Greater Adhesion, Cohesion, Viscosity and More

By Jeff Winke

Starting point: Sealcoating is a protective coating to asphalt pavement, which provides a layer of protection from water, oils, and U.V. damage. And quite simply, sealcoat additives are designed to enhance different properties within the sealer to improve its performance.

“In general, additives contain polymers which enhance different properties within the sealer to improve durability,” stated Paul Raymond, technical manager with GemSeal Pavement Products, Tampa, Fla. “Properties impacted include adhesion, cohesion, and viscosity.

“Adhesion is how well the sealer bonds to the pavement. The better the sealer bites into the pavement, the harder it is to come off. Cohesion is the internal strength of the sealcoat itself, or how well it holds itself together. The greater the internal strength of the sealcoat film, the greater resistance it has to being worn off from traffic, as well as preventing sand rollout. Viscosity is a term used to describe how thick the sealer appears to be. Greater viscosity can help increase sand loading and affect how well the sealer spreads out on the pavement.”

There are primarily three types of pavement sealers. They are commonly known as refined tar-based (coal tar based), asphalt-based, and petroleum-based. All three have their advantages but are typically chosen by the contractors’ preference unless otherwise specified.

“Additives get a bad rap for only speeding up cure time; which plain and simply isn’t the truth, since additives bring many benefits to pavement sealcoat,” stated Adam Wellman with Maintenance Inc., Wooster, Ohio. “All of our additives are specifically formulated to help suspend sand, help eliminate tracking, add strength and flexibility to the sealer film for a long lasting great looking job. Additionally, additives are designed to give sealers a deeper black slate finish, leaving the asphalt looking wonderful.

“Additives can and should be used to help work around weather or at night. If you’re trying to get a job done with a threat of mother nature washing you out or nighttime sealing to accommodate the customer who does not want to close up shop during the day, there are additives that can cure out faster with less sunshine.”

Clearly there are benefits to sealcoat additives. Additives do add to the performance of the pavement being protected.

Some additives act like a drying agent to accelerate the drying and cure time of the sealcoat. “Dry” is when the sealcoat doesn’t transfer to the touch, and “cure” is when all the moisture has been driven out of the sealcoat and it is fully set (adhesive and cohesive strength reaches its strongest point, and the film cannot be re-dissolved in water).

“There is a class of additives that are used to prevent stripping of asphalt from aggregates which are, naturally, called ‘anti-stripping agents,’ and are specific to the type of aggregates used,” stated Girish C Dubey, president of STAR, Inc., Columbus, Ohio. “They are other types of additives that I have come across in my research that include deodorizing agents to suppress the odor of asphalt and additives for low temperature paving, which are a major advancement that are worth noting.”

Additives come in many types and offer many solutions to asphalt pavement contractors.

“There are latex and polymar sealers,” explained Robb Archie, owner, U.S. Seal International, Inc., Reno, Nev. “Additives benefit sealcoats. It can change the viscosity, making the sealer thicker and better able to suspend the aggregate. Additives can improve adhesion to the asphalt pavement and reduce drying time while providing a richer color to the finish.”

Archie described a project which showcases the benefits of sealcoating. He explained that he has a very long driveway leading to his own home that was built and paved 35 years ago.

“Sealcoating has extended the life of my very long residential driveway considerably,” Archie said. “I apply sealcoating every two or three years at a cost of $12,000. If I were to repave the driveway, the cost would be $82,000. Not only does sealcoat maintenance cost less, the results are spectacular. The sealcoat finish looks rich and dark as though it had just been freshly paved.”

Wellman has a contractor who had a challenging job that required sealcoating.

“The contractor had quite a large sealcoating project for a number of gas stations that came with a substantial payday… and a stipulation,” said Wellman. “The owner of the stations gave him the job, but would only shut down his stations for four hours at night, which to any sealcoating contractor is a huge issue to put traffic on a freshly sealed lot that fast. My customer came to me for help.

“We literally went into our lab and created samples with varying percentages of our additives trying to figure out the best possible solution. We provided him with a mix we felt confident would work. We still held our breath, when our customer came in the next day. He was all smiles, because the mix we designed for him worked to a T and he was able to put two coats of sealer down on this lot and open it in the four-hour allotted time frame and had no tracking!”

In general, sealcoats can benefit from additives when the pavement surface is aged, exposed to chemicals (such as motor oil, road salt), receives heavy traffic, experiences weather extremes or moderate exposure to sun.

Jeff Winke is a business and construction writer based in Milwaukee, Wisconsin. He can be reached through