod provides a base and limits filler depth. Patching compound creates a strong, durable repair.

For Large Cracks (>1/2")

Best products:

• Concrete mix for deep sections
• Epoxy injection (for structural repairs)
• Hydraulic cement (quick-setting, water-stopping)

Why it works: Larger cracks need material with structural strength. Fill from the bottom up in layers.

Step-by-Step Repair Process

Step 1: Clean the Crack

This is the most important step—repairs fail on dirty surfaces.

For all cracks:

1. Remove loose material with wire brush
2. Brush out debris (old dry brush works well)
3. Blow out dust with compressed air or shop vac
4. For greasy/oily cracks, use concrete degreaser
5. Rinse and let dry completely (24 hours minimum)

For wider cracks:

• Use chisel or screwdriver to remove crumbling edges
• Create slightly undercut edges (wider at bottom) for better adhesion
• Vacuum thoroughly

Step 2: Prepare the Crack

For cracks 1/4" or wider:

• Insert foam backer rod (slightly larger diameter than crack width)
• Push rod to about 1/2" below surface
• This limits filler depth and creates proper seal geometry

For deep cracks (>1"):

• Fill bottom portion with sand or pea gravel
• Leave top 1" for repair material
• For structural repairs, consult professional

Step 3: Apply the Filler

For caulk/sealant products:

1. Cut applicator tip at 45° angle
2. Apply steady pressure, filling from bottom up
3. Overfill slightly (materials shrink)
4. Tool smooth with plastic spoon or wet finger
5. Clean excess immediately

For patching compounds:

1. Mix per product directions (consistency matters)
2. Force material into crack with putty knife
3. Work from bottom up, eliminating air pockets
4. Overfill slightly
5. Smooth flush with surrounding surface
6. Feather edges for invisible repair

For concrete mix (large cracks):

1. Dampen crack edges (helps bonding)
2. Apply bonding adhesive if product directions require
3. Pack mix firmly, eliminating voids
4. Build up in layers if deeper than 1"
5. Finish to match surrounding texture

Step 4: Cure and Protect

• Follow product curing times before traffic
• Most caulks: 24-48 hours
• Patching compounds: 24-72 hours
• Concrete mix: 7 days minimum, 28 days for full strength

After curing:

• Consider sealing the entire slab to protect repair and prevent future cracks
• For more on this, see reinforcement options for new projects

Product Recommendations

Product Type	Brand Examples	Best For	Cost
Polyurethane caulk	Sikaflex, Quikrete Poly	Small-medium cracks	$8-12/tube
Self-leveling sealant	Quikrete Self-Leveling	Horizontal hairline-small	$7-10/tube
Vinyl patch	DAP Concrete Patch, Quikrete	Medium cracks, surface damage	$8-15/tub
Hydraulic cement	Quikrete Hydraulic, Drylok	Wet conditions, quick repairs	$10-15/tub
Epoxy injection	Simpson, Emecole	Structural cracks	$30-100/kit
Concrete resurfacer	Quikrete Resurfacer	Widespread surface damage	$25-35/bag

Common Repair Mistakes

Using the Wrong Product

Problem: Rigid fillers crack again in flexible applications; thin sealers don't fill wide cracks.

Solution: Match product to crack size (see tables above).

Skipping Surface Prep

Problem: Filler doesn't bond, pops out within weeks.

Solution: Clean thoroughly—wire brush, vacuum, degrease if needed. Let dry completely.

Filling Too Deep

Problem: Thick fills cure improperly, shrink excessively, or stay soft.

Solution: Use backer rod for depth control; fill large cracks in layers.

Repairing Structural Cracks

Problem: Cosmetic repair masks structural issues that continue worsening.

Solution: Get professional assessment for wide, growing, or displaced cracks before repair.

Ignoring the Cause

Problem: Repaired cracks reopen because underlying issue persists.

Solution: Address settlement (settling guide), drainage, or root problems first.

When NOT to DIY

Call a professional when:

• Cracks show displacement (one side higher)—indicates structural movement
• Foundation wall cracks are horizontal or stair-stepping—structural concern
• Cracks are multiplying rapidly—something is actively wrong
• Cracks exceed 1/2" and span large areas—may need mudjacking or replacement
• Repairs keep failing—underlying cause not addressed

Preventing Future Cracks

After repairing, minimize future cracking:

• Seal the slab every 2-5 years to prevent water intrusion
• Maintain drainage to prevent soil erosion beneath concrete
• Avoid deicing salts—use sand for traction instead
• Address settlement early before cracks worsen

Frequently Asked Questions

What is the best concrete crack filler?

For most residential cracks, polyurethane caulk (like Sikaflex or Quikrete Polyurethane Crack Sealant) is best. It's flexible, durable, and accommodates movement. For hairline cracks, self-leveling sealant works well. For large cracks, vinyl patching compound or concrete mix is better.

Can you repair structural concrete cracks yourself?

No—structural cracks (wide, growing, or with displacement) need professional assessment first. The crack may indicate foundation problems, soil failure, or structural deficiencies. Cosmetic repair of structural cracks masks problems and can be dangerous. Get an engineer's opinion before any repair.

How do you keep concrete crack repair from failing?

Three keys: (1) Clean the crack thoroughly—repairs fail on dirty surfaces, (2) Use the right product for the crack size—thin sealers for hairline, flexible caulk for small, patching compound for medium, and (3) Address the underlying cause—if settlement or drainage caused the crack, fix those issues first.

When should I replace instead of repair?

Consider replacement when repairs would cover more than 25-30% of the surface, when cracks indicate significant structural problems, when settlement exceeds what lifting can fix, or when the concrete is over 25 years old with multiple issues. At some point, replacement is more economical than repeated repairs.

Key Takeaways

• Match repair product to crack size—no single product works for all cracks
• Surface prep is critical—clean, dry, and free of loose material
• Polyurethane caulk is best for most small-medium residential cracks
• Use backer rod for cracks wider than 1/4"
• Don't DIY structural cracks—get professional assessment first
• Address causes before repairing symptoms

For project planning, use our concrete calculator if replacement makes more sense than repair. Visit our complete concrete guide for comprehensive project guidance.