Comparative ways to seal an asphalt driveway
Q. When we bought our house, our home inspector reported that the asphalt driveway was cracked and worn. He said the pavement would last longer if we would have it sealed. After moving in, we got bids from three paving companies and were surprised at the wide range of prices and the selection of sealants. One contractor recommended oil based sealant. The low bidder said that slurry is just as good. What are the differences?
A. Asphalt driveways often become cracked and worn because homeowners are unaware that maintenance is needed. As asphalt driveway get older, cracks eventually develop, allowing penetration of rain water. When this happens, the moistened ground beneath the pavement becomes soft. As cars and trucks drive over the surface, further cracking occurs, shortening the useful life of the pavement. To prevent this kind of damage, sealant is needed.
Three types of sealant are commonly used to resurface asphalt driveways: oil base, coal tar and water-based slurry. The type most often applied by do-it-yourselfers is slurry, an asphalt and cement mixture that can be applied like paint, using a roller or broom. This method is relatively simple and inexpensive, but slurry is not the material of choice if you're seeking a long-lasting, high-quality seal.
Slurry is lower in oil content than the other sealants. It tends to dry out, crack and peel within one to two years of application. This means resealing is needed at more frequent intervals than with other types of asphalt sealer, and once slurry begins to peel, it provides poor adhesion for subsequent applications of sealant.
Coal tar sealant is probably the most effective product for preventing water penetration into asphalt pavement, but its position in the marketplace has been challenged because of environmental concerns. This is unfortunate because coal tar sealants are the most durable and long-lasting of asphalt sealants. These products are a mixture of coal tar, sand, clay, polymers and other additives that make them pliable and durable. They are also unaffected by gasoline and oil spills. In some states, coal tar sealant is no longer available and it has even been banned in California and New York.
This leaves oil-based sealer, which is preferred over slurry because it achieves better penetration and adhesion to old, rough asphalt surfaces and is a longer-lasting solution, usually lasting four to six years, depending upon weather conditions.
Resealing asphalt driveways the do-it-yourself way is better than doing nothing at all, but professional application of oil-based sealant is the preferred way to prolong the useful life of your driveway.
• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.
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