Effective cracksealing is one of the most important preventive maintenance measures for extending the life of asphalt pavement. When done correctly, cracksealing prevents water from infiltrating the pavement structure, protecting the base course and subgrade from saturation and eventual structural failure. This article covers the essential techniques and best practices for cracksealing that every pavement maintenance professional should know. For a broader perspective on equipment care, see our article on Construction Equipment Maintenance Programs a Complete Guide to preventive maintenance strategies.
Understanding Pavement Cracking: Types and Causes
Before any cracksealing program begins, it is essential to understand the types of cracks that develop in asphalt pavement. A proper pavement survey identifies these distresses early, allowing maintenance teams to address them before they worsen. The first distress that typically develops in new pavement is cracking, which generally appears in four distinct forms.
Longitudinal and Transverse Cracking
Longitudinal cracks run parallel to the pavement centerline, while transverse cracks run perpendicular. Both develop from several causes: paving joints separating, shrinkage of the pavement surface, and movement in the base or subgrade below. These are typically the first cracking distresses to appear and signal that the pavement is beginning to age and undergo stress from traffic and environmental conditions.
Block Thermal Cracking
Block cracking results from thermal changes and temperature fluctuations. As the pavement expands and contracts with temperature variations, combined with oxidation over time, the surface cracks in a pattern resembling squares or blocks. This type of cracking is especially common in regions with wide temperature swings between seasons and indicates that the pavement binder has lost much of its flexibility.
Crescent and Reflective Cracking
Crescent cracking forms along the edge of unconfined pavement surfaces such as streets, roads, and parking lots without curbs. This cracking occurs when the paved surface moves outward under traffic loading, creating crescent-shaped cracks at the pavement edge. Reflective cracking develops through new surface treatments such as chip seals, slurry seals, or overlays, emerging from existing cracks in the old pavement below. As the underlying pavement expands and contracts, the cracks reflect upward through the new surface. A stress-absorbing membrane fabric can slow the rate of reflective cracking, but some cracking will eventually show through. For more detail on pavement design and materials, refer to our article on Asphalt Pavement Engineering Mix Design Construction Methods Rehabilitation.
When and Why to Seal Cracks
Understanding the right timing for cracksealing is just as important as knowing how to do it. Once cracking begins, other structural distresses will develop if left unaddressed. The primary reason to seal cracks is to prevent water infiltration. All cracks provide a pathway for water to percolate through the paved surface, saturating the base course and subgrade below. When the base or subgrade becomes saturated, structural failures begin to develop rapidly.
The Quarter-Inch Threshold
Research studies conducted by several agencies have established that cracks with an opening of one-quarter inch or more penetrate all the way through a two-inch to three-inch paved surface. This finding makes the quarter-inch opening the standard threshold for cracksealing. Additionally, a minimum quarter-inch opening is required to achieve proper penetration of crack sealant into the crack. There are two key considerations when evaluating crack width:
- Cracks less than one-quarter inch wide often do not go all the way through the pavement surface and can be adequately filled by sealcoating
- Applying crackseal material to cracks narrower than the quarter-inch threshold wastes maintenance dollars because the material cannot penetrate properly and merely sits on the surface
As the pavement continues to oxidize and shrink over time, smaller cracks will develop into larger ones and new cracks will form. Regular inspection and timely intervention are essential components of an effective pavement maintenance strategy. For cost-effective planning of maintenance operations, review our guidance on Cost Control Strategies for Pavement Maintenance Contractors Lessons from international markets.
Edge Separation at Curbs and Gutters
Pavement adjacent to concrete curbs and valley gutters concrete swales will shrink and separate over time. These separations typically reach the quarter-inch threshold after five or more years from installation. Because curbs and gutters channel more water than the open pavement surface, these separation cracks are particularly vulnerable to water damage and must be sealed promptly when they reach the appropriate width.
Proper Crack Preparation and Material Selection
The success of any cracksealing operation depends heavily on two factors: proper crack preparation and selecting the right material for the job. Skipping either step will result in premature failure of the seal and wasted resources.
Crack Cleaning and Routing
Before any sealant is applied, the crack must be properly prepared to ensure adequate adhesion on both sides of the crack wall. The preparation process involves several steps:
- Inspect the crack to determine if routing is needed. Cracks narrower than one-quarter inch that are scheduled for cracksealing should be routed to open them to the minimum width
- Use compressed air to blow out all debris, sand, dirt, loose particles, and any noncompressible materials from the crack
- Ensure the crack is completely dry and free of moisture before applying any sealant
- Verify that the crack walls are clean and free of dust to promote proper bonding
Routing is an expensive task and may not always be practical for parking lots and homeowner association streets. However, some studies have found that creating reservoirs through routing can result in longer-lasting repairs, making the additional expense worthwhile for high-traffic areas or critical pavement sections.
Choosing the Right Crackseal Material
An elastomeric material, capable of expanding and contracting with the pavement as temperatures change, should be used as the crackseal material. The material must have a high enough softening point to eliminate tracking problems on sidewalks, pool areas, and interior carpets. Different geographical regions require materials with different softening points.
| Material Type | Application Method | Best For | Key Consideration |
|---|---|---|---|
| Hot-poured sealant | Pour pot or hose and wand under pressure | High-traffic areas, large projects, all crack types | Requires heating equipment on site; provides excellent penetration |
| Cold-poured sealant | Pour pot only | Small repairs, remote locations, light-duty pavements | No heating needed; gravity-fed application only |
| Low softening point material | Hot or cold applied | Cold climate regions | Risk of tracking in warm weather; use blotter material |
| High softening point material | Hot applied | Desert and hot climate regions | Resists softening in extreme heat; minimal tracking |
Several grades of cracksealant are designed for specific climate areas and conditions. When ambient and ground temperatures cause the crackseal material to soften and remain high consistently, it is recommended to apply a blotter material such as sand or Portland cement on the cracksealant as soon as it is applied. This blotter material prevents pickup by vehicles or pedestrians until the sealant has ample time to set up and cure.
Application Methods and Best Practices
Once the crack is properly prepared and the appropriate material selected, the application process must follow specific techniques to ensure a durable, long-lasting seal. The method chosen depends on the equipment available and the scale of the project.
Wand Application Under Pressure
Hot-poured sealant applied through a hose and wand under pressure is designed to penetrate deep into the crack. This method provides excellent results when done correctly. The critical requirement is that the tip of the wand must be placed at the entry of the crack to achieve proper application and maximum benefit. It is not acceptable for the material to be shot at the crack opening from a distance, as this prevents proper flow entry, creates a messy application, and increases material costs.
Pour Pot Application
Pour pot application relies on gravity to achieve material penetration, assisted by pressure applied by the operator. This is an acceptable method when the pour pot has the proper application foot that remains in contact with the surface, forcing material into the crack and banding it to both sides. The application foot serves dual purposes it directs material into the crack and spreads the band across the pavement surface.
Banding Technique
After the sealant is applied, it must be banded or spread on the pavement adjacent to the crack. The band should cover a width of one-third inch to one inch on both sides of the crack. A hand squeegee or a stationary foot on the pour pot creates the characteristic V-shaped band. This banding completes the cracksealing process and provides an additional seal against water entry. The key requirements for proper banding include:
- Apply the band immediately after filling the crack, while the material is still workable
- Ensure the band extends evenly on both sides of the crack
- Use consistent pressure to achieve uniform band width and thickness
- Avoid leaving puddles or thick spots that may remain tacky
Curing and Appearance Considerations
Cracksealant leaves a solid black band where it is installed, and this marking remains permanently in place. When applied before sealcoating, the cracksealant will be visible within hours after sealing. After the sealcoat wears off, the cracksealant will still be present and clearly visible. The material shadows through slurry seals and chip seals but is less visible than with sealcoats. There is little to no appearance of cracksealant through overlays, especially when a fabric interlayer is installed.
One important consideration is that cracksealant becomes soft and pliable when hot. Because of this elastic characteristic, striping sealant applied over cracksealant may flake off or disappear as the cracksealant moves with the expansion and contraction of the asphalt pavement. Maintenance crews should plan striping operations accordingly. Building a skilled and diverse workforce is essential for quality pavement maintenance. See our article on workforce development: Strategies for Building a Female Workforce in Construction and pavement maintenance.
Quality Control Checklist
To ensure every cracksealing operation meets professional standards, use the following quality control checklist:
- Verify crack width is at least one-quarter inch before sealing
- Confirm crack is clean, dry, and free of all debris and moisture
- Select the correct material grade for the local climate conditions
- Ensure application equipment is at the proper operating temperature for hot-poured materials
- Position wand tip at the crack entry point, not at a distance
- Apply sealant to fill the crack completely from bottom to surface
- Band the material one-third inch to one inch on both sides of the crack
- Apply blotter material if ambient temperatures are high enough to soften the sealant
- Allow adequate curing time before opening to traffic
- Document the date, material batch, and weather conditions for quality records
Regular cracksealing performed according to these best practices will significantly extend the service life of asphalt pavements, reduce the need for costly structural repairs, and protect the investment in paved surfaces. A well-executed cracksealing program is the foundation of any effective pavement preservation strategy.