The Effects of Rain on Asphalt Seal-Coating

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Seal-coating your driveway protects the asphalt.

Seal-coating your asphalt pays off because it not only makes your property look better, but it protects the asphalt, which can be damaged by ultraviolet oxidation and moisture, including rain. Even though asphalt does have good waterproofing and adhesive characteristics, it is a complicated mix of numerous chemicals that are an open chain in structure. When there is an open chain, this allows for access to weather, water, salt and other factors that can disintegrate the asphalt.


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What Happens When Asphalt Isn't Seal-Coated

When the molecules in asphalt disintegrate, the pavement loses it waterproofing and binding abilities, which causes the color of the pavement to change from black then to brown and then to gray. When groundwater freezes underneath the asphalt, this can crack the asphalt. This is called cryoturbation, or frost churning. Repeated freezing of the soil causes ice wedges to form and erode material. The material then moves upward or downward, and this can cause upheaval in your asphalt. If you use a seal-coating this is prevented.


Coal Tar Not Affected By Rain

A type of seal-coating often used is made from refined coal tar. The coal tar does not allow the elements of the weather or chemicals to bother it or the asphalt because it serves as a barrier coat. Rain does not bother the seal-coating. However, the pavement surface needs to be dry when applying the seal-coating.

Good Reasons to Seal-Coat

The elements, such as rain, wind frost, snow and ice, all break down asphalt and cause oxidation, which dries out the asphalt. Antifreeze, salt, oil and fuel also take their toll on asphalt, causing the cohesive properties, or what holds the asphalt together, and the oils in the asphalt to break down. When it rains, this causes raveling between the asphalt. Raveling means that the contents of the asphalt have separated. Man-made elements and natural elements can result in cracks in the asphalt in a mere five year's time. If you haven't seal-coated the asphalt, the small cracks serve as miniature storm drains after a rain. The cracks get bigger and this makes it possible for rainwater to penetrate through and to the base of the pavement. Large potholes and cracks may also develop within 10 years or even less time. When a pothole develops, this is the result of a portion of the asphalt breaking away and leaving a hole.


It's Like Sunblock

When you seal-coat asphalt, it is like applying sunblock to your skin. It protects the asphalt from sun damage. Low temperature or thermal cracking of asphalt can occur. Seal-coating the asphalt increases its ability to tolerate weathering and raveling, plus deterioration related to oxidation. The objective is to make the asphalt strong and durable enough to tolerate low and high temperatures and to increase its resistance to factors such as rainwater.