How to Fix Concrete Cracks (and When to Call a Pro)

Concrete cracks. All of it, eventually. The question is never whether a crack is there. The question is what kind of crack it is, what caused it, and whether you are looking at something you can address yourself in a Saturday afternoon or something that will keep getting worse until a contractor fixes what is actually wrong underneath.

Most homeowners default to one of two mistakes: either they ignore cracks until they become a real problem, or they buy a tube of crack filler and treat every crack the same way regardless of what it is telling them. Neither approach works well.

This guide covers every common concrete surface, driveways, patios, walkways, steps, garage floors, and foundations, and gives you a clear framework for reading each situation correctly before you spend a dollar on anything.

Step 1: Read the Crack Before You Do Anything

Five minutes of observation before touching anything saves you from wasting money on a repair that will not hold or, worse, masking a structural problem that continues underneath a patched surface.

Ask these four questions about any crack before deciding what to do:

• How wide is it? Run a credit card edge across the crack. If it catches noticeably, the crack is approaching or exceeding a quarter inch, which puts it in a different category than a hairline crack you can barely see.
• Are the two edges at the same height? Run your hand across the crack. If one side is higher than the other, the slab has moved vertically. That is a structural indicator, not a cosmetic one.
• Is it growing? Mark each end of the crack with a pencil line and check it in 30 days. A crack that is extending or widening is not stable. Filling an unstable crack is temporary by definition.
• What surface is it on? A crack in a foundation is a different conversation than a crack in a patio. The same width crack carries different implications depending on whether it is on a decorative surface, a structural element, or a load-bearing slab.

Concrete Crack Types: What Each One Means

Hairline Cracks

Narrow surface cracks, typically less than an eighth of an inch wide, that run along the surface without depth. These develop as concrete cures and as the slab goes through temperature cycles over time. They are extremely common on all concrete surfaces and in most cases cosmetic.

What they mean: Normal aging and minor shrinkage. Not a structural concern unless they are growing.

DIY or pro? DIY in most cases for cosmetic treatment. Leave them alone if they are stable and not affecting drainage or creating a trip hazard.

Medium Cracks

Between an eighth and a half inch wide, with some visible depth. These are past the cosmetic category but may still be repair candidates depending on location, cause, and whether they are stable.

What they mean: More significant movement or stress than hairline cracks. The cause matters more than the width at this size.

DIY or pro? Assess the cause and stability before deciding. See the surface-specific sections below.

Wide or Structural Cracks

Wider than a half inch, cracks where one edge is higher than the other, or cracks that run the full width of a slab panel. These indicate structural movement in the slab, the base beneath it, or both.

What they mean: The slab has moved. Surface repair does not fix the cause.

DIY or pro? Contractor territory in almost every case. Surface patching treats the symptom. What is underneath is the actual problem.

Map Cracking or Crazing

A network of interconnected small cracks spread across an area in a pattern resembling a spiderweb. This is called crazing and typically results from the surface drying too quickly during the original pour, overworking the surface while wet, or a weak top layer in the original mix.

What they mean: A surface layer issue from the original installation. In early stages, cosmetic. In advanced stages, the surface layer is progressively failing.

DIY or pro? Early stage is manageable with sealing. Advanced crazing that has progressed to significant surface loss needs professional assessment before deciding on resurfacing or replacement.

Surface-by-Surface Guide

Driveways

Driveways take the most abuse of any residential concrete surface. Vehicle loads, oil, weather cycles, and the repeated stress of cars entering and exiting the same path every day create conditions that push cracks toward structural faster than other surfaces.

DIY territory: Hairline cracks and stable narrow cracks where both edges are flush. Clean the crack thoroughly, let it dry completely, fill with a polyurethane concrete crack filler, tool flush, and seal the full surface. A repair on a dirty or damp crack fails faster than the original crack would have.

Call a contractor when:

• The crack is wider than a half inch
• One side of the crack is higher than the other
• The crack runs the full width of a driveway panel
• Multiple cracks have appeared across the surface
• Water pools near the crack rather than draining away
• The same area has been repaired before and the crack returned

For a full driveway-specific guide including step-by-step DIY repair instructions, see our detailed article on fixing concrete driveway cracks.

Patios

Patio concrete does not carry vehicle loads, which means it handles stress differently than a driveway. Cracks on patios are more often caused by base settlement, clay soil movement, or tree root pressure than by load-bearing failure.

DIY territory: Hairline and narrow stable cracks on patios that are not growing, not creating drainage problems, and not near a tree root zone. Repair process is the same as driveways: clean, dry, fill, seal.

Call a contractor when:

• A section of the patio has sunk or shifted relative to adjacent sections
• Cracks run near a tree and one side is lifting
• Multiple cracks have spread across more than 20 percent of the patio surface
• The crack has created a drainage problem where water now pools on the surface
• The patio is more than 20 years old and showing widespread surface deterioration

Root-caused patio cracking deserves specific attention. In Stockton and the surrounding valley, mature trees with established root systems are one of the most common causes of patio cracking. A crack that follows a root path and has a visible lift on one side is not a repair candidate in the conventional sense because the root continues to grow. A contractor needs to assess whether root management, a partial replacement with a root barrier, or full replacement is the right call.

Walkways and Sidewalks

Walkways see consistent foot traffic but no vehicle loads, making them one of the more forgiving concrete surfaces for crack assessment. That said, walkway cracks that create a height difference between two sections are a trip hazard and a liability issue that moves them from cosmetic to urgent regardless of the cause.

DIY territory: Hairline cracks and stable narrow cracks where both edges are flush and no trip hazard exists.

Call a contractor when:

• Any crack has created a lip or height difference between sections, even a small one
• Cracks have appeared in multiple locations along the walkway
• Sections have shifted horizontally as well as vertically
• The walkway was poured thin, common in older properties, and cracks are spreading

A height difference of even a quarter inch at a crack edge is enough to catch a foot. If there is any vertical offset at a walkway crack, address it promptly. This is not an area where waiting to see if it gets worse is the right call.

Concrete Steps

Steps concentrate foot traffic and weather exposure on a relatively small area of concrete. They also dry and wet cycle differently than flat slabs because water runs across them rather than pooling. This means surface deterioration can happen faster on steps than on adjacent flat surfaces.

Common step crack patterns:

• Edge and corner spalling: the outer edges and corners of steps chip and break away over time. This is the most common step deterioration pattern and is typically cosmetic in early stages.
• Horizontal cracks running across the face of a step riser: these indicate the step is separating and are more serious than edge spalling.
• Cracks running down the length of a step tread: these often follow the pour joint between the step and the riser below it and indicate movement between sections.

DIY territory: Minor edge and corner spalling where the damage is surface-level and the step structure is intact. Hydraulic cement or a step repair mix can patch small areas. Surface prep is critical: the damaged area must be clean, dry, and free of loose material before any repair product bonds correctly.

Call a contractor when:

• Multiple steps are showing simultaneous deterioration
• Horizontal cracks appear on step risers
• Steps are separating from the house foundation or from adjacent retaining walls
• The step structure itself feels unstable underfoot
• Repair material has been applied before and has already failed or popped off

Repair material that pops off a step shortly after application almost always indicates inadequate surface preparation, a bonding agent that was not used, or repair material applied too thin. If a previous DIY repair failed, a contractor can assess whether the surface is suitable for another repair attempt or whether the steps need to be rebuilt.

Garage Floors

Garage floors are often the most neglected concrete surface in a residential property and one of the most revealing about the overall condition of a slab and its base. Because garage floors are enclosed and visible under artificial light, cracks that would blend into an outdoor surface in sunlight are often clearly visible inside.

What causes most garage floor cracks:

• Shrinkage during the original cure is the most common and most benign cause
• Settlement of the base beneath the slab over time
• Water infiltration through the foundation perimeter that erodes the base underneath
• Heavy equipment or vehicle loads on a slab that was not poured thick enough for that use

DIY territory: Hairline and narrow stable shrinkage cracks that have not changed in size. Clean, fill with an epoxy or polyurethane floor crack filler, and seal the full floor. Epoxy coatings applied over an unrepaired and unsealed garage floor will eventually fail at crack locations regardless of how well they are applied.

Call a contractor when:

• Cracks run from the perimeter of the garage toward the center, which suggests differential settlement
• Any section of the floor has sunk or heaved relative to adjacent sections
• Cracks appear near the garage door threshold or at the transition to the driveway apron, where vehicle loading is concentrated
• Water is entering the garage through cracks in the floor during or after rain, which indicates a drainage or grading issue outside

A garage floor with widespread cracking on a property with clay-heavy soil, common throughout Stockton and San Joaquin County, deserves a professional assessment before investing in surface repair or a coating system. If the base beneath the slab continues to move, any surface treatment will follow.

Foundations

Foundation cracks are categorically different from any other concrete surface covered in this article. A foundation crack is not a cosmetic issue and is not a DIY assessment. It is a structural question that requires professional evaluation before any other decision is made.

Types of foundation cracks and what they suggest:

• Vertical cracks: The most common foundation crack type. Often the result of concrete shrinkage during curing rather than structural movement. Stable, narrow vertical cracks that have not changed are generally less concerning than other crack types, but still warrant professional assessment rather than a homeowner judgment call.
• Horizontal cracks: The most serious foundation crack type. Horizontal cracking in a foundation wall indicates lateral soil pressure pushing against the wall. This is a structural failure mode that requires immediate professional evaluation. Do not attempt to patch horizontal foundation cracks and continue to wait.
• Diagonal cracks: Often indicate differential settlement, where one section of the foundation has moved more than adjacent sections. The angle and location of diagonal cracks relative to windows, doors, and corners helps a structural engineer assess the cause and severity.
• Stair-step cracks in block foundations: Indicate mortar joint failure between blocks. Common in older construction and can progress to block movement if not addressed.

The rule for foundations: Call a professional for any foundation crack assessment. This is not the surface where a homeowner should be making judgment calls about severity based on width alone. A structural engineer or experienced foundation contractor evaluates foundation cracks in the context of the whole structure, soil conditions, drainage, and the age of the building. That is a different skill set from assessing a patio crack.

DIY Repair: The Correct Process for Minor Cracks

For surfaces and crack types that fall into DIY territory based on the sections above, this is the correct process regardless of which surface you are working on.

What You Need

• Wire brush or crack chaser blade on an angle grinder
• Compressed air or leaf blower
• Concrete crack filler, polyurethane or epoxy depending on the application
• Backer rod foam for cracks deeper than a half inch
• Putty knife or caulk gun
• Concrete sealer appropriate for the surface

The Process

1. Clean the crack completely. This is the step most DIY repairs skip or rush, and it is why most DIY repairs fail prematurely. Scrub the inside of the crack with a wire brush to remove all loose material, dirt, and vegetation. Follow with compressed air to clear the dust. Any contamination left inside the crack prevents the filler from bonding.
2. Let it dry completely. Concrete crack fillers do not bond to wet surfaces. Wait at least 24 hours after any rain or washing before applying filler.
3. Install backer rod for deep cracks. If the crack is deeper than a half inch, push foam backer rod into the crack before applying filler. This gives the filler a surface to bond against without requiring you to fill the entire depth with product.
4. Apply the filler. Fill slightly above the surrounding surface to account for settling during cure. Do not overfill significantly. A slight overfill you can tool flush is better than an underfill that leaves a depression.
5. Tool flush. While the filler is still workable, use a putty knife to smooth it flush with the surrounding surface.
6. Cure completely before traffic. Follow the product's specified cure time. Rushing this step causes the repair to fail.
7. Seal the full surface. Once the repair has cured, seal the entire surface, not just the repaired area. Sealing protects the repair and produces a consistent appearance rather than a visible patch.

When to Stop and Call a Contractor

This is the most important section of this article and the clearest summary of the line between DIY and professional work.

Call a contractor when any of the following is true:

• The crack is wider than a half inch on any surface
• One side of the crack is higher than the other
• The crack is actively growing between seasons
• Multiple cracks have appeared across more than 20 percent of the surface
• Water pools near the crack or drainage has changed since the crack appeared
• The same area has been repaired before and the problem returned
• The surface is a foundation wall of any kind
• The crack is on steps that feel unstable underfoot
• You are not sure which category the crack falls into

A contractor assessing a structural crack evaluates the base beneath the slab, checks for vertical and horizontal movement, determines the likely cause, and recommends an approach that addresses the actual problem rather than the visible symptom. For significant cracks this may involve mudjacking, base regrading, partial or full replacement, or foundation repair depending on the surface and the cause.

Surface crack filler addresses the gap. What is underneath the gap is a different question that only a site assessment can answer.

Get a Free Concrete Assessment in Stockton

If you have a crack that falls outside the DIY category above, or if you are not sure which category it falls into, we can walk your property and give you a straight answer on what is actually happening and what makes sense to do about it.

Drago Inc. serves Stockton, Manteca, Tracy, Lodi, Lathrop, and surrounding communities throughout San Joaquin County. Licensed (CSLB #1017023) and insured since 2016.

Call us at (209) 871-8110 or request a free assessment online.

Frequently Asked Questions