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Sealcoating professionals often ask how to adjust mix design for weather-related conditions, for sand/aggregate loadings, or simply for the amount of water in the mix.

Contractors can make these adjustments, and should make them in consultation with their sealer producer. But before tinkering with recommended mix designs it is imperative to understand some fundamentals that relate to film formation and the factors which influence the proper set and final cure of sealer films.

Let's start with the basics - sealer composition, film formation, and the conditions for proper film formation - before finally discussing the adjustment of mix designs.

Some sealcoating basics
Most sealcoatings are intimate dispersions of refined coal tar or asphalt cement, clay, emulsifiers and specialty chemicals in water. Being water-based, sealcoatings are safe to handle and store. Over the decades it has been established that sealcoatings provide years of protection to asphalt surfaces when applied properly and allowed to cure under the right ambient conditions.

The major components of a sealer are:

• Refined coal tar or asphalt is the binder or the glue that holds the inorganic fillers (clay, sand/aggregate, etc.) tightly bound in the sealer film after full cure. Both asphalt and coal tar are thermoplastic materials, meaning that they soften and melt at higher temperatures (about 100°F to 180°F, higher for asphalt) and become hard at cooler temperatures (below 60°F).
• Binder is the backbone of sealcoating. It is the component that protects the asphalt in the pavement. In the wet (uncured) state, sealer contains a fine dispersion of binder particles in the range of 2 to 5 microns (human hair is approximately 25 microns), either in spherical or elongated cigar shapes. Upon full cure the binder forms a continuous film, enveloping the filler particles (1 to 2 microns) thus holding them tightly in the cured film.
• Clay, fillers, and aggregates impart toughness and dimensional stability to sealcoating film and counteract the tackiness of binder at elevated surface temperatures.
• Specialty chemicals, such as surfactants and emulsifiers, keep the binder and filler particles properly suspended and dispersed in the wet state, providing a stable system.
• Water is the fluid medium in which the above components are dispersed.

Mix designs