A Primer on Asphalt Repair and Maintenance

When discussing asphalt repair and maintenance, it is important to differentiate between a seal coat, an overlay and a resurface. In general terms, a seal coat refers to a light coating designed to prolong the life of an asphalt surface, an overlay refers to the placement of a layer of asphalt over the existing asphalt, and a resurface refers to the removal of the existing asphalt, often including a recompaction and leveling of the substrate, and the placement of a new asphalt surface.

The costs for these activities generally run from $0.07 to $0.10 per square foot for a seal coat, $0.50 to $0.75 per square foot for an overlay, and $1.50 to $2.50 per square foot for a resurface. Cost can vary outside these ranges depending on site specific conditions. The appropriate action depends on the condition of the paved surface. A general discussion of seal coating, overlaying and resurfacing is provided below.

Seal coating is generally considered a routine maintenance activity and is used to protect an asphalt surface and extend its useful life. There are many different types of products used in the application of asphalt seal coatings. The three main types of asphalt seal coatings are coal-tar emulsions (water-based) , asphalt emulsions and solvent-based emulsions with mineral spirits. The most commonly used seal coatings are the coal-tar and asphalt emulsion types.

Coal-tar emulsions are the most commonly used seal coatings. The advantages of using coal-tar emulsions are better protection from petroleum products (i.e. leaking automobile fluids, etc.) and a generally higher durability. Asphalt emulsions are not used as much as coal-tar emulsions because they generally are not as durable and do not protect against petroleum products. However, asphalt emulsions are more user-friendly during application. Solvent-based emulsions are rarely used. Polymer additives are commonly added to the sealant for more strength and durability. Sand is often added to the sealant for a rougher finish and/or to make the surface slip-resistant.

Many factors can affect the expected life of seal coatings including, but not limited to, the quality of workmanship, weather and volume of traffic. According to the majority of contractors interviewed by Aaron &Wright, the expected life of properly-applied seal coatings is approximately 3 to 5 years.

An asphalt overlay is used when cracks and holes are beginning to form, but the substrate is still in good condition. An asphalt overlay generally consists of placing a fresh layer of asphalt over the existing asphalt. The new layer is generally less than 2 inches in thickness. Most contractors consider the expected life of an asphalt overlay to be less than 15 years, but can be extended with proper maintenance. New asphalt should generally be seal coated after it has had a chance to cure. The curing usually takes 6 to 7 weeks.

If an asphalt surface has been neglected and water infiltration through cracks and holes has begun to undermine the substrate, the asphalt should be resurfaced. A resurfacing generally includes removal of the old asphalt and a recompaction of the substrate. The cost for such work depends upon the geographic location, the amount of grading and substrate work required, and other site specific factors. To avoid the expenses involved with resurfacing, it is generally prudent to maintain an asphalt surface using seal coats, spot patches and overlays.

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