The scenario
A contractor knocks on your door unannounced and offers to sealcoat your asphalt driveway on the spot. He tells you about the great deal you'll get but fails to mention that he’ll be using watered-down sealant or used motor oil.

How to spot the scam
Sealcoat is an emulsion of coal tar or asphalt, water, and a fine aggregate like silica sand. If the contractor at your door doesn’t have a tank that’s actively mixing the sealcoating material, send him on his way. Other tip-offs to a problem beyond the cold call include the fact that his truck has an out-of-state license plate and his claims that the job can be done only “today.”

How the job should be done
Sealcoating helps protect the underlying pavement from air, sunlight, salts, and petroleum products. It also prevents water from turning hairline cracks into bigger ones. The aggregate in the mix enhances traction, acts as a wear layer, and fills small cracks. Also, sealcoating gives the driveway a uniform black color.

But sealcoating is a messy and tedious job to do yourself. To get a top-notch professional job, make sure that all of the steps outlined below are written into your contract and that the bid includes a total cost. Expect to pay $100 to $200 for a 30x14-foot driveway that doesn’t need patching. Here are the steps involved:
• The sealcoat should be applied when it’s at least 50°F and there is no forecast of rain for 48 hours. (New asphalt should be sealed only after it has cured for at least 90 days.) The contractor should apply the sealant with a brush, squeegee, or sprayer.
• The contractor should edge grass alongside the driveway and protect plantings.
• He should repair cracks in the asphalt and use a wire brush and other tools to clear the pavement surface of all loose debris.
• He should clean and prime oil and gas stains.

Keep in mind that your municipality might have restrictions on the type of sealant you use or when you can apply it. For instance, the city of Austin, Texas, has banned coal-tar-based sealants for environmental reasons. So before you apply a sealant to your driveway, check with your municipal government to determine if there are any bans or restrictions.

Sealcoating lasts for two to eight years depending on use and climate. To find a licensed pro, contact the National Pavement Contractors Association or the Asphalt Sealcoat Manufacturers Association.