Crack Seal

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Small direct fired melters hold between 5 and 30 gallons of sealant and are typically used on small scale parking lot or residential pavement projects. Some melters are mounted on wheels, which allows the unit to apply the sealant directly to the crack.  

The heating system uses a propane burner, and agitation of the sealant is achieved by a manually operated lever.  These units have a temperature gauge, and temperature control is performed by manually adjusting the burner. 

Only use sealants that are recommended by the manufacturer for use in direct fired melters. The melters are designed only for low viscosity sealants that have been verified by the manufacturer to melt and apply properly with small direct fired melters.  High viscosity products, such as those with fiber, high amounts of  recycled rubber, or products that are very sensitive to heating temperatures, should not be used. When using these melters, all sealant that is melted and heated should be used within two to four hours.  

When using these melters, it is very important to ensure that the sealant product is not overheated. This is done by monitoring and controlling temperature and by maintaining agitation. If any melted sealant remains prior to a work stoppage, it should be drained and disposed of.  Sealant should not be left in the melter, allowed to cool, and reheated later, since the product can be damaged and its effectiveness can be reduced. 

Most hot applied sealants are heated for installation using oil jacketed double boiler melters. Oil jacketed double boiler melters use a double walled tank, with the space between the walls filled with heat transfer oil. The heating system heats the oil, and the oil transfers heat uniformly to the inner tank surface containing the sealant.  Heating systems are generally thermostatically controlled. The use of oil jacketed double boiler melters permit close temperature control of the sealant. Oil jacketed double boiler melters generally have agitation systems, and most have pumping systems used to apply the sealant to the pavement. Most use a diesel or propane fueled engine that operates a hydraulic system for the pump and agitator. Agitation of the sealant provides a uniformly heated material. More detailed description of desired oil jacketed double boiler melter characteristics may be found in ASTM D 6690 Appendix X1.1. 

When selecting a melter, consideration should not only be given to operating and productivity characteristics, but also to parts availability, service, maintenance and reliability.

Design features and options for oil jacketed double boiler melters include capacity, tank configurations, pumping systems, application systems, agitation systems, heating systems, and air compressors.  Most melters are designed as towable trailer units with either single or dual axles.  Some of the smaller capacity models are available as skid mounts that are placed in a truck bed.  Available melter tank capacities range from 50 to 400 gallons.  Large melters in the 200 to 400 gallon range are typically used by contractors on large scale, high volume sealing projects including state highways, interstates, and airports. Large melters can heat and apply up to 10,000 pounds of sealant per day.  Small melters between 50 and 100 gallons are typically used for smaller scale projects such as residential streets and parking lots. The most widely used size range is from 100 to 200 gallon capacity.

Both horizontal and vertical style tank configurations are available from different manufacturers. Pumping systems are typically used to recirculate the sealant and pump it through a wand onto the pavement. Internal and external pumping systems are available that can either be heated or not heated. On some large models, dual pumps are used to supply two applicator wands for faster application. Some lower cost melters are available without pumps, where the heated material is gravity fed out of a valve into pour pots for manual application. Standard pumping systems utilize valves on the equipment that control flow of material through the hose and wand; limiting the operators ability to start and stop crack sealing.  On-demand systems have a trigger on the wand itself to provide the operator with control of the flow of sealant. 

Heating systems are generally either diesel or propane fired burners. Agitation systems for melters vary in design and effectiveness. Full sweep rotating designs generally produce the best agitation and product uniformity.  Agitation speed can be adjusted with the hydraulic system.  Application systems for applying sealant to the pavement consist of a hose and a valve controlled wand with a tip. Heated hose systems are available on some units. Some melters are also available with on board air compressor systems used to clean out the cracks. This is a popular option that eliminates the need for a separate vehicle to tow the air compressor. Powered conveyor systems that automatically feed sealant blocks from a truck into the melter are also available to reduce labor for the sealing operation.  Many other options are also available on melters, including tool boxes, engine covers, arrow boards, strobe lights, lights for night work, overnight heaters for keeping the heat transfer oil warm,  and a variety of hitch and electrical connection variations.  

Compressed air is the most common method used for cleaning cracks. Air compressors should be capable of providing air at a minimum of 90 psi (pounds per square inch). The air is directed to the crack using a wand system with an appropriate tip that will maintain the 90 psi minimum pressure. Compressors need to be in good working condition and not emitting moisture or oil into the crack. Moisture or oil contamination of the crack can prevent the sealant from adhering.  Moisture or oil presence in the compressed air can be checked by blowing the airstream onto a piece of standard, uncoated cardboard, and examining for darkening which indicates presence of moisture or oil. When moisture or oil is present, it is recommended to use a moisture and oil trap. 

Ensure that your compressor is maintained as recommended by your manufacturer’s instructions. Check oils, drain the air receiver when necessary, and replace oil and air filters at regular intervals. 

High pressure air compressors provide a direct high pressure air flow which is effective at cleaning debris out of cracks prior to sealing. Cleaning the crack or cut reservoir is critical to enhance adhesion of the sealant to the sides and bottom of the crack. Sometimes more than one pass is needed for effective cleaning, especially in wide cracks. 

Operators should ensure the air compressor being used has the capacity to maintain effective high pressure throughout the duration of the project. 


Rotary impact routers have been in use for approximately forty years and are the most commonly used reservoir cutting equipment today. These routers cut using multiple star shaped, free spinning cutter bits, positioned around the perimeter of a high speed rotating flywheel. 

Rotary impact routers have a high production rate and can follow meandering cracks well.  Reservoir cutting rates can reach 600 to 800 linear feet per hour.  Cut width is set by the cutting head selected and positioning of the cutter bits, which can be staggered to make wider cuts. 

Depth of cut is set by the operator using an actuator controlled height adjustment of the unit. 

Carbide tipped cutters bits are most recommended as they produce quality cuts. Rotary impact routers are the most widely used type of crack reservoir cutting equipment.   A variety of options are available including self-propelled and dust control models.   


Normal crack cleaning operations involve removing dust, dirt, and other debris from the crack, which is deposited on the adjacent pavement surface and can create airborne dust.  In some areas that are sensitive to air quality, blowing compressed air is not permitted. To address this, crack cleaning systems that incorporate a vacuum system have been developed.  These systems consist of a vacuum hose attached to a wand and vacuum chamber that moves along the crack surface to pick up debris.   Some systems are available that incorporate compressed air blowing also within the vacuum chamber to agitate and loosen debris so that it can be removed by the vacuum. The debris is deposited in a canister, which is emptied periodically.  When using a vacuum system, sweepers are generally not needed to remove excess debris from the pavement surface. Use of vacuum systems results in decreased dust generation and a cleaner work environment. 


Hoses are available from a variety of manufactures. The two most common hose types are standard, which is unheated, and heated. Hoses are manufactured to handle liquid asphalt products typically up to 500°F (260°C) at 500 psi working pressure. Heated hoses work to maintain sealant application temperature all the way from the equipment, through the hose, the wand, and onto the pavement decreasing cold spots or solidifying in the hose during periods of inactivity. Standard hoses are typically less expensive than heated hoses, however, operators must circulate sealant in the hose back into the equipment during any period of inactivity to maintain proper application temperature and to avoid sealant solidifying in the hose. 

Hoses also come in a variety of lengths, with standard hoses commonly having a longer length than heated hoses. The hose length and design on the equipment will determine the working radius from the center of the machine. Hoses should be inspected regularly for wear and proper function. Operators should work a comfortable distance from the equipment and avoid working in circles, which cause the hose to twist around itself, to prevent kinks, knots, and pinch points on the heated hose. For the best, long-term sealant performance, it is imperative that hot-applied sealant is installed at the recommended temperature. 

Some larger melters are equipped to handle two hoses per unit for projects that demand higher production rates. 

Wand assemblies attach to the hose in order to apply sealant to the pavement. Typically wands are operated by a trigger as shown in the photo, or a valve controlled by the operator. 

Applicator wand tips are attached to the end of the applicator wand to assist with delivery and installation of the sealant to the crack. Several different types are available. Straight, elongated, and flush tips are typically used for recessed or flush fills. 

Sealing tips of different diameters such as sealing shoes and swivel discs are available for differing widths of cracks. Swivel discs pivot, allowing the operator to more easily apply sealant in a uniform overband from a variety of angles.

Applicator discs and shoes have several designs from 3 to 6 inches in diameter are used to form surface overband.  Sealant containing fiber should always be applied with a sealant applicator disc. 

The tip used for a project will depend upon the application configuration which may be detailed in the specifications. Most tips will fit to both heated and standard hoses, but it is always best to check with the manufacturer to ensure compatibility of the wand tip with the hose and wand being used.

Squeegees are commonly used for crack sealing.  They smooth out and level the sealant on the surface of the crack and form an overband.  Squeegees also help push the sealant down into the crack which can help with contact and adhesion to the crack wall. Squeegees are usually U- shaped. Squeegees may be metal or have a replaceable rubber blade.  Some squeegees can have a shaped cutout to assist with forming the appropriate overband thickness, width, and taper. Only squeegees designed for crack sealing projects should be used. Squeegees for garage use, or window cleaning, for example, should not be used.

Hot air lances should be used to dry slightly moist pavement or heat pavement up to 40°F (4°C), which is generally the minimum pavement surface temperature for most applications. The majority of hot air lances provide compressed air and heat to dry the crack and prep the surface for proper adhesion. Some agencies require a heat lance regardless of the surface temperature. It is always a good idea to familiarize yourself with the project specifications. Hot air blasting consists of using a hot air lance to clean cracks with high velocity, high pressure, heated air. Compressed air and propane fuel are supplied to the lance.  The propane burns in a combustion chamber and increases the air velocity as it expands.  The flame does not typically exit the lance, just the high velocity heated air.  The heated air is directed to the pavement crack to remove debris and clean the crack.  The heated air also heats the crack surface, helps to dry the crack, and if sealant is applied while the surface is still warm, adhesion can be enhanced. Typical heat lances heat the air to above 1000°F (538°C) at over 1500 feet per second velocity.  Heat lances must be used carefully; improper use can easily overheat the pavement and cause excessive hardening of the asphalt at the crack which creates early crack surface failures and adhesion loss. Signs of overheating include extreme darkening of the pavement, smoke, and dislodgement of aggregate.