What is an Asphalt Seal Coat? Why is it Important?

A brand new, fresh asphalt parking lot or driveway is a beautiful thing. The crisp lines, smooth surface, and consistent black color make it very visually appealing. But what about old asphalt? Far too often we see asphalt that has not been well maintained and has quickly become weak, deteriorated, bumpy, and ugly. This outcome is not inevitable. Doing just a few simple things can keep your asphalt in good working order for decades.

First, let’s quickly discuss how asphalt surfaces are designed. Proper roadways are initially excavated down to remove any organic material in the soil. Soil that does not compact well is also removed gravel and road base is then brought in and thoroughly compacted. A good road base, when properly compacted, becomes very hard, almost rock solid. Asphalt is then applied over the top of the road base. As long as the asphalt is in good condition, it keeps the road base dry and in its proper place.

Asphalt may seem to be a permanent material, but it is very susceptible to water, sun, water, petroleum products, and salts. This deterioration process begins when asphalt pavement is exposed to sun, wind and water, and then the asphalt hardens, or oxidizes. This causes the pavement to become less flexible. This flexibility is extremely important because asphalt can take great loads and bounce back to its original condition.

As asphalt loses its flexibility it becomes brittle and begins to crack and break. As a result, water enters these cracks and seeps down into the road base under the asphalt. This causes the base material to move and settle leading to further cracking and an “alligator appearance.” When the asphalt reaches this stage, the only option is the removal and replacement of the asphalt. Application of a seal coat, simply a new layer of material containing tar, sand, and other fillers, over your surface every 2-5 years will help protect the asphalt.

This type of seal coat protects the asphalt from harmful UV rays, and allows it to remain flexible. On older parking surfaces, a seal coat replaces the fine sand particulates in the top of the asphalt. It also seals the small cracks in the surface, stopping them before they become large cracks. This then acts as a water barrier and all the water then drains off the asphalt, instead of soaking through the asphalt, and softening the road base. Seal coats also leave a smooth, black surface, that is easy to sweep and maintain.

Another reason for a seal coat is to increase traction. When asphalt ages, the fine particles wear away. This could lead to surfaces that do not have any traction. A seal coat increases the aggregate on the surface and also the traction.