Hot Temperatures: Sealcoating applications under hot temperatures can be equally problematic. Sealcoatings should not be applied under the summer sun (90°F ambient) without first cooling the surface. If applied to a hot pavement that is too hot the sealcoating film almost gets "baked" as soon as it hits the pavement, resulting in a film full of pinholes.
The sudden loss of water immobilizes binder particles in the sealer and prevents them from fusing into each other and forming a continuous film. Devoid of the proper fusion process, binder particles do not effectively envelop the clay and filler particles in the sealer film.
As a result, binder stays as discrete particles not hardened by clay and filler particles. The sealer film, under such cure condition, may not reach the hardness and continue to stay sticky and soft. And that could lead to lead to a "tracking" problem, where the sealer may be tracked into the buildings and onto the carpet or tiles.
Mix design alteration suggestions:
Cool the pavement with a fine mist of water ("fogging"). Avoid puddling, otherwise sealer may just slide right off during application.
Not as effective as fogging but an acceptable and generally used approach is to add more water in the mix (3% to 5%), to increase fluidity.
Relative Humidity: Relative humidity (often referred to simply as humidity) is another major factor that greatly influences the film formation and final cure of the sealer. Relative humidity is the ratio of the actual moisture content of the air, at a specified temperature, to its total capacity. For example, 50% relative humidity means that only half of the air's total capacity is used and it is capable of absorbing another 50% of moisture or vapor from surroundings.
Conversely, at 90% relative humidity the air has very little capacity left (only 10%) to absorb additional moisture, thus drastically slowing down the release of water (cure) from the sealcoating film. The sealer film will release only the amount of water that can be accommodated by the atmosphere.
The atmosphere and the surrounding environment can be thought of as a sheet of paper towel: When dry it will soak up the spill, but it will not soak up the spill if the towel is too wet.
At 100% relative humidity the sealer film may take several hours, if not days, to cure.
The slow cure is further aggravated by low temperatures. For example, the rate of water evaporation is nearly halved for a 10-degree drop in temperature, at a given relative humidity.
Mix design alteration suggestions:
Reduce the water in the mix design; use only as much as needed for a good workable consistency. Another option is to allow longer drying time in between coats; do not apply the next coat even if the previous coat "looks" firm.
Wind Velocity: Wind velocity or air movement, especially under highly humid conditions, helps sealer dry faster than without any air movement. A light breeze assists in the dissipation of water and volatiles from the immediate vicinity.
On the other hand, sealer may dry too fast for properly handling windrows, under breezy conditions at low humidity (20% to 25%).
Mix design alteration suggestion:
Consider adding a bit more water if the sealer is drying too fast for proper flow and leveling of the wet sealer.
It's important contractors follow the mix design guidelines as suggested by their sealer manufacturer then consult with the manufacturer for special situations where the mix designs are not workable. The sealer manufacturer can provide alternatives including material preparation and application to match pavement or weather conditions.
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