Q I’m going to seal my asphalt driveway. I’ve never done this before, and I don’t want to make a mess out of it. I would appreciate any advice you can give me about what kind of sealer to use and the best way to do this work.

A Sealing a driveway is about as simple as DIY projects go, and freshly sealed asphalt can make a world of difference to a home’s attractiveness, not to mention greatly increase the pavement’s durability.

Begin by cleaning the driveway with a stiff-bristle broom or a leaf blower. Scrape clean any cracks that are filled with weeds (use an old reciprocating-saw blade for this). Patch and firmly compact potholes with cold-patch asphalt, and seal cracks with crack filler. To repair large cracks, either pack the bottom with sand or lay in a length of foam backer rod before applying crack sealer. Next, apply oil-spot primer to greasy spots with an old paintbrush. This prevents the spot from bleeding through the seal coat.

Finally, use masking tape, paper and sheet plastic to protect adjoining surfaces, such as sidewalks, foundation walls, garage doors or floors, or retaining walls. Sealer that gets splashed accidentally on these surfaces is nearly impossible to remove.

You’ve got several choices of driveway sealer. Coal-tar sealant is the traditional product; its primary component is the refined tar formed when bituminous coal is converted to coke, a steel-making fuel. Coal-tar sealer is still the go-to material of the road-sealant industry; it’s favoured because it resists degradation from the Sun’s UV rays and doesn’t dissolve easily when blemished by motor oil and automotive chemicals.

Coal tar, however, is at the centre of an ongoing controversy. In 2006, Austin, Texas, banned asphalt sealers that contain the material, citing a study that found polycyclic aromatic hydrocarbons (PAHs) had accumulated in waterways. An industry trade group, the Pavement Coatings Technology Council, fi red back with counterstudies that took that research to task for flawed methodology, and noted that PAHs are also found in automotive exhaust and the residue from burning wood and charcoal, among other sources.

Where does that leave you? Coal-tar sealants are still readily available, but if the possible environmental risk concerns you, then your best choice is to use a sealer formulated from asphalt emulsions (which contain a tiny fraction of the PAHs found in coal-tar formulations). There are also sealers made from acrylic emulsions. Although I haven’t seen data on PAHs in acrylics, I would estimate that their level is at least as low as in asphalt emulsions and probably lower. Expect to pay three to four times the price of asphalt-emulsion blends if you go the acrylic sealer route.

Regardless of the sealer you use, reduce chemical-containing runoff from the driveway by applying the sealer when the forecast
is for dry weather. The longer the post-application stretch of dry weather, the better. The sealer should have a chance to cure
before it rains.