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Asphalt Seal Coat: What It Does And Doesn't Do

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One person will tell you it's crucial to prevent complete disaster. Another will claim it's pointless and you shouldn't waste your time. The subject? Seal coating your driveway. But why is there such disagreement over how useful seal coating is?

Much of it stems from the fact that not everyone understands just what seal coating does and doesn't do. Once you know what to expect from asphalt sealant, you won't be expecting a magic elixir – and you'll know why it's still important for the health of asphalt pavement.

Doesn't: Penetrate And Renew Asphalt, Making It Like New

Sealcoat is just that: a sealant. It is designed to adhere to the surface of asphalt pavement and protect it, not soak into the asphalt and change it from within. In fact, if your asphalt is already cracked open and the interior exposed, those cracks need to be fixed before sealant can be applied.

Does: Protect Asphalt, Slowing Its Aging

The protective layer of sealant on asphalt slows the aging process. Technically, what is slowing down is the chemical oxidation of the asphalt binder. Exposed to air, the asphalt cures and hardens over time, becoming more brittle and prone to cracking. By protecting the asphalt from oxygen and the heat and light from the sun, a coat of sealant can slow down this hardening, prolonging the life of the pavement.

Doesn't: Completely Eliminate Cracking

Eventually, asphalt will need repairs. The more wear and tear it's subjected to, whether that's from heavy vehicles, high traffic, or temperature extremes, the more often these repairs will be necessary. Luckily, driveways aren't usually exposed to heavy vehicles or high traffic, so they hold up much longer than highways. However, they are still supporting cars and trucks and being exposed to various temperatures and weather conditions; they won't stay pristine forever.

Does: Prevent Cracking From Water Infiltration

What seal coating does is, again, slow down the rate at which asphalt needs repairs. Uncoated asphalt can be infiltrated by water, which soaks down between the aggregate of the pavement. The temperature drops, the water freezes and expands, and the asphalt is cracked apart from within. Sealed asphalt, on the other hand, lets water simply run off it and into the ground.

Doesn't: Let You Leave Gas And Oil Spills Indefinitely

Asphalt is a petroleum-based product itself, and it reacts to other petroleum products. This can cause problems if a vehicle leaks some oil or gas onto your driveway. Oil and gas seep down into asphalt, softening it and breaking it down. Let that spill sit long enough and, sealed or unsealed, your pavement will be in trouble.

Does: Protect Asphalt From Petroleum Products Long Enough For You To Clean Up

On an unsealed driveway, that oil and gas gets to work softening the asphalt right away. On a sealed driveway, the spill can't immediately soak down into the pavement; it sits on the surface. That gives you time to gather some rags, soak up the spill, and clean up your driveway.