An Overview of Asphalt Sealer Systems

Asphalt sealers are not slurry seals (Caltrans section 37.2 specifications) but a lot of people refer to asphalt sealers as slurry seals. Asphalt sealers have been in use for over 40 years and today there are basically three different sealer systems: Asphalt emulsion based sealers, clay emulsion based sealers and coal tar based sealers.

The first two systems are the ones most commonly used in California; coal tar systems are not heavily used except around asphalt paved areas sensitive to the dripping of oils and distillates such as airplane and truck fueling areas. They are still used extensively in the Eastern and SE United States but there have been health and environmental concerns regarding their use. These first two systems are plant blended compounds typically containing emulsified asphalt binder and selected mineral and fiber fillers (such as sand, slate, carbon black and cellulose fibers). They are intended to improve surface texture, protect the asphalt pavements from effects of weather erosion and oxidation, and provide a smooth, non-abrasive surface. Recommended for use on all asphalt parking lots and driveways, giving them a uniformly colored watertight seal. These sealers do not add thickness or structural quality to the asphalt.

What the property owner or property manager should look for:

Proper surface preparation: the asphalt should be as clean as possible—even power washed if needed. An asphalt sealer will fail if itis placed over a dirty surface. If there is a chance that there will still be some dusty areas when the sealer is applied, then you should consider requiring the area receive a tack coat applied first. Oil and grease spots should be cleaned (or even removed and replaced if bad enough), followed by the application of an oil spot sealer prior to the seal coat application. Otherwise, the oil will soak through the sealer. Cracks over _ inch but less than 1 inch should be cleaned and filled, using a cold or hot applied crack filler. Cracks over one inch should be filled with fine aggregate asphalt hot mix. Asphalt sealers are not designed to fill cracks—the sealer may seal cracks for a short time but will quickly reappear. The asphalt pavement should be dry although on very warm days or with very porous pavements, it is recommended that the pavement be pre-misted with water to keep the seal coat from drying out too quickly. As previously mentioned, asphalt sealing does not add any structural qualities to the asphalt pavement, so all failed asphalt should be removed and replaced with new asphalt hot mix.

The seal coat material should be diluted according to the manufacturers recommendations. It is important to add the correct amount of water—too much water will over dilute the sealer, causing it to lose its cementing or adhesion qualities, causing early failure. Not adding any water at all can cause the sealer to be too thick, causing shrinkage cracking and also leading to failure. The water and sealer should be fully mixed before application. Most manufacturers recommend two applications of sealer rather than one heavy coat. The amount of sealer used depends on the pavement surface.

Traffic should be kept off the sealcoat for as long as possible and practical—preferably at least 24 hours in warm weather but this is usually not possible on large parking lots so some scuffing from vehicles turning their tires may occur. Watering for irrigation around the sealed asphalt should be turned off for a minimum 24 hours also. 

If an asphalt pavement is properly designed and constructed, a maintenance plan of scheduled asphalt sealing will add many years of pavement service.