How to Crack Seal Right, Step By Step
In part one of our three-part series, The Ultimate Paving Maintenance Guide, we cover how to crack seal right, step by step.
Cracks come in all shapes and sizes. Sealing them in a timely manner is one of the most effective ways to maintain the quality of your pavement.
One of the biggest mistakes is waiting too long to begin maintenance.
“By crack sealing your pavement when cracks first appear, you keep the water and non-compressible materials out of the cracks,” said Glenn Shapiro, general manager of GemSeal Pavement Products’ northeast region. “These non-compressible objects will not compress as the crack contracts in warm weather. The pavement actually expands, making the crack width smaller, cracking and breaking the asphalt along the edge of the joint. By keeping water out, this will eliminate sub-base erosion, reduce freeze-thaw damage and improve ride quality of the pavement to extend its service life.”
“The magnitude of thermal movement,” which causes cracking, “depends on a variety of factors, including but not limited to, the amount of temperature change and the spacing of the cracks,” said Brandi Julian, sales training manager at Crafco Inc. “Understanding that all cracks move is imperative when designing your crack treatment.”
Choosing the right material, equipment and application for the job is also essential, Shapiro said.
Select Your Sealant
Sealants should be selected based on pavement condition, climate, pavement movement, service life needed and sealant properties, according to Julian. Although project specs may consider the other factors, it’s important to pay attention to the type of sealant you use, with or without project specs to follow.
For example, cooler climates require more flexible sealants than hotter climates.
“Using a softer material in a hot climate could cause tracking of the sealant by vehicle or pedestrian traffic,” Shapiro said. “In hot climates, there is less movement of the pavement surface in general and, therefore, no need for a very flexible material. If you use a less flexible material in a cooler climate, where the pavement will be exposed to greater temperature swings and will have more thermal movement, then the sealant may crack prematurely. This defeats the purpose of why you’re repairing the cracks in the first place.”
Another major factor in determining which sealant to use is the job type. For example, you don’t need a roadway sealant in a parking lot or a pedestrian area. Shapiro recommends that contractors working in parking lots use a sealant designed for pedestrian foot traffic, turning vehicles and parked vehicles—usually a stiffer material that loses tackiness when cured. However, that type of sealant is less flexible than roadway solutions.
Shapiro also recommends using a more flexible sealant on pavements with less than 20 percent crack density, and a stiffer sealant on pavements with higher crack density.
“Crack density is measured by looking at a 10-foot-by-10-foot section of the road or parking lot that best represents the average condition of the entire pavement,” Shapiro said. “Then measure the linear feet of cracks within the 100-square-foot area. The number of linear feet divided by 100 is the crack density.”
He also stresses that alligatored pavement is not a candidate for crack sealing, as it indicates failure of the sub-base and requires repairs beyond crack sealing.
Prepare for the Job
Before starting the job, you’ll need to consider the weather you’ll be working with.
“During spring and fall, cracks are in an average position—not completely open and not completely closed,” Julian said.
That’s the best time to crack seal. Most sealant manufacturers and agencies require a pavement surface temperature of 40 degrees and rising. You should also avoid sealing if rain is expected.
Before heading to the job, you’ll also need to make sure all of your equipment is in working order, that shaping tools are clean, and that you have the right wand tips for the job.
Once you arrive on the job site, you must prepare your cracks. According to Julian, cleaning the crack and ensuring it is dry is one of the most important aspects of successful application and good material adhesion.
According to Shapiro, one of the first steps is to use a router or saw to widen and deepen existing cracks and create a clean, solid edge for sealant to adhere to. “This process should extend the life of the sealant by up to 50 percent.”
“If [sealant adheres to unclean and unsound asphalt,] and there’s movement, the unsound asphalt may be pulled off by the sealant, or secondary cracking may occur,” Julian said.
When deciding between routing and sawing, it’s important to determine the types of cracks you’re dealing with. Shapiro said routing can follow existing cracks in any direction, but sawing can only cut straight cracks.
When routing, produce a rout centered over the crack to provide a uniform bonding surface on both sides of the crack. “Routing on one side of the crack is more likely to result in loss of adhesion on the side that wasn’t cut,” Julian said. She also suggests routing at least 1/8 of an inch from each side of the crack, but that the reservoir should never be wider than 1.5 inches or less than 3/8 of an inch. You should also pay attention to excessive spalling, taking care to inspect the cutters or pins to determine if they need to be replaced and slowing down your routing operations.
Shapiro recommends routing on roads with less than 20 percent crack density. “When sealing cracks in pavement with greater than 20 percent crack density, simple cleaning and sealing of the cracks is recommended,” he said.
Next, you’ll need to ensure the surface is clean and dry. Shapiro recommends using a compressor with sufficient pressure and velocity that is also equipped with a water trap to remove particles that could prevent bonding in the cracks. Julian recommends air pressure no less than 90 PSI and to keep the nozzle no more than 2 inches from the pavement surface. She also recommends walking forward, not backward, for best results, and elevating and fanning the nozzle across the pavement on the last pass to remove debris from the crack area to avoid blowing contaminants back into the cracks.
Julian adds that you can also clean with a vacuum or wire brush. Vacuum systems can be used in areas that are sensitive to air quality and do not permit compressed air blowing operations. Wire brushing involves a rotating, narrow, round wire brush that helps remove debris and is often used along with compressed air.
“Power brushing can be very effective at removing adhered surface coatings that compressed air cannot remove,” Julian said, adding that brushes do wear quickly and require frequent changing.
It’s important to ensure debris from one crack doesn’t get blown into cracks that have already been cleaned, and to time your operation so cleaning happens just before sealing to avoid debris blowing back into cleaned cracks.
Moisture, like dirt, can also be a barrier to adhesion. According to FHWA, using a hot air lance on the cracks will help minimize moisture.
Julian recommends using a hot air lance when crack sealing in moist climates, at night, and at temperatures below the dew point. “Hot air lancing cleans cracks by removing debris and burning vegetation, and dries cracks by removing moisture and warming the pavement,” she said. “It’s also useful for increasing pavement temperatures during cooler conditions or winter crack sealing.”
As the cracks can become moist quickly after hot air lancing, it’s important that your sealing operation happens shortly afterwards. However, you must take extreme care not to burn the pavement. Although slight darkening of the pavement is normal, excessive darkening, smoking or dislodgement of aggregates are signs of overheating.
“Any pavement that is saturated with water shouldn’t be sealed, even with a hot air lance,” Shapiro added. “Any dampness, discoloration due to moisture, as well as frost or dew should be avoided during crack sealing.”
According to Julian, while some bubbling in the installed sealant material is common, excessive bubbling can be caused by moisture in the crack, indicating that it should be dried to a greater degree before you continue sealing.
Apply the Sealant
During the application process, it’s important to maintain your material at the temperature recommended by the manufacturer, usually between 380 and 410 degrees Fahrenheit.
According to Julian, under-heated sealant will affect adhesion, and over-heated sealant will degrade the properties of the sealant. If sealant is under-heated, sealing operations should stop until the sealant is able to reach proper application temperature recommended by the manufacturer. Some over-heated material will be thick and stringy, while others will thin, depending on the sealant formula. Over-heated sealant must be disposed of.
You should check the temperature periodically throughout the job to ensure proper temperatures and keep the melter partially full—Julian suggests at least ¾ full—to help maintain temperature uniformity. She recommends adding sealant blocks one at a time at the installation rate, rather than all at once. Crack sealing operations do not need to stop as you add blocks, as long as you maintain the required temperature.
Although many melters self-regulate temperatures, it’s important to manually check as there may be areas of temperature variation within the melter kettle. If using unheated hoses and the temperature of the material exiting the hose doesn’t meet specified installation temperatures, circulate the product through the hose and back into the melter until the product reaches the appropriate temperature in the hose.
When filling the crack, it’s important to fill from the bottom up to assure a complete seal.
There are a variety of finishing techniques used in crack sealing. Overbanding acts as a “band-aid” over the crack, while reservoirs can improve adhesion and sealant life. Some projects call for a flush match of sealant and pavement, and some require a combination of techniques.
According to Julian, generally speaking, the longest lasting and most cost effective option is a routed reservoir with a band-aid to allow the pavement to move with changes in the pavement and protect the crack from damage.
In general, Shapiro said, cracks should be filled no higher than 1/8 of an inch above the pavement. “It’s necessary to keep the material tight to the pavement surface. This will keep it safe from tire imprint marks and snow plow damage,” he said.
To combat sagging as sealant cools and shrinks, some OEMs recommend filling the crack ¾ of the way and then allowing it to cool before filling completely. Other OEMs suggest filling the cracks to the proper height and returning to any cracks that are too low.
“You also want to keep drips and puddles to a minimum,” Julian said. Drips can be reduced by using a drip stopper on the tip. In the case of puddles of excess sealant, remove by heating a flat blade and cutting puddle excess without harming the treatment.
You should keep traffic off the crack sealed surface until the sealant has cured to avoid tracking. If you need to open the pavement to traffic quickly, blot the crack using either a detacking agent or limestone dust. Once blotted, the area can be opened to traffic immediately.
The Last Step is a Good Seal
Sealcoating is an important part of the pavement maintenance process. “Every year that goes by, the elements destroy some of the [asphalt cement] in the asphalt,” said Brent Loutzenhiser, owner of sealcoating tank manufacturer Seal-Rite.
Although he recommends that you always check with your sealcoat manufacturer for their recommendations, sealing new pavement within its first season could result in longer drying times for the sealant, but there comes a time when the customer needs to lock out the elements to protect his parking lot investment.
From then on, Loutzenhiser recommends sealing every 3 to 5 years, but it depends on the quality of the previous sealcoat, traffic, weather and other wear factors. For example, convenience store and fast food chain parking lots may need to be sealed annually.
When it comes to sealing well, Loutzenhiser sees some common mistakes. “The biggest mistake I see is when contractors don’t know how to mix the sealer, how to apply it, or even what kind of sealer it is,” he said. “So many people buy sealer from a middleman, and that’s fine, but you need to know who makes the sealer so you can find out how it’s supposed to be applied.
“Manufacturers have engineers that have spent a lot of time figuring out how to mix the sealer and the best way to apply it to make it last the longest,” Loutzenhiser continued. And it changes for every sealant from every manufacturer. “You need to follow each manufacturers’ instructions to make sure you’re doing it correctly.”
One of his personal pet peeves is neglecting to add sand, which adds needed friction, to the sealant. “Usually this is because they’ve had a machine that couldn’t handle it, or they didn’t know they needed to,” Loutzenhiser said. “If you have to go to court because someone slipped and got hurt on a lot you sealed, the manufacturer of that sealant will submit exactly how the sealant should have been applied. If you didn’t put sand in there when they said you needed to, you could be held liable.”