In the asphalt sealcoating industry, there are two main types of asphalt sealer that can be applied to your asphalt. Coal tar and asphalt emulsion. You may think that the two products are exactly the same. They are black, they are used to seal asphalt, and they are applied by brush or spray application. While both products are used to solve the same problem, the two sealers are completely different.
Formulation
To begin with, Coal tar and asphalt emulsion sealers are two completely different formulas made with different raw materials. Coal tar sealer’s main ingredient is just that, coal tar. Coal tar is a thick, black liquid that is a byproduct of the distillation of bituminous coal (usually in the electricity production industry). Coal tar is mixed with additional minerals dependent upon the manufacturer. For decades, coal tar has been the king of sealcoating. The standard for all sealcoating professionals. However, within the past 20 years, a new type of asphalt sealcoat has become popular in the market, the asphalt emulsion. Asphalt emulsion’s main ingredient is asphalt cement, which is made from the same oils and materials that are used in the production of asphalt. The cement is then mixed with additional minerals, polymers, and emulsifiers to increase product durability and aggregate suspension. Using a sealcoat that is made from the same materials as your asphalt is a big advantage as the asphalt will absorb more of the vital oils that sealcoating replenishes.
Longevity
While both products are created to protect and beautify asphalt, there are clear differences in the performance between the two products. When asphalt emulsion sealcoat was first introduced decades ago, coal tar held the upper hand in longevity. Coal tar had been around for centuries at that point and was a reliable, well known product that manufacturers could create with their eye shut. However, within the past decade especially, manufacturers have significantly improved their chemical formulations for asphalt emulsions to the point where asphalt emulsion’s longevity consistently beats that of coal tar. The largest reason? Asphalt emulsion sealers contain a significantly higher solid content than coal tar (advantage of the asphalt base), which gives you more durability with the finished product.
Performance
The way the two sealers perform after application is another major difference. Once applied and cured (approximately 3 months after application) coal tar becomes an extremely hard coating that adheres to the top of the asphalt. This is what made coal tar the original king of sealers as this hard coating deterred oil and gasoline from being soaked into the asphalt. However, this hardened shell solution has one major drawback. Asphalt itself is a very flexible material. As the weather changes from fall to winter, and winter to spring, asphalt continuously expands and contracts. Unfortunately, the hardened coal tar on top of the asphalt does not expand and contract at the same rate as the asphalt, causing the coal tar sealant to crack. Continued use of coal tar sealer always results in spider web cracking of the sealer itself.
Since asphalt emulsion sealers are made using the same materials found in your asphalt, the sealcoat is absorbed into the asphalt and expands and contracts at the same rate as your asphalt, leaving you with no sealer cracking with continued use.
Continued use of coal tar sealer results in the sealer itself cracking. Notice how the sealer cracking spreads everywhere as coal tar sealer expands and contracts at a different rate than asphalt.
Health & Environmental Risk
Perhaps the largest difference between the two sealants are the risks associated with the two. In recent years, multiple studies have been conducted on the two sealants. The most shocking discovery has been the amount of cancerous polycyclic aromatic hydrocarbons (PAH’s) that are found within coal tar. As sealcoat wears on your driveway or parking lot, these PAH’s turn to dust and are carried away within the surrounding soil, making its way into streams, lakes, air ducts, and even your carpet. Don’t take our word for it. You can read more from the links below.
http://wemu.org/post/issues-environment-dangers-coal-tar-sealants
The risk associated with coal tar sealants is so great, that cities and even states all around America are beginning to ban the use of coal tar sealants including San Antonio Texas, Minnesota, and Washington (read more here http://www.eesi.org/articles/view/health-concerns-over-common-driveway-sealant-continue-to-prompt-local-bans ). Unfortunately, Pennsylvania currently does not have restrictions on the use of coal tar sealants.
Asphalt Emulsion sealants have been approved as a safe alternative to coal tar sealer nation wide and are increasing in popularity every single day. American Pavement Sealcoating has been offering asphalt emulsion sealer in the central Pennsylvania region for over 8 years and are proud to do our part in keeping our environment and and community safe.
Another relatively unknown risk with coal tar sealer takes place during application. When the sealer is first applied, coal tar produces “sealer burn” to the people and crew applying the product. Sealer burn is a sunburn type rash caused by the chemical vapor of coal tar itself. Crew members must wear full body clothing and face masks to avoid sealer burn. Asphalt emulsion sealcoats don’t produce any type of skin burns or irritation during application.
Crack-Sealing Adherence
When crack-sealer is applied to seal large cracks within your asphalt, the sealcoat is applied overtop to further protect and help hide the crack. In our experience, asphalt emulsion sealer has a superior advantage of being able to adhere and remain on top of the crack-sealer. Coal tar will adhere for about a month, but will then wash away from the crack-sealer, leaving the crack-sealer unprotected and left to stick out like a sore thumb (see pictures below).
This sealcoating job using coal tar is one month old. As you can see, the sealcoating did not adhere to the crack-sealing.
Odor
Coal tar sealers are notorious for their long lasting, foul odor that is elevated on hot summer days. These odors can last for months, even years depending upon how much coal tar sealant was used. Asphalt emulsions do not produce any irritating odors once dry.
So Why do So Many Contractors Still Use Coal Tar?
Because coal tar is an extremely easy and forgiving product to use. Since coal tar does not have as high of a solid content as asphalt emulsion, coal tar does not clog tanks and spray systems nearly as much as asphalt emulsion does. The high solid content in asphalt emulsion causes the sealer to set-up fast if not cared for in these systems.
Additionally, all coal tar sealers must be mixed with water. Asphalt emulsions on the other hand cannot be mixed with water due to the composition. So how can a coal tar contractor charge so little for sealcoating? Because all they have to do to retain their margin is add more water, sacrificing product quality.
Over our ten plus years of existence, we have used both coal tar and asphalt emulsion products. Our first hand experience has solidified the fact that asphalt emulsion is the far superior product, and is why American Pavement Sealcoating chooses asphalt emulsion sealer as our product of choice. You can learn more about our specific asphalt emulsion, Polymer Modified Masterseal here.