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While some areas may allow for a slope of up to 20%, this is often the maximum slope for driveways, with a few exceptions of up to 25%. Other regions may have a maximum of 12%, 15%, or 18%, so check with your local building department to ensure you’re laying a driveway that is up to code for your location.

Decomposed granite and caliche can both harden into a solid surface using a plate compactor. However, due to decomposed granite’s fine particles, it’s not suitable for driveway surfaces. Some homeowners use pea gravel mixed with a gravel-binding resin to bind the loose stones and create a solid surface that won’t shift like loose gravel.

While blacktop is a type of asphalt, the terms should not be used interchangeably, as not all asphalt qualifies as blacktop. The primary differences are in their composition, production process, and ideal applications. Blacktop contains more stone than other types of asphalt and is heated to a higher temperature during production—300°F or more—while hot-mix asphalt is heated to between 275°F and 300°F. The ratio of bitumen (a tar-like crude oil) is a key differentiator, though sources vary: some state blacktop has less bitumen, making it less durable, while others claim it has a higher ratio. Due to these differences, asphalt is generally more durable and better for high-traffic areas like highways and streets, while blacktop is more suitable for playgrounds and residential driveways. For a driveway project, it is best to consult a professional to determine the most appropriate material.

Asphalt and tarmac are not the same thing. Traditional tarmac, short for tarmacadam, uses tar as a binder to hold crushed stone together. Asphalt uses bitumen—a byproduct of crude oil—to bind aggregate. Though tarmac was once a go-to for roads, asphalt has become the modern standard. And these days, most surfaces referred to as “tarmac” are actually asphalt. So, while the names may overlap, the key distinction lies in the binder—tar for tarmac and bitumen for asphalt.