Why Should I Sealcoat?
Off-road pavements (such as driveways and parking lots) are under continuous attack from the weather and other destructive elements, eventually developing minor surface cracks. Aggregates start unraveling producing minor cracks which widen and deepen with time. The damage will continue if proper protective actions are not taken.
   
There are many reasons to sealcoat. Below is excerpted information from several authoritative sources.
From the National Pavement Contractor's Association:
Asphalt pavements are made up of stone (aggregate) fine stone or sand, and asphalt cement. The asphalt cement is what gives the pavement it's black appearance and is the "glue" that holds everything together. Often I jokingly answer this question by asking "why do you paint the wood on your house?" It's obvious of course; to preserve the wood and protect it from damage from the elements. The same is true of asphalt pavements.
Have you noticed that new asphalt is jet black but soon begins to fade and in a year or two has turned gray? That's oxidation. The effects of the sun and rain/snow oxidizing the asphalt cement in the pavement. Given enough time the pavement becomes brittle and has less resistance to the loads placed on it. This can lead to a multitude of problems. Asphalt is a petroleum product so any other petroleum derivatives that contact it will dissolve into the asphalt, weakening or dissolving the asphalt's "glue like" properties. These substances commonly include motor oil, transmission/power steering/ or brake fluids, gasoline, and perhaps household solvents like some cleaners. It's common to see asphalt damaged by concrete cleaning products used on a sidewalk but rinsed onto a driveway. And the other common products mentioned can come from anywhere; a leaking car, oiling the chain on the kid's bikes, spills while servicing the lawnmower, the list is endless.
A good quality sealcoating will protect the asphalt pavement from all these damaging factors while providing the curb appeal of a new-looking black appearance. It's often overlooked that sealcoating not only seals the harmful elements out but seals the beneficial properties of the asphalt cement in. Many years of research has proven that proper maintenance including sealcoating can double the life of an asphalt pavement.
From www.AskTheBuilder.com - Tim Carter, nationally syndicated columnist. DEAR TIM: I was reviewing a quote I received to have my asphalt drive sealed. But it dawned on me that the streets in my community never get sealed. Is sealing an asphalt driveway really necessary? If so, when should they be sealed? Ron P. Westchester, OH
DEAR RON: There are several reasons why you don't see highway maintenance departments using traditional sealers on roadways. The heavy volume of traffic on the average road would rapidly wear away a surface coating of asphalt sealer. Roadways are also built differently than the average residential driveway. The engineers and government officials responsible for the design and maintenance of public roads plan for re-paving. In other words, since they know they can't seal, they plan ahead knowing the road must be re-paved every so many years.
The asphalt cement is a component of your driveway and public roadways. It is the glue that holds together the gravel and sand particles that actually make the superb driving surface. But the asphalt is damaged by the sun's ultraviolet (UV) rays and oxygen in the air. The UV rays and the oxidation cause the asphalt to become brittle. Brittle asphalt can crack. Cracks allow water to enter the paved surface. This water can freeze in colder climates causing further damage. The traffic on roadways actually wears away the brittle asphalt and exposes fresh asphalt. Furthermore, oil drippings from cars and trucks that get spread over the road surface actually acts as a low-grade sealer. But typical residential driveways don't get the traffic that roadways receive. Furthermore, oil spots on driveways are taboo. The bigger issue for residential asphalt driveways is cracks. Cracks that allow water to penetrate into the gravel base are a far greater threat to the long-term health care of your driveway. Water that enters the gravel base can then soften the soil under an asphalt drive. If this happens, the weight of the cars going over this soft area can cause the paved surface to crack in even more places. Remember, asphalt paving is actually a flexible pavement. The strength of asphalt surfaces comes from strong soils and a strong base material under the finished surface. Keep in mind that asphalt sealers are simply coatings that penetrate slightly into the asphalt surface. For the most part, they lay on top of the pavement. If you seal too often, you simply are adding layers of asphalt that can peel off. Asphalt drives should be sealed when you can clearly see the color of the stones that are used to make the asphalt paving. Where I live we use limestone stones to make asphalt paving. Left alone to weather, an asphalt driveway obtains a uniform color of gray. There are asphalt drives in my neighborhood that have not been sealed in 15 years. Had they been sealed three times in that time period I can't say that the driveway would be in any better condition. Absolutely do not seal a brand-new driveway. Fresh asphalt contains light-weight oils that eventually evaporate into the atmosphere. These oils are responsible for the tender nature of fresh asphalt. As these oils evaporate, the asphalt gets harder and harder. Sealers prevent this evaporation. Seal a new asphalt driveway and it may permanently stay soft. When you purchase asphalt crack and driveway sealers, use pricing as a barometer. Usually higher priced products contain higher quality materials. Pay attention to any temperature limitations on the product labels. Be sure the products can cure properly.
From www.About.com (excerpt)
Why bother sealing asphalt driveways? As water permeates cracks in the material and settles down at the base, the strength of the base is compromised, resulting in the formation of potholes. Cracks filled with water are also an open invitation in the North to damage from freezing. Even in warm climates, grass can begin to grow up through cracks on the edges of the surface. Damage from ultraviolet rays and oil/gas spills are other good reasons for sealing asphalt driveways.
From the Asphalt Sealcoat Manufacturers Association:
Sealcoating seals the asphalt pavement, preventing the oxidation and erosion of the top layer of asphalt. On older pavements sealcoating replaces fine particles lost from the asphalt surface due to oxidation. Sealcoating seals the small cracks that can turn into large cracks and prevents water from seeping down to the base material. Sealcoating helps protects the asphalt from the sun as well as the harmful effects of chemical spills such as oil and gasoline.
Sealcoating provides an attractive black surface that is ideal for painting lines and other markers. Sealcoating leaves a smooth, clean surface ideal for sweeping, lowering cleaning costs. Sealcoating costs pennies a square foot compared to the dollars needed to repair or replace damaged asphalt.
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