Reading the surface
What is alligator cracking?
Alligator cracking is asphalt broken into a pattern of small connected squares, and it means the base underneath that area has already failed.
The numbers
- It looks like the skin on an alligator: connected blocks, usually a few inches across.
- It is a base failure showing through the surface, not a surface failure.
- It appears where the loads are: wheel paths, entrances, dumpster approaches, dock doors.
- Crack filling and sealcoating do not repair it. The area gets cut out full depth and rebuilt.
What causes the pattern
Asphalt bends slightly under every vehicle and springs back, because the compacted stone under it holds it up. When that stone gets wet or thin or was never compacted properly, the asphalt over it bends further than it can take. It cracks, then the pieces between the cracks flex on their own and crack again, and you end up with the block pattern.
So the squares are the symptom. The cause is under them, and it is almost always water that got into the base through a crack somebody did not fill.
How to tell it apart from ordinary cracking
Ordinary surface cracks run in lines, often with the direction of the drive or along a seam where two passes of paving met. They are a surface problem and they fill well.
Alligator cracking is connected in both directions and it is in a patch rather than a line. Stand on it. It will usually give slightly, and sometimes water will come up through the cracks, which tells you the base under it is wet.
What the repair involves
The failed area gets cut out through sound asphalt on all four sides, the wet or loose base under it comes out, new base goes in and gets compacted, and new asphalt goes over the top and gets sealed at the seams.
The reason it is done that way rather than filled is the edge. A patch that meets broken asphalt has nothing to bond to and fails at the joint the first winter.