There's More to Paving Than Sidewalks

Answers To 3 Common Questions About Asphalt Tack Coats

Asphalt is prone to degrade and decay over time--a problem often solved by the addition of fresh layers of asphalt. Unfortunately, these so-called overlays will themselves be doomed to fail unless a tack coat is first applied. If you would like to learn more about the tack coat's role in the asphalt repair process, read on. This article will answer three of the most commonly asked questions.

What does tack coat do?

The purpose of the tack coat is to rejuvenate the surface of the asphalt that needs to be repaired. That's because the older an asphalt surface gets, the less actual asphalt there is in the top layers. Sunlight, traffic, and water all act to wear it away. What is left behind is mainly exposed aggregate--i.e. the crushed gravel added to asphalt to give it stability and strength.

Unfortunately, asphalt overlay simply can't bond strongly enough to such a worn out surface. As a result, the overlay will tend to degrade much more quickly, developing dangerous and unsightly patches of spalling or raveling asphalt. A tack coat rejuvenates the asphalt at the surface of the existing roadway, thus enabling it to form a stronger and longer lasting bond with the overlay.

What is tack coat made of?

Tack coat essentially consists of asphalt that has been diluted to a thin enough consistency that it can be effectively sprayed across the surface in question. The tack coat may be diluted using either one of two substances: either hydrocarbons or water. Tack coat created using hydrocarbons is known as cutback. While effective, cutback is less commonly used today, due to environmental concerns about the volatile hydrocarbons leaching into nearby water sources.

Water-based tack coats--often referred to as asphalt emulsions--are a more environmentally friendly option. After being applied to the surface in need of repair, the water is given time to evaporate out of the tack coat, thus leaving behind a thin film of asphalt.

When should tack coat be used?

The easiest answer here is that a tack coat should be employed to increase bonding anytime an overlay is to be applied. That said, the thicker the overlay to be placed, the less important the tack coat becomes. But even in cases of an overlay of greater than four inches, a tack coat will still add an extra measure of durability as time goes on. Think of the tack coat as the most inexpensive type of insurance you can get for your asphalt surface.

For more information, talk to a professional like Arrow Blacktop & Masonry Inc.