How late in autumn and early in spring can one go?
By Jeff Winke
Pushing it… pushing the envelope. The phrase is commonly understood, but the origins have nothing to do with a paper container for letters. It comes from science geeks referring to the mathematical envelope or intersection of consecutive curves being pushed beyond their range.
Tom Wolfe’s book about the space program, The Right Stuff, made “pushing the outside of the envelope” a popular notion when referring to the challenges and success of flight testing. That envelope is the description of the upper and lower limits of the various factors that it is safe to fly at, that is, speed, engine power, maneuverability, wind speed, altitude, etc. By “pushing the envelope,” that is, testing those limits, test pilots were able to determine just how far it was safe to go.
For asphalt paving contractors the right stuff challenge is pushing the production envelope of the seasons. How late in the autumn can work be completed, and how soon in the spring can work start up. This is particularly true when working with pavement sealcoating and knowing which additives can help push the production envelope.
“Additives that are designed to cure faster are able to extend the sealcoating season in the spring and in the fall by molecularly adding heat at the film level, creating faster evaporation and a better pavement bond early on,” stated Rick Poole, president, Diamond Shield Fortifier, Alexander, Arkansas. “But these products have limitations in that sealcoat conditions still need to be reasonably favorable enough to even apply sealcoat. Examples might be ground saturation levels that are unacceptable, temps forecast to fall too low at night before the coating can be dry enough, or really high humidity problems.” Cooler temperatures make it difficult for sealcoating.
“For the sealcoating to perform, it needs to be cured and form a complete film,” stated Nihal Pandrapragada, research chemist, STAR, Inc., Columbus, Ohio. “The curing happens with the coalescence of binder and polymer particles in the coating and release of water from the film. The issue with the cooler temperatures is that the binder particles stay hard enough not to coalesce; think of it as marbles hitting each other without fusing into each other.”
Pandrapragada continued, “The specialty additives designed for this purpose help to plasticize (to make those hard particles soft) to coalesce the binder and polymer components in the sealer and facilitate water evaporation at the same time, even at cooler temperatures, resulting in a complete film formation. The use of low temperature additives has enabled contractors to sealcoat even at cooler temperatures and extend the sealcoating season to early spring and late fall.”
Cautions regarding applying sealcoating in cooler weather have been around for awhile. It is old hat.
“Fast drying additives have been around for decades and have historically been used in the early spring and fall to speed up the dry times that are slowed by the cooler temperatures and overcast skies,” said Woodrow Adams, operations manager, with STAR, Inc. “However, we have come to the conclusion that fast-drying additives may actually detract from your sealers performance in cooler temperatures, causing premature wear and poor color. Recently, manufacturers have started developing additives specifically designed for sealcoatings to optimally cure under cooler ambient and surface temperatures. These new additives may actually slow down the drying process to allow the sealer film to cure sufficiently.”
Adams added, “Most weather limitations listed on asphalt sealer data sheets state that you should not apply sealer below 50° F, but this new additive technology has pushed the envelope. When utilizing cold weather additives, you’re now able to apply sealer at 40° F or colder. Depending on your geographical location, you stand to gain an additional 2-3 weeks of sealcoating in both the spring and fall.”
For now, specialty low temperature additives designed for sealcoating cure at low temperatures still have limits.
“Temperature is the major limitation,” Pandrapragada said. “At no point during application, drying and final cure, should the temperature drop near or below freezing. And, as always, one must make sure that there is no rain in the forecast for at least 24 hours from the application time. Also, be careful of the mix design. Follow the manufacturer’s recommendations regarding dosage amounts. Too low amount of the additive would result in uncured sealcoating and too high amount would be a waste of money without adding any benefit.”
The three-ton hippo in the room question becomes How far away are we from seeing sealcoat additives that will enable sealcoating all year long?
“Right now, it is far-fetched to imagine an additive to enable water based sealcoatings to be applied year around,” Pandrapragada said. “All the bets are off when the coating is exposed to freezing conditions. The solution lies in finding a way to prevent the coating from freezing (to ensure film formation) and to heat up the pavement to remove excess moisture (to ensure adhesion of coating to the pavement). It may be doable with other types of sealcoatings, e.g. chemically cured systems, which may be sufficient to heat up the pavement to drive off the moisture.”
Yet, one can hope that innovation will come along.
Poole concluded with a positive spin: “One day, we hope to see additives that can make year-round sealcoating possible, but for now, we need to be content realizing that additives are able to give some pretty decent, reasonable stretch to both ends of the work season that would not be possible or advisable without them.”
Jeff Winke is a business and construction writer based in Milwaukee, Wisconsin. He can be reached through firstname.lastname@example.org