What is Sealcoating?
Pavement maintenance contractors are not only the people who understand the importance of an aesthetically pleasing parking lot.

However, it is usually only the contractor who understands that the best way to maintain a parking lot is with a pavement maintenance plan. Pavement maintenance plans can vary in scope, but they never vary in purpose: to increase pavement life.

A pavement maintenance plan usually includes crack filling, pothole repair, and sealcoating, but it also can include sweeping. Sealcoating is one of the most important elements of a pavement maintenance plan because it slows pavement deterioration.

A sealcoat consists of either refined coal tar pitch (delivered from coke, a byproduct of the steel production process) or asphalt cement, (a byproduct of the petroleum-refining process) mixed with inert fillers, water, emulsifying agents, or additives. Applied in thin coats, this surface treatment is used to protect off-highway asphalt pavement surfaces such as parking lots, driveways, runways, service stations and heliports.

However, a sealcoat, like all pavement maintenance repairs, is a temporary means of inhibiting pavement deterioration and needs to be applied on a regular basis--about every two or three years.

Benefits of Sealcoating
If applied properly at the right time, sealcoating benefits the pavement in many ways:

Beautification. Fresh sealcoat brings a dark black color to the pavement, making it look and wear like new. A black parking lot has a clean, rich look that presents a positive image of the company, facility, or residential complex. Striping also enhances the beauty of a newly sealcoated parking lot.

Slows oxidation and water penetration. Exposure to oxygen hardens asphalt binders and results in a brittle pavement surface that soon cracks. These cracks permit water to penetrate into the subbase, weakening it and reducing pavement strength. This in turn leads to more cracks, which can eventually expand and become potholes. Sealcoats fill surface voids, reducing exposure to oxygen and prolong pavement life.

Resists gas and oil spills. Gasoline or oil leaking from an engine can soften asphalt. Because coal tars aren't soluable in gas or oil, coal tar sealers prevent this damage. And manufacturers of asphalt emulsion sealers usually add polymers to increase the resistance to gas or oil. By filling surface voids, sealing reduces the depth to which oil or gas can penetrate.

Easier to clean and maintain. Sealcoats fill surface voids while coating the pavement surface. The resulting smooth and even texture makes surfaces easier to maintain year-round--snow is easier to remove from a smooth surface, and sweeping is more effective on a smooth surface.

Increased pavement flexibility. A sealcoat keeps a parking lot black. The blacker it is, the more heat it draws from the sun; the more heat it draws, the more pliable it is, the more able it is to withstand traffic volume changes without cracking.

Protects asphalt from pressure washing. Sealcoat protects asphalt concrete from high-volume water pressure and detergents used in pressure washing dumpster areas and food-processing equipment.

Cost-effective in the long run. The price of asphalt concrete will always be affected by crude oil prices, which fluctuate when supplies vary. It's less expensive to sealcoat a parking lot every couple of years using a coal tar or asphalt emulsion than it is to overlay or place a new lot.

Surface Preparation. Proper sealing starts with good surface preparation. A new asphalt concrete overlay must be completely cured before any sealcoat can be applied. If applied too soon, (some manufacturers say less than 30 days is too soon) cool tar sealers might entrap asphalt volatiles at the asphalt/coal tar interface, softening the surface below the sealcoat. The sealcoat might take and peel off, or tracking might result.

Asphalt volatiles in a new overlay will also slow the curing of asphalt emulsion sealers if they're applied too soon. The sealer then might wear off prematurely. Old asphalt pavements might contain small (up to 3/8 in. wide) or large cracks and oil spots. Small cracks should be cleaned, large cracks filled with a crack sealant, and oil spots removed or treated with an oil spot primer to increase adhesion. Areas with numerous cracks or alligator cracking might need to be removed or replaced.

These surfaces might contain depressions, which will need to be brought up to grade with hot mix asphalt that's allowed to cure. Once these repairs are completed, all surface dirt and debris needs to be removed. This can be accomplished with a hand broom, power broom, or power blower. Dirt reduces the bond between the sealcoat and the pavement.

In addition, old pavement that's extremely dry (light gray in color) or that has exposed aggregate might need to be primed to improve sealcoat adhesion. The primer, a slow-setting emulsion (SSI-H) should be diluted with five parts clean water to one part emulsion and applied with brush or spray at a rate of approximately 1 gallon per 100 sq. ft.

If weather conditions don't allow for a complete settling of surface dust or if the air temperature is above 90 degrees fahrenheit, a contractor might need to treat the asphalt surface with a fine mist of water before applying the sealer. The mist should dampen the surface but leave no puddles or visible water. This improves adhesion by preventing the emulsion from breaking or curing too fast.

Mixing the material. Both coal tar and asphalt emulsion sealers need to be diluted with water before being applied. Average water-dilution ratios are about 20% to 30% (for every 100 gallons of sealer used, mix in 20 to 30 gallons of water). Some sealers also need to be mixed with mineral aggregate and a latex or polymer before application. A polymer is added to a coal tar and asphalt emulsion sealer to enhance its flexibility; resistance to oils, gasolines, and ultraviolet rays; and adhesion properties.
Always check the manufacturer's specs for recommended mix designs to bring about the best result.

Application. Most parking lots require two coats of sealer; home driveways usually receive one coat. Three coats are recommended only for surfaces that experience continuous traffic, such as drive-through lanes at restaurants and banks. Application procedures remain the same. Both types of sealers have a per-gallon coverage rate (when diluted) of about 35-50 square feet, depending on texture of the pavement surface.

First coat. A contractor uses either a squeegee, brush, spray wand, or distributor truck to place material in continuous parallel strips over the entire pavement surface. To eliminate all ridges and air pockets, a worker then spreads the sealer uniformly across the whole surface, including hard-to-reach areas near parking curbs.

Every coat of sealer should be thin (0.1 to 0.15 gallon per square yard) so it dries quickly and evenly. A sealcoat is dry when it is not sticky to the touch (time allowance: about 3 hours).

Second coat. The surface of the first coat must be clean before a second coat can be applied. Loose dirt can be blown off or swept off; hardened dirt or mud should be scrubbed off with a little water and rotating brush. The second coat should be of the same consistency as the first coat and can be applied in a like manner (some contractors do prefer to squeegee-apply a first coat and spray a second coat). To enhance bonding between both coats, the second should be applied at right angles to the first.

After the second coat is applied, the area should be blocked off for at least 24 hours to ensure a thorough curing of both sealcoats.