A sealcoat is a preventive maintenance surface treatment designed to preserve and extend the life of a street. Preventive maintenance is like brushing your teeth or changing the oil in your car. It extends the life of the asset by preventing premature deterioration. To watch a video of the seal coat process CLICK HERE.
The City of Austin has been using the sealcoat method for several decades to keep streets in good condition and prolong their lifetime. The process is extremely effective as well as inexpensive, creating a good efficiency for our tax dollars.
How is the sealcoat program funded?
The sealcoat program is part of the annual Street & Bridge Division budget. The budget process begins in February and is approved by City Council in September for the following fiscal year – October through September. The sealcoat program has been part of the City budget for the past 40 years. It is an on-going annual program with the long-term goal of maintaining at least 80 percent of Austin’s streets in fair or better condition.
What is the process of a sealcoat?
The process starts by spraying a thin layer of asphalt and water emulsion over the pavement. The spreading of a thin layer of small gravel then follows. Afterward, the surface is rolled with a six-ton rubber tire roller and the street is reopened to traffic. A vacuum street sweeper sweeps up excess gravel the following day. It takes about a month for the new surface to completely cure and lock firmly into place and the road is open to regular traffic during this phase.
How long does the sealcoat process take?
Typically, on most streets the work is done very quickly, taking about 30 minutes per block, per lane. Some driveways may be blocked during this 30-minute period. As noted, while the road is reopened to traffic, the first sweeping does not take place for 24 to 36 hours and drivers are encouraged to drive slowly. After sweeping, the surface is still tender for the remainder of the curing process. Tight turns, quick accelerations, or sudden stops and heavy braking may leave permanent marks in the surface in the first few months, especially, on very hot days.
How will I be notified if a sealcoat is applied to my street?
A door hanger card will notify residents four weeks prior to scheduled work, and then again three days before our work begins.
Approximately what time will the crews be on my street?
The crews work during daylight hours from 8:00 AM- 3:30 PM on weekdays and 7:00 AM- 5:00 PM on some weekends. The sealcoat treatment must be applied in warm, dry weather, so the work is usually between May and October as weather permits. The work may be deferred if rain is in the forecast. If so, that street is rescheduled for the next clear workday.
Remember to call the Street Resurfacing Hotline at 512-974-9788 for the locations that will be sealcoated the next day. You can also call 311 if there are questions or requests for other City services.
What type of material is in the sealcoat?
Sealcoat is made up of an asphaltic binder and a uniform-sized aggregate gravel on the surface. An asphaltic binder is a water-based emulsion that does not contain any “coal tar”. Coal tar has been implicated as a contaminant in storm water runoff, which is why it is not used in our process. The sealcoat material protects an aging asphalt surface and seals up most of the small cracks to keep water out of the pavement.
Why is there excess gravel left on my street?
There will be some loose gravel particles that break loose under hard braking or fast acceleration. Also, we do not move parked cars during the sweeping phase, so there may be some loose gravel left behind under the cars. There may be some spots where the sweepers miss gravel, particularly at intersections or corners. However, all of this typically amounts to less than a gallon of gravel per block, and it does tend to accumulate at low spots, on the outside of curves, and at intersection corners. Please call 974-8777 if you need Street & Bridge to come sweep up any excess gravel left on your street.
The street appeared to be in good shape. Why was the sealcoat needed?
Asphalt streets consist of a 1½ to 2 inch layer of an asphaltic concrete. This mixture contains limestone rock and asphalt to bind it together. As the asphalt binder in the mix ages, weathers, and oxidizes, it becomes brittle. This causes cracks to form and water to penetrate into the pavement. The asphalt also loses it ability to hold the rock in place and the surface can start to lose rock and wear down. The rock itself starts to polish off and the street can become slicker in wet weather. While the old surface appears smooth, it contains hairline cracks that if not treated would continue to widen and deepen, eventually forming potholes.
Why does my street need to be sealcoated?
At first, the roadway asphalt aging process is slow, but after 9 to 10 years the process accelerates as cracks widen and allow more water to enter at more locations. The street will begin to contain a series of potholes and patches. The sealcoat process is applied to streets before they become badly cracked to stop the oxidation and slow the cracking process. A sealcoat can substantially extend the life of a street as much as 15 years if applied on a stable street surface.
Why did you stop before the cul-de-sac on my street?
Tandem axle, double tire garbage trucks make sharp turns in cul-de-sacs and cut into a standard sealcoat, thereby peeling up large sections of the surface. This is especially true in hotter weather. Instead, we skip all cul-de-sacs, and come back later with a different process to treat those areas. This other process is called a slurry seal. A slurry seal is applied by a contractor using specialized equipment, and requires the cul-de-sac to be closed for a longer period. Slurry seals are more expensive and don’t appear to extend the life of a street as much as a sealcoat, but the process works better for heavy trucks making slow-speed turns at the end of a street. Because slurry seal work is performed by a contractor, and because we don’t want construction traffic to interfere with either process, the slurry seal is usually done six months to a year after a sealcoat. Residents will again receive door hanger notifications when this treatment is planned.
Why are there skipped areas where cars were parked?
We will tow one or two cars to a neighboring street to allow the original sealcoat to be done. However, if there are a lot of cars or towing is not available, we will skip the area where cars are parked. In those cases, we will be back with a hand crew to cover those spaces at a later date. The crew uses the same materials, so the patch will blend in perfectly with the rest of the street.
How can the asphalt binder be removed?
If the asphalt emulsion is tracked onto shoes, carpets, or cars, WD-40 will soften the asphalt and allow it to be wiped off (but spot test carpets for color stability). If the material becomes stuck on people or pets, baby oil will dilute the material.
If the material is tracked onto a concrete driveway or sidewalk, do not dilute it, as it will soak into the concrete. If a large area is involved, sand blasting can remove the asphalt, but excessive blasting could damage the concrete finish. For smaller areas, it may be better to let the material wear off with normal traffic.
Sticky spots the size of dinner plates have appeared in the new sealcoat. Why did this happen?
When leaving your driveway, power steering turns can squeeze the gravel particles and roll them over, thus exposing the sticky side. This results in the dinner plate sized areas. Drivers can help limit these areas by slowly turning and using less power on the turns. If traffic hits that area again, the rock is often broken loose and pulled up. This problem is generally limited to specific driveways and becomes less likely as the surface cures, settles, and ages a little. In most cases, the affected areas are limited and will eventually blend in with the rest of the surface. If bare patches occur, we can spot seal those areas by hand.
Is the asphaltic binder harmful to our environment?
No. The asphalt binder is a water-based emulsion that does not contain any "coal tar." Coal tar has been used in some private parking lot resurfacing and was implicated as a contaminant in storm water runoff. The asphalt emulsion Austin uses is a completely different material. Once the original emulsification water has evaporated, the asphalt is no longer water-soluble and does not wash away after it is applied. The gravel aggregate is clean, hard gravel that does not leach, crumble, or break down.
The sealcoat surface is too rough. My kids can’t roller blade and my dog can’t walk in the street. What can be done to smooth it out?
The surface will smooth out over the first four to six weeks as the material cures and the gravel particles interlock and embed into a tighter surface. While this process is slow, it is happening. The street will look completely different in six to eight weeks with a darker, tighter, smoother surface. It will never be as slick as the old surface, but it will provide good wet weather traction and preserve the remaining life of the street, sealing most of the cracks. Dogs, cats, and squirrels are usually back on the street within 10 days!