Learn
How to recognize fatigue cracking, the base and water problems behind it, how it differs from other asphalt cracks, and why the repair has to go below the surface.
Last Updated:
Short answerAlligator cracking is a web of connected cracks in asphalt that looks like reptile scales. It is fatigue: the pavement bends under traffic over a base that is too weak, too wet or too thin, until it cracks through. Because the cause is underneath, the repair removes the failed asphalt and rebuilds the base; crack filler and sealcoat won't hold.
Alligator cracking in asphalt is the pattern of small, interconnected pieces that looks like the skin on an alligator’s back, and it is one of the clearest signs that a pavement has failed below the surface. Unlike a single crack from age or temperature, it means the asphalt is breaking from repeated bending over support that can’t carry the load. Sundial Driveway Repair is a service company offering and managing asphalt driveway repair and parking lot repair across Phoenix and its suburbs, fulfilled by licensed and insured contractors, and this guide explains what causes the pattern and how it is repaired.
It starts as fine cracks running side by side in the wheel path or along an edge, then links up into a mesh of irregular pieces, typically a few inches across. In early stages the cracks are tight and the surface is still level. As it develops, the cracks widen, edges crumble, the area sinks slightly and pieces begin to rock or come loose. The last stage is a pothole, once the pieces lift out and water reaches the base directly.
It tends to show up in predictable places: where wheels run, where a heavy vehicle parks, near an edge with no support, at a low spot that holds water, or downstream of a downspout or sprinkler. Where it shows up is a clue to why.
Asphalt is flexible. Every time a car rolls over it, it bends very slightly and springs back. Over a strong, dry base, that bending is tiny and the pavement lasts. Over a weak base, each pass bends it more, and the repeated bending fatigues the asphalt until cracks form at the bottom of the layer and work up to the surface. By the time the pattern shows on top, the damage underneath is already through the pavement.
The base gets weak in a few ways:
Heat plays a supporting part. Phoenix’s long summer softens asphalt binder by day, and years of sun oxidize it, making it stiffer and more brittle, so aged pavement cracks under bending sooner than fresh pavement would. The guide to how heat affects driveways in Phoenix covers the binder in detail.
Local soils and storms supply both of the main ingredients. In USDA soil survey samples, the survey lists low strength as a limitation for local roads at 51.0% of sampled points in Gilbert and 56.4% in Peoria, and shrink-swell clay at moderate or higher levels shows up at 78.4% of points in Gilbert and 76.9% in Chandler. Soil maps describe an area, not a lot, but where a drive sits on weak or clay-rich ground, the base and pavement thickness matter more.
Water arrives in bursts. Sky Harbor averages only 7.22 inches of rain a year, but about 4.1 days a year bring half an inch or more, and the National Weather Service’s monsoon season runs June 15 to September 30 (NOAA). Storm water running along a drive edge, a downspout emptying onto the pavement, sprinklers that spray the surface every day, and flood irrigation in some yards all keep the base wetter than rainfall alone would. The guide to driveway sinking after heavy rain covers how storm water undermines a drive, and driveway drainage covers the fixes.
The pattern tells you whether the problem is in the surface or the structure. The cornerstone guide on why driveways crack and sink has a full table of crack types; for asphalt the distinctions that matter are these:
| Crack pattern | What it looks like | Usual cause | Repair direction |
|---|---|---|---|
| Alligator (fatigue) cracking | Small interlocking pieces, in wheel paths or at edges | Weak, wet or thin pavement structure | Remove and rebuild the area, base included |
| Block cracking | Large rectangles, a foot or more across, over the whole surface | Aging and shrinkage of the binder | Crack filling and sealcoat; overlay if the base is sound |
| Longitudinal or transverse cracks | Single straight cracks along or across the drive | Temperature movement, joints between paving passes, reflection from below | Clean and fill or seal |
| Edge cracking | Cracks and breaks near an unsupported edge | Lack of edge support, water at the edge | Rebuild the edge and correct drainage |
| Raveling | Loose stone and a rough surface, no cracks | Aged binder losing its grip on the stone | Sealcoat if early; overlay if advanced |
Block cracking and alligator cracking are easy to confuse from a distance. Block cracks are large and spread evenly across the surface regardless of traffic. Alligator cracks are small, follow the loads and water, and come with sinking and loose pieces as they progress.
The repair depends on how much of the pavement is affected.
Localized cracking is cut out and rebuilt. The repair area is marked to extend past the visible cracks into sound pavement, since the asphalt just outside the pattern is usually weakened too. It is saw-cut with straight edges, the failed asphalt is removed, and the base is dug out where it is soft or wet, replaced with new aggregate and compacted. The edges of the cut are tacked so the new asphalt bonds, and hot-mix is placed in lifts, each compacted before the next. The finished patch sits flush and is sealed at its edges. Whatever caused the base to fail, such as a downspout or a sprinkler line, is corrected at the same time, or the patch fails the same way.
Extensive cracking calls for structural rehabilitation. When the pattern covers large parts of a driveway or lot, patching becomes a patchwork of seams, each a new path for water. The better course is a full-depth rebuild, which on a home is driveway replacement and on a business is commercial driveway repair: removing the old asphalt, correcting the subgrade and base, improving the drainage, and paving new asphalt at a thickness suited to the loads. On a commercial lot, that may be done in phases to keep the business open. The resurfacing vs replacement guide explains why an overlay alone isn’t enough here: a new layer laid straight over fatigue cracking reflects the same cracks within a short time.
The driveway condition assessment helps sort local from widespread damage before a visit.
Three treatments get sold for it that don’t fix it. Crack filler can’t bridge a mesh of moving pieces, and the cracks around it keep opening. Sealcoat is a thin surface coat; it hides the pattern for a season, and the sealcoating guide explains why it is maintenance for sound asphalt only. An overlay laid without removing the failed areas carries the same cracks up through the new surface. Each of these is cheaper than a proper repair, which is why they get offered, and each leaves the base failure in place.
Sooner is cheaper. Fatigue cracking only gets worse: open cracks let water into the base, the base weakens further, and an area that could be patched grows into one that needs rebuilding. Act soon if pieces are loose or rocking, the area has started to sink, water stands on it after storms, or it sits where a vehicle parks. Early, tight cracking in a small area can be planned around the season; just don’t let it go through a monsoon open.
If you are weighing a patch against a rebuild, the asphalt vs concrete guide is worth reading before deciding what to rebuild with. To get the area looked at, call the number at the top of this page or send a few photos of the cracked area with something for scale.
No. Filler can slow water getting into the cracks for a short time, but the pavement keeps flexing over the weak base and new cracks open around the filled ones. The pieces also keep breaking loose, so the area turns into a pothole. Filler is the right tool for isolated cracks in sound asphalt, not for fatigue cracking, which needs the failed area removed and the base rebuilt.
Not necessarily. If the cracking is confined to one area, such as under a downspout outlet, along one edge or where a truck parks, that area can be saw-cut out, the base rebuilt and new asphalt compacted in. The rest of the drive stays. When the pattern covers large parts of the surface, the base has failed broadly, and a full rebuild is usually better value than many patches.
There are two likely reasons: the patch replaced the asphalt but not the support under it, or it was cut too tight. If the base was still soft or wet, the new asphalt flexes over it the same way. If the cut stopped at the edge of the visible cracks, the weakened pavement just outside them keeps failing. A lasting patch extends past the cracked area and rebuilds the base.
Tell us the surface, what changed and the nearest cross streets. Photos of the damage and the street edge make the estimate more useful.
Asphalt driveway repair in Phoenix for potholes, alligator cracking and crumbling edges: saw-cut, infrared and crack-fill methods and ranges.
What a sealcoat does to asphalt under Valley sun, the driveways it helps and the ones it can't, how to time it around heat and monsoon storms, and what to check before paying for it.
What resurfacing actually is on concrete and on asphalt, the condition it needs underneath, how it compares on price with a rebuild, and the height and drainage questions an overlay raises.
How a rigid slab and a flexible pavement each respond to Valley heat, storms and soils, what each needs to stay sound, how they are repaired, and the City rules that apply at the street.
How a driveway is built, what the Valley's heat, soils and storms do to each layer, how to read the cracks you can see, and when a repair can wait.
What a monsoon storm does to the layers under a driveway, how to tell a washed-out base from a slab that is only cracked, and which repairs hold once the water is dealt with.