Crack Sealing: The Complete Guide to Asphalt Crack Repair

Crack sealing is the process of filling asphalt cracks with hot rubberized sealant that bonds to the pavement walls and flexes through temperature changes. It is the single most cost-effective thing you can do to extend the life of an asphalt surface, because it stops water from reaching the base. Water is what turns a hairline crack into a pothole, and a pothole into a full pavement failure.

What is crack sealing?

Crack sealing involves cleaning out a crack in the asphalt, heating it if necessary, and filling it with a hot rubberized material that adheres to the sides of the crack and remains flexible after it cools. The sealant moves with the pavement as it expands and contracts through freeze-thaw cycles, summer heat, and winter cold. It is not the same as dumping cold asphalt patch into a hole, and it is not the same as sealcoating over the surface.

The goal is simple: create a waterproof barrier inside the crack so that rain, irrigation runoff, and snowmelt cannot penetrate the asphalt surface and saturate the stone base underneath. Once water reaches the base, the base softens, the asphalt above it loses support, and the pavement begins to break apart under traffic.

Why cracks matter

Every crack in your asphalt is a direct channel for water to reach the base layer. Here is what happens when that channel stays open:

• Water enters the crack. Rain, sprinkler runoff, or melting snow flows down through the crack and into the aggregate base and subgrade below.
• The base softens. Saturated stone and soil lose their load-bearing capacity. The asphalt above it is now resting on a weakened foundation.
• Traffic flexes the pavement. Every car or truck that passes over the crack pushes the asphalt down into the softened base, then back up. This pumping action widens the crack and breaks the bond between asphalt layers.
• Freeze-thaw makes it worse. In Middle Tennessee, water inside a crack expands when it freezes, forcing the crack wider. A crack that was an eighth of an inch in October can be a half inch by March.
• The crack becomes a pothole. Once the edges of the crack start breaking apart under traffic, you have a pothole, and the repair cost just multiplied by ten.

Crack sealing vs crack filling

These terms are often used interchangeably, but they describe two different materials and two different levels of performance:

• Crack filling uses a cold-pour liquid or a lower-grade asphalt emulsion. It fills the void but does not bond aggressively to the crack walls and tends to harden and pull away within a season. It is appropriate for very small surface checks or as a temporary stopgap.
• Crack sealing uses hot rubberized sealant (typically ASTM D6690 material) that is heated to 350 to 400 degrees, poured into a cleaned crack, and squeegeed flush. It bonds to the asphalt walls and stays flexible for years.

If you are maintaining a commercial property, you want hot-pour crack sealing. Cold-pour filler is a hardware-store product for homeowners who need a temporary fix, not a maintenance strategy.

Types of cracks and what they mean

Not every crack should be sealed. The type of crack tells you whether sealing will help or whether you have a structural problem that sealing will only hide temporarily.

• Longitudinal cracks run parallel to the direction of paving. They often form along the joint between paving lanes. These are good candidates for sealing.
• Transverse cracks run across the pavement perpendicular to the paving direction. They are usually caused by thermal contraction and are excellent candidates for sealing.
• Block cracking creates a pattern of rectangular blocks across the surface. It indicates the asphalt binder has aged and become brittle. Sealable, but also a sign that sealcoating is overdue.
• Edge cracking occurs along the edges of pavement where there is no curb or shoulder support. Sealable, but the underlying edge also needs to be stabilized.
• Reflective cracking occurs when cracks from an older pavement layer below propagate up through a resurfacing. Sealable, but they will likely return.
• Alligator (fatigue) cracking looks like the skin of a reptile, with interconnected cracks forming a pattern. This is NOT a crack-sealing problem. It means the base has failed and the pavement is fatiguing under load. Sealant will not help. This area needs full-depth repair. See our guide to alligator cracking.

How the process works

A proper crack sealing job follows a specific sequence. Skipping any step reduces the lifespan of the repair.

• 1. Routing (optional but recommended). A router cuts a shallow, uniform channel along the crack. This creates clean walls for the sealant to bond to and a reservoir that holds the material. Not every crack needs routing, but high-traffic areas benefit from it.
• 2. Cleaning. Compressed air blows out dirt, debris, and vegetation from the crack. If the crack walls are dirty, the sealant will not bond.
• 3. Heating. A hot air lance may be used to warm the crack walls and dry any residual moisture. Sealant applied to cold, wet walls will not bond properly.
• 4. Application. Hot rubberized sealant is poured or pumped into the crack at roughly 350 to 400 degrees. It fills the crack from the bottom up.
• 5. Squeegee. The sealant is squeegeed flush with the surface so it does not create a bump that traffic can catch on. A blotting layer of fine sand or toilet paper is sometimes applied so the sealant does not pick up on tires before it cools.

How much crack sealing costs

Crack sealing in Middle Tennessee typically runs $1.50 to $2.00 per linear foot. The price varies based on crack width, the amount of routing or cleaning required, total linear footage, and whether it is bundled with sealcoating or striping.

Most commercial lots have a few hundred to a few thousand linear feet of cracks. A typical strip-mall lot might run $500 to $2,000 in crack sealing before sealcoating. The investment pays for itself by preventing the potholes and base failures that cost ten times as much to repair.

How long crack sealing lasts

Properly applied hot-pour crack sealant typically lasts two to four years. It does not last forever. The sealant itself ages, and new cracks will form as the pavement continues to flex and age. The goal is not to seal every crack once and be done. The goal is to make crack sealing part of your regular maintenance cycle, done before every sealcoat application.

Sealant that is pulling away from the crack walls, crumbling, or showing gaps should be cleaned out and resealed. The cost of resealing is lower than the original application because routing is usually not needed a second time.

When to seal cracks

• Before sealcoating. Always. Sealcoating over open cracks traps water and does nothing to seal them. Cracks should be sealed first, allowed to cool, and then sealcoated over.
• In spring or fall. Moderate temperatures give the sealant the best conditions to bond. Extreme summer heat makes the asphalt too soft, and winter cold makes cracks tight and hard to clean.
• When cracks are a quarter inch or wider. Hairline cracks narrower than that are difficult to fill and generally not worth sealing individually. They will be filled by the sealcoat itself.

When crack sealing will not help

• Alligator cracking. The interconnected pattern means the base is failing under traffic load. The area needs full-depth saw-cut repair, not sealant.
• Wide, deep cracks with vegetation. If grass is growing through the crack and the edges are crumbling, the base is likely compromised. Sealing the crack will hold water in, not keep it out.
• Structural failures. If the pavement is rutting, settling, or heaving, the problem is below the surface. Crack sealing addresses surface water intrusion, not structural failure.

Common crack sealing mistakes

• Sealing dirty cracks. Sealant applied over dirt and debris will not bond. It will look right for a week and then pull out.
• Not heating the sealant enough. Hot-pour sealant must reach the manufacturer's recommended temperature. Applied too cool, it will not flow into the crack or bond to the walls.
• Overfilling. A big blob of sealant above the surface gets caught by tires and snowplows and pulls out. Sealant should be flush or slightly recessed.
• Ignoring the cause. If a crack keeps returning in the same spot, there is a reason, usually base movement or drainage. Sealing it again and again is not a fix.
• Sealing over alligator cracks. It will not hold and it wastes your money. If you see alligator cracking, you need repair, not sealant.

Choosing a crack sealing contractor

Ask a contractor these questions before hiring them:

• What material do you use? (Look for ASTM D6690 hot-pour rubberized sealant.)
• Do you clean and dry the crack before application?
• Do you route cracks, or just blow them out?
• Do you squeegee the sealant flush?
• Do you apply a blotting layer so tires do not track the sealant?
• What is your warranty or expected lifespan?

A contractor who shows up with a bucket of cold-pour filler and a putty knife is not providing maintenance. They are providing a temporary cosmetic fix that will fail within months.