Sealing asphalt is important for a number of reasons. It protects pavement from being damaged by oxygen and UV light, which harden asphalt and cause it to fracture under stress. It also keeps water from infiltrating the pavement, where it can wear away at the pavement or even freeze and crack it from the inside.
But deciding to get your asphalt sealed is just the first step. Next, you have to decide what type of sealant you want on your asphalt. Less expensive seals wear out more quickly, but that may not matter on low-traffic surfaces. High-traffic surfaces will have their sealant compromised more quickly, but it's possible to get impressively heavy-duty seal coat if you're willing to pay for it. So what type of seal is right for you?
Low-Traffic Rough Pavement: Fog Seal
Fog seal is the least expensive type of seal as well as the fastest to wear down. It involves spraying diluted asphalt onto the pavement, which hardens into a protective layer. The rougher the asphalt surface, the better fog seal works, flowing into the uneven surface and adhering to it. Low-traffic roads and parking lots with rougher surfaces are good candidates for fog seal.
While driveway sealant doesn't need to be very heavy-duty, fog seal is not usually used for this. Driveways, where traction is not very important, are often made of smoother asphalt for a more attractive surface. Fog seal will reduce the traction even further, causing the asphalt to become quite slippery. For this reason, parking lots with smooth asphalt should also avoid fog seal.
Low- and Medium-Traffic Driving Surfaces: Chip Seal
Chip seal has better traction than fog seal and is often found on driving surfaces; parking lots and driveways can also be chip sealed, but the added traction is less important to them. Chip seal begins like fog seal, with the application of asphalt emulsion; however, to prevent the slipperiness that fog seal creates, a layer of aggregate is pressed down into the emulsion.
Parking Surfaces: Slurry Seal
While chip seal adds traction, the advantage of slurry seal is that it is easy to apply and cures to an attractive surface, smooth but without the slipperiness of fog seal. The asphalt emulsion used in slurry seal is mixed with aggregate, usually finer aggregate than is pressed into a chip seal. This makes it an excellent choice for parking lots and driveways.
High-Traffic Driving Surfaces: Cape Seal
Cape seal is actually a combination of a chip seal followed by a slurry seal. Because of this two-step process, it requires more equipment, time, and money than other types of seal. However, it holds up very well to heavy use. For this reason, it's not generally used on driveways or parking lots. Cape seal is very effective on roads that are subject to high traffic or heavy loads.
Contact a professional contractor for more info on what type of asphalt sealant is right for your project.